Tag: elements

Can phosphorus prevent rusting?

Is phosphorus the alumina of the ancient world?

Keith S. Taber

An ancient iron column: Did "a very thin layer of phosphorus formed, between the rust and the fresh metal and basically stop… it from rusting any more"

What do you need to build a skyscraper?

I was listening to a podcast from the Royal Institution (where Humphrey Davy and Michael Faraday were based). I must confess I had downloaded the 'Recipe for a Skyscraper' episode some time ago but it had been passed over for other titles.

Royal Institution podcast: Recipe for a Skyscraper – with Roma Agrawal

My mistake. In this talk "structural engineer Roma Agrawal delves into the history of the materials that enable immense construction and the developments that have made our structures what they are today. All while noting the accomplishments of key visionary engineers of the past". This proved to be an engaging and fascinating talk.

A 'mega badass engineer'

On her website, Roma Agrawal , "a structural engineer, author and broadcaster, with a physics degree" describes herself as a "mega badass engineer". She is not above being a little mischievous.

The crumbly ages

For example, she has her own take on what historians used to call the 'dark ages', 1

"So, oddly enough, once the Roman empire fell, the use of concrete basically ended for nearly a thousand years, so that we call it the dark ages, or the crumbly ages as I like to call it, because they went back to using slightly older [construction materials], you know, mud and brick and things like that."

Roma Agrawal talking at the Royal Institution

But while the Romans may have championed the use of concrete, the Indians were outperforming them in the production of high quality iron: "The Romans actually used to import Indian steel at the time and they never knew how to make it because that secret was closely guarded…"

Iron is too reactive to be found 'native' but has to be produced by roasting its ores (that contain compounds of iron) with materials that will reduce the iron compounds to iron, and produce, as a by-product, slag – a complex mixtures of substances. The iron produced will contain some slag mixed into the metal unless this is carefully removed. 2

The Delhi column

As an example of the Indian expertise, Roma Agrawal referred to an old iron column near Delhi which "had not rusted" despite having been erected 1500 years ago.3 The column had originally been a stand for a statue of Garuda, the divine winged creature/demigod who acted as the vehicle for Vishnu. Garuda seems to have flown, but the iron column remains.

The (not quite 4) 'rustless wonder' (Srinivasan & Ranganathan, 2013): the Qtub Iron Pillar

(Photograph taken by Mark A. Wilson, available at https://en.wikipedia.org/wiki/Iron_pillar_of_Delhi#/media/File:QtubIronPillar.JPG)

Lord Vishnu on his mount Garuda (wood carving). It is thought the iron pillar near Delhi once supported a statue of Garuda.

(Image by waradet from Pixabay)

Iron is the main constituent of alloys known as steels, and by mixing other elements (principally, but not only, carbon) with iron it is possible to create steels with various properties, including corrosion resistance. 2 But iron itself readily rusts. The rust formed when iron corrodes is permeable and crumbly, exposing the unreacted metal beneath, which in turn forms rust that again fails to protect the iron beneath it. So, over time, a piece of iron can simply 'rust away' as the reacted material will simply fall off, or be eroded by weather.

Yet this iron column, erected around the time of the final collapse of the Roman Empire, seems to have survived throughout 'the crumbly ages' and through to the present day. Although, it is not that it never started rusting 4, but rather,

"it did initially rust, but then because of the climate in Delhi, the phosphorus, a very thin layer of phosphorus formed, between the rust and the fresh metal and basically stopped it from rusting any more…"

Roma Agrawal talking at the Royal Institution

Corrosion (as with tarnishing) is a generic term. Corrosion leads to structural damage to metal objects (whereas tarnishing is a surface effect).

Rusting is specific to iron as it refers to the material produced when iron corrodes – i.e., rust.

Unreactive phosphorus?: An alternative conception

Roma Agrawal's claim seems incredible to a chemist or science teacher because phsophorus is a very reactive element, and a very reactive element does not seem a good choice of material to protect iron from reacting! Even if the phosphorus did not itself react with the iron and so corrode it, it would soon react with air. In the laboratory, some forms of phosphorus can burst into flames spontaneously, suggesting it is very unlikely to remain intact very long exposed to the elements in India. Certainly not many centuries.

Sacrificial elements

Now, sometimes a more valuable metal is protected by connecting it physically to a more reactive but less valuable metal which preferentially corrodes. As the metals are in electrical contact, the one that loses electrons and releases cations more readily reacts first. The metal allowed to corrode is called a 'sacrificial' metal. For example, bars of sacrificial metal may be dangled from piers or oil rigs to protect the structural metal. The sacrificial metal will slowly 'dissolve' away into the sea 5 – but not that slowly that it would not need replacing for over a millennium. In any case, phosphorus is a non-metal, where the sacrificial element of the pair needs to be the more electropositive. So, there is no helpful explanation there.

Alumina – when tarnishing prevents corrosion

Aluminium is a more reactive metal than iron, yet does not readily undergo substantive corrosion. This is because the surface of an aluminium object readily reacts with oxygen from the air to form a layer of aluminium oxide (alumina). This then protects the aluminium because the alumina formed is a fairly inert substance (unlike the highly reactive phosphorus), and it forms an impermeable layer (preventing oxygen from the air reaching the metal beneath).

Any layer that were to form on iron protect it from rusting also needs to be impermeable and relatively inert. Unlike reactive phosphorus.

Phosphorus would not protect iron

Phosphorus is a fire hazard that burns to produce toxic fumes. In the laboratory, the direct reaction of iron and phosphorus usually requires heating to initiate reaction. Without active heating, the rate of reaction would be too low for a useful laboratory process. However, a very low rate of reaction would not prevent reaction over the centuries since the iron column was erected.

Even if phosphorus was able to form a layer that coated over the iron, using it as a means to prevent corrosion would be like fireproofing a wooden building by coating it with petroleum jelly (e.g., Vaseline). [A correspondent to the British Dental Journal (Brewer, 2017) warned of "the death of a bedbound patient who smoked following application of E45 cream…a paraffin-based product, the residue of which can act as an accelerant when ignited". Smoking kills. And even more rapidly if you smother yourself in flammable oil products prior to lighting up.]

So, it seems we have a mystery.

Or, Roma Agrawal simply got it wrong.

Or, perhaps, more likely, when Roma Agrawal refers to a 'layer of phosphorus' she is using the term loosely, and is actually referring to something else. That is, the protective layer may contain one or more phosphorus compounds, but not phosphorus – just as a layer of the unreactive aluminium compound alumina stops corrosion, although aluminium itself is reactive. Is this distinction just being pedantic? Not to a science educator.

An elementary misconception

The claim that a layer of phosphorus could protect iron from corrosion is therefore not credible to the scientifically literate, but might seem perfectly reasonable to a person with limited science background. One of the great challenges of learning chemistry is making sense of the set of ideas that:

  • the compound of an element is a completely different substance to the element itself
  • the properties of compounds are often quite different (sometimes contrastingly so) to those of the elements the compound was formed from
  • although the compound does not behave like the elements, and does not 'contain' the elements in any straightforward way, there is a sense in which something of the elements persists in (and so the element may be recovered from) the compound.

So, sodium is a reactive metal that burns in air, and chlorine is a green, toxic, choking gas; and both should be avoided unless taking very careful precautions; yet they react, very energetically, to give the relatively unreactive compound sodium chloride – which people readily use in cooking, and to season their food, and to dissolve in water to gargle with, or to soak tired feet. Chlorine would destroy the lining of your throat. Yet sodium chloride solution (despite its chlorine 'constituent') will help ease a sore throat! Still, the sodium chloride has the potential to be 'separated' into the elements with their dangerous properties intact.

Although the distinction between elements and compounds is a lot easier to understand once students learn about molecules and atoms (at least, if avoiding the alternative conception that compounds comprise of molecules and elements comprise of atoms!) this topic is fraught with complications and hang-overs from historical ideas about atoms (Taber, 2003).

If not a layer of phosphorus?

The chemist or science teacher hearing about a protective 'layer of phosphorus' preventing rusting will immediately thinks this is not viable…but a compound of phosphorus might well have the necessary properties. Indeed, generally, the more reactive the elements, the more stable the compounds they form when reacting.

It seems that the layer that formed on the iron column contains the phosphorus compound iron hydrogen phosphate hydrate (FePO4·H3PO4·4H2O),

"Several theories have been postulated regarding corrosion resistance of the Delhi iron pillar. Some of those refer to the inherent nature of the construction material, such as the selection of pure iron, presence of slag particles and slag coatings, surface finishing using mechanical operation, phosphate film formation, or the Delhi's climate…

Earlier studies have delineated the formation of crystalline iron hydrogen phosphate hydrate (FePO4·H3PO4·4H2O), 𝛼-, 𝛾-, 𝛿-FeOOH and magnetite in the case of Delhi iron pillar"

Dwivedi, Mata, Salvemini, Rowles, Becker & Lepková, 2021
The claim re-interpreted

Yet this critical, and somewhat counter-intuitive, distinction between elements qua elements and elements as in some sense 'components' (or 'ingredients') of compounds needs to be acquired. Novices have to learn this. A common alternative conception is to assume that the properties of elements are carried over into their compounds.

So, if students hear that

  • phosphorus is essential in our diet, and that
  • phosphorus is important for healthy bones and teeth,

they can draw the obvious and reasonable conclusion – that phosphorus must be a pretty innocuous substance as it is part of our bodies and we eat it quite safely in our food. Actually, we need compounds of phosphorus in our food to allow our metabolisms to build and repair tissues that contain phosphorus compounds – and anyone misguided enough to try to eat any actual (elemental) phosphorus risks a nasty burn.

In conclusion, as a science graduate, Roma Agrawal presumably appreciates the key distinction between (i) elements as substances and (ii) elements as chemically combined components of other substances, and, as a structural engineer knowledgeable about different material properties, is using 'layer of phosphorus' as a shorthand for a layer of material that includes one or more phosphorus compounds.

That is fine as long as those hearing her talk appreciate that. Another scientist would likely automatically hear 'phosphorus layer' as meaning 'phosphorus compound containing layer'. A science teacher, however, might suspect that the reference to how "a very thin layer of phosphorus formed, between the rust and the fresh metal and basically stopped it from rusting" is likely to be misunderstood, and indeed to mislead, some listening to the podcast.

Minding your Ps…

One of the sources referred to reported how:

"P is found present in slag whereas the presence of P in iron was not detected within the limit of the analytical techniques used in this study. On the basis of this result, we speculate application of lime and other basic compounds during the iron making process which would have led to the transfer P to slag."

Dwivedi, Mata, Salvemini, Rowles, Becker & Lepková, 2021

P is the symbol for phosphorus, the element. However, someone with a sufficient scientific background appreciates from the context that references to

  • P found in slag
  • P in iron
  • transfer [of] P to slag

cannot refer to P as phosphorus the element, but rather some compound or compounds of phosphorus. As a reactive element, phosphorus is not found native and so would not be present (as an element) in the raw materials and, in any case, could certainly not survive (as an element) the high temperature conditions of the processes of iron smelting. Therefore the relevant 'context' for reinterpreting 'P' as not standing for the element itself would be any set of circumstances other than the special conditions where phosphorus can be safely stored without risk of reaction.

This is the prerequisite background knowledge that prevents an audience member misinterpreting what must be meant by a "thin layer of phosphorus [sic]" protecting an exposed iron column – as it cannot possibly refer to a thin layer of [actual, elemental] phosphorus.

Sources cited
  • Anantharaman, T. R. (1997). The iron pillar at Delhi. In S. Ranganathan (Ed.), Iron and Steel Heritage of India (pp. 1-28). Indian Institute of Metals and Tata Steel.
  • Brewer, E. Patient safety: Paraffin-based products. British Dental Journal 223, 620 (2017). https://doi.org/10.1038/sj.bdj.2017.936
  • Dwivedi, D., Mata, J. P., Salvemini, F., Rowles, M. R., Becker, T., & Lepková, K. (2021). Uncovering the superior corrosion resistance of iron made via ancient Indian iron-making practice. Scientific Reports, 11(1), 4221. doi:10.1038/s41598-021-81918-w
  • Falk, S. (2020). The Light Ages. A Medieval journey of discovery. Allen Lane.
  • Srinivasan, S., & Ranganathan, S. (2013). Minerals and Metals Heritage of India. Bangalore: National Institute of Advanced Studies.
  • Taber, K. S. (2003). The atom in the chemistry curriculum: fundamental concept, teaching model or epistemological obstacle? Foundations of Chemistry, 5(1), 43-84. (The author's manuscript versions is available here.)

Notes:

1 A simplistic view was that advancing civilisation underwent something of a relapse during the middle ages, until the gains of the classical age (the Greeks, the Romans) were rediscovered in the Enlightenment. Thus, the term 'dark ages' applied to the 'middle ages'.

There were no dark ages:
as a matter of fact, they are all dark

with apologies to Pink Floyd

That is clearly a great simplification, and ignores many medieval achievements, as well as being a rather Eurocentric view. Some historians have been seeking to redress this impression: for example, Seb Falk (2020) has renamed this period 'the light ages'.

2 To suggest that steel deliberately contains impurities added to iron could give the impression that iron artefacts are made of purer materials than steel ones. This is misleading. Basic iron smelting produces iron that is impure (sometimes known as 'pig iron') and which can contain quite high levels of impurities. Pig iron typically has a high level of carbon – more than is usually used in steels.

Wrought iron is produced by physical working of pig iron which expels much of the slag content, giving purer iron. Wrought iron has long been widely used in structures, but still does not have a high level of purity.

Alloys are mixtures of different metals, or of metallic elements with other elements. 'Metal' here is ambiguous as it can refer to

  • an electropositive element (the usual meaning in chemistry) or
  • a material with certain properties (the usual meaning in engineering) – i.e., malleable, ductile, high electrical and thermal conductivities, lustre, sonorous.

Steels are metals in the 'materials' sense, but 'chemically' are mixtures of the metallic element iron with other elements.

As the properties of steels are sensitive to the levels of other elements, making steel requires using high quality iron that has been treated to remove most of the impurities. This is similar to doping a semiconductor such as silicon to produce electronic components. Very pure silicon is needed as a starting point, so that just the right amount of a specific dopant can be added.

The Indian iron manufacture of Roman times tended to produce iron with a significant phosphorus content.

3 The column was made of wrought iron,

"The forging of wrought iron seems to have reached its zenith in India in the first millennium AD. The earliest large forging is the famous iron pillar with a height of over 7 m and weight of about 6 tons at New Delhi ascribed to Chandragupta Vikramaditya 400- 450 CE… the absence of corrosion is linked to the composition, the high purity of the wrought iron and the phosphorus content and the distribution of slag."

Srinivasan & Ranganathan, 2013

4 The lack of rusting may have been exaggerated,

"The first impression in 1961 was that the portion of the Pillar below the earth was "superficially rusted". However, on detailed examination, the buried portion of the Pillar was found covered with thick crusts of rust and, in fact, copious rust scales could be collected, ranging in thickness from a few millimeters (mm) to no less than 15 mm in some portions. Further, the bulbous base of the Pillar was found riddled with numerous cavities and hollows caused by deep corrosion and mineralization of the iron.

Anantharaman, 1997

Even so, the survival of an iron column exposed to weathering for this length of time is still worthy of note.

5 I thought I should put 'dissolve' into 'scare quotes' here. Corrosion is a chemical change, whereas dissolving refers to what is generally considered a physical change. As the sacrificial metal reacts, it releases cations into solution in the sea, in much the same was as, say, dissolving salt releases sodium ions when common salt is added to water. The metal reacts and enters solution – dissolves, if you are comfortable with that word in this context.

Using water to feed the fire

How NOT to heat up your blast furnace

Keith S. Taber

"From one of the known ingredients of steam being a highly inflammable body, and the other that essential part of the air which supports combustion, it was imagined that [steam] would have the effect of increasing the fire …"

Producing iron requires high temperatures: adding H2O does not help
(Image by zephylwer0 from Pixabay)

The challenge of chemical combination

School science teachers are likely aware of how chemistry poses some significant leaning challenges for learners. One of these is the nature of chemical compounds. That is, compounds of chemical elements.

It may seem obvious to learners that when we 'mix' two components with different properties we should get a mixture with a combination of the component properties. So far, so good. But of course, in chemical reactions we do not just mix different substances, but rather they chemically react. So, sodium will react with chlorine, which can be understood in terms of processes occurring at the nanoscopic scale where molecules of a gas interact with the metallic lattice of sodium cations and delocalised electrons.

Sodium and chlorine behaving badly

Although we can model this process, we cannot observe it directly, or even the starting structures at that scale. Understandably, students often struggle to relate the macroscopic and molecular:

As Sodium is a reactive meterial [sic] and chlorine is a acid. When Sodium is placed in Chlorine, Sodium react badly making a flame and maybe a noise. I think why this reaction happen is because as Sodium reactive metal meaning that it atomic configuration is unstable make the metal danger And as Chlorine is a dangerous acid. When sodium is placed in Chlorine, the sodium start dissolving in the acid due to all the particle rushing around quickly pushing together with Chlorine atom. Producing Sodium chloride.

Student setting out on Advanced level chemistry, quoted in Taber, 1996

So, for example, if we do burn sodium in chlorine we end up with sodium chloride which is a new substance that has its own properties – properties which are not simply some mixture of, or intermediate between, the properties of the substances we start with (the reactants).

Indeed, sodium is a dangerous material to handle: it will react vigorously with water (in a person's sweat for example!) and burns violently in air. Chlorine is so nasty that it has been used as a weapon of war (and since banned as an 'unacceptable' weapon, even in war). In the 'great' war ('great' only because of its scale) the way men died in agony from breathing chlorine was much reported, as well as the effects on those who survived the gas – being blinded for example.

"In all my dreams before my helpless sight,

He plunges at me, guttering, choking, drowning."

Wilfred Owen, Dulce et Decorum Est 1
Sweet and honourable? 1 (Image by Bruce Mewett from Pixabay)

Sodium chloride certainly has its associated hazards – if eaten in excess it is a risk factor for high blood pressure for example – but is certainly not dangerous in anything like the same sense. Many people put sodium chloride on their chips (often along with ethanoic acid solution). No one would want sodium on their food, or to eat in a canteen with a chlorine atmosphere!

When is something both present and not present?

Why this is especially challenging is that the chemistry teacher tells the students that although, at one level, the new substance does not contain its precursors – there is no sodium (substance) or chlorine (substance) in the substance sodium chloride – yet it is a compound of these elements and in some some sense the elements remain 'in' the compound.

Learning chemistry requires understanding how disciplinary concepts explained in terms of submicroscopic level models (After Figure 5, Taber, 2013)

This links to that key theoretical framework in chemistry where we can explain macroscopic (bench scale) phenomena in terms of models of matter at the submicroscopic (indeed nanoscopic or even subnanoscopic) scale. The sense in which sodium chloride 'contains' sodium and chlorine is that it is comprised of a lattice of sodium ions and chloride ions – species which include the specific types of nuclei (those of charge +11 and +17 respectively) that define those elements.

So, when we ask whether the elements are in some sense 'in' the compound we have to think in terms of these abstract models at a tiny scale – there is no sodium substance or chlorine substance present, but there is something that is inherently identified with these two elements. In a sense, but a very abstract sense, the elements are still present. Or, perhaps, better, something intrinsic to those elements is still present.

"We are working here with two complementary meanings for the idea of element, one at the (macroscopic) level of phenomena we can demonstrate to students (substances, and their reactions); the other deriving from a theoretical model in terms of conjectured submicroscopic entities ('quanticles'…).

However, there is also a sense in which an element is considered to be present, in a virtual or potential sense, within its compounds. This use is more common among French-speaking chemists, and in the English-speaking world we normally consider it quite inappropriate to suggest that sodium is somehow present in sodium chloride, or hydrogen in water. Yet, of course, chemical formulae (NaCl, H2O, etc) tell us that the compounds somehow 'contain' the elements."

Taber, 2012, p.19
Figure 1.9 from Taber, 2012

A source of alternative conceptions

This is easy to understand for someone very familiar with molecular level models – but is understandably difficult for novice learners. Thus we can reasonably understand why there are common alternative conceptions along the lines of students thinking that, for example, a compound of a dangerous element (say chlorine) must also be dangerous. Yet we 'mix' and react a soft, reactive, metal and a choking green gas – and get hard white crystals that safely dissolve in water to give a solution we can use in cooking, or to soak our feet, or to gargle with.

An historical precedent

Because science teachers and chemists are so used to thinking in models at the molecular level, we can forget just how unfamiliar this perspective is to the novice, and so the challenge of acquiring the scientific ways of thinking that have become 'second nature' through extensive application.

I was therefore fascinated to see an example of this same alternative conception, assuming a compound will show the properties of its constituent elements, reported by the scientist Sir John Herschel (astronomer, chemist, mathematician, philosopher…), not in a school science context, but rather an industrial context.

"The smelting of iron requires the application of the most violent heat that can be raised, and is commonly performed in tall furnaces, urged by great iron bellows driven by steam-engines. Instead of employing this power to force air into the furnace through the intervention of bellows, it was, on one occasion, attempted to employ the steam itself in, apparently, a much less circuitous manner; viz. by directing the current of steam in a violent blast, from the boiler at once into the fire. From one of the known ingredients of steam being a highly inflammable body, and the other that essential part of the air which supports combustion, it was imagined that this would have the effect of increasing the fire to tenfold fury, whereas it simply blew it out; a result which a slight consideration of the laws of chemical combination, and the state in which the ingredient elements exist in steam, would have enabled any one to predict without a trial."

Herschel, J. F. W. (1830/1851/2017), §37 2

So, here, instead of dropping marks on a test, this misunderstanding of the chemistry leads to a well-intentioned industrialist trying to generate heat in a blast furnace by adding water to the fire. But this does remind us just how counter-intuitive some of the things taught in science are. It might also be a useful anecdote to share with students to help them appreciate that that their errors are by no means unusual, or necessarily a reflection on their ability.

Perhaps this might even be a useful teaching example that could be built up into a historical anecdote which students might readily recall and that will help them remember that compounds have new properties that may be quite different from their constituent elements. So, while a mixture of the flammable gas hydrogen and oxygen can be explosive, a combination (that is, a chemical combination – a compound), of hydrogen and oxygen will not 'feed' a fire but dampen it down. Just as well, really, as otherwise emergency fire and rescue services would need to find an alternative to the widely available, inexpensive, recyclable, non-toxic, agent they widely use in fighting fires.

Compounds and mixtures are not interchangeable (Image by David Mark from Pixabay)
Work cited:
Notes:

1 Wilfred Owen was famous for his war poetry written about the horrors of the trench fighting in the 'first world war'. Owen was killed a week before the war ended. 'Dulce Et Decorum Est' referred to a Latin phrase or motto (dulce et decorum est pro patria mori) that Owen labelled as 'the old lie', that it was sweet and honourable to die in the service of one's country.

2 For some reason, "…it was imagined that this would have the effect of increasing the fire to tenfold fury, whereas it simply blew it out…" puts me in mind of

"the mighty ships tore across the empty wastes of space and finally dived screaming on to…Earth – where due to a terrible miscalculation of scale the entire battle fleet was accidentally swallowed by a small dog."

Douglas Adams, The Hitchhiker's Guide to the Galaxy

Acute abstracts correcting Copernicus

Setting the history of science right

Keith S. Taber

I recently read a book of essays by Edward Rosen (1995) who (as described by his publisher) was "the editor and translator of Copernicus' complete works, was the leading authority on this most celebrated of Renaissance scientists". Copernicus is indeed, rightly, highly celebrated (for reasons I summarise below *).

The book was edited by Rosen's collaborator, Erna Hilfstein 1, and although the book was an anthology of reprinted journal articles, none of the chapters (articles) had abstracts. This reflects different disciplinary norms. In the natural and social sciences most journals require abstracts – and some even offer a menu of what should be included – but abstracts are not always expected in humanities disciplines.

Read about the abstract in academic articles

A collection of published papers from various journals – all lacking abstracts

It is not unusual for an academic book to be a compilation of published articles – especially when anthologising a single scholar's work. I was a little surprised to find the different chapters in the same book having different formats and typefaces – it had been decided to reproduce the articles as they had originally appeared in a range of journals (perhaps for authenticity – or perhaps to avoid the costs of new typesetting?)

But it was the absence of article abstracts that most felt odd. The potential reader is given a title, but otherwise little idea of the scope of an article before reading. Perhaps it was my awareness of this 'omission' that led me to thinking that for a number of the chapters it would be possible to offer a very minimal abstract (an acute abstract?) that would do the job! Certainly, for some of these chapters, I thought a sentence each might do.

That is not to dismiss the scholarship that has gone into developing the arguments, but Rosen often wrote on a very specific historical point, set out pertinent ideas from previous scholarship, and then argued for a clear position contrary to some earlier scholars.

So, here are my suggestions for 'acute' abstracts

Six summary encapsulations

Chapter 6: on the priest question

Abstract:

Copernicus has often been described as a priest, but Copernicus was never ordained a priest.

Copernicus was a canon in the Roman Catholic church, but this made him an administrator (and he also acted as physician), but he never became a monk or a priest.

Chapter 7: on the notary question

Abstract:

Copernicus has been described as a 'happy notary' but Copernicus was not a notary.

Although Copernicus had various roles as an administrator, even as something of a diplomat, he never took on the role of a legal notary.

Chapter 8: on the disdain question

Abstract:

Copernicus is sometimes said to have had a dismissive attitude to the common people, but there is no evidence that this was so

A comment of Copernicus on not being concerned with the views of certain philosophers seems to have been misinterpreted.

Chapter 11: on the axioms question

Abstract:

It has been claimed that Copernicus misused the term axioms in his work, but his use was perfectly in line with authorities

Today axioms are usually expected to be the self-evident starting points for developing a deductive argument, but Aristotle's definition of axioms did not require them to seem self-evident.

Chapter 16: on the papal question

Abstract:

It has been claimed that Copernicus' 'Revolutions' was approved by the pope before publication, but the manuscript was never shown to the pope

This seems to be a confusion regarding an anecdote concerning a completely different scholar.

Chapter 17: on the Calvin question

Abstract:

It has been suggested that Calvin was highly critical of Copernicus, but it seems unlikely Calvin had ever heard of him

While Calvin's writing strongly suggest he was committed to a stationary earth and a sun that moved around the earth, there is no evidence he had specifically come across Copernicus.

A manifold chapter

Having noticed how so many of Rosen's articles took one claim or historically contentious idea and developed it in the light of various sources to come to a position, I was a little surprised when I reached Chapter 20, 'Galileo's misstatements about Copernicus', to find that Rosen was dealing with 5 distinct (if related) points at once – several of which he had elsewhere made the unitary focus of an article.

Rather than write my own abstract, I could here suggest a couplet of sentences from the text might have done the job,

"According to Galileo, (1) Copernicus was a priest; (2) he was called to Rome; (3) he wrote the Revolutions by order of the pope; (4) his book was never adversely criticised; (5) it was the basis of the Gregorian calendar. Actually, Copernicus was not a priest; he was not called to Rome; he did not write the Revolutions by order of the pope; the book received much adverse criticism, particularly on the ground that it contradicted the Bible; it was not the basis of the Gregorian calendar."

Rosen, 1958/1995, pp.203-204

I noticed that this was the earliest of Rosen's writings that had been included in the compilation – perhaps he had decided to dispense his ideas more sparingly after this paper?

Actually, there's a lot to be said for abstracts that pithily précise the key point of an article, a kind of tag-line perhaps, acting for a reader as an aide-mémoire (useful at least for readers like me who commonly stare at rows of books thinking 'I read something interesting about this, somewhere here…'). I have also read a lot of abstracts in research journals that would benefit from their own (further) abstracts, so perhaps such acute abstraction might catch on?

* Appendix: A scientific giant

Copernicus is indeed 'celebrated', being seen as one of the scientific greats who helped establish modern ways of thinking about the world – part of what is often perceived as a chain that goes Copernicus – Kelper – Galileo – Newton.

Copernicus is most famous for his book known in English as 'On the Revolutions of the Heavenly Spheres', or just 'Revolutions'. The key point of note is that at a time when it was almost universally agreed that the earth was stationary at the centre of 'the world', i.e., the cosmos, and that everything else revolved around the earth, Copernicus proposed a system that put the sun at the centre and had the earth moving around the sun.

The geocentric model of the cosmos was widely accepted for many centuries
(Image by OpenClipart-Vectors from Pixabay)

From our modern worldview, it is difficult to imagine just how, well yes, revolutionary, that move was (even if Copernicus only moved the centre of the universe from earth to the sun, so our solar system still had a very special status in his system). This is clear from how long it took the new view to become the accepted position, and the opposition it attracted. Newton later realised that strictly the centre of revolution was the centre of mass of the solar system not the sun per se. 2

One problem was that there was no absolute observational test to distinguish between the two models and there were well-established reasons to accept the conventional geocentric model (e.g., we do not feel the earth move, or a great wind as it spins beneath its atmosphere; as the most dense element earth would naturally fall to the centre of the world, beneath water, air, fire, and the ether that filled the heavens {although the Earth was not considered a pure form of the element earth, it was earthy, considered mostly earth in composition 3}; and scriptures, if given a literal interpretation, seemed to suggest the earth was fixed and the sun moved.)

Copernicus' model certainly had some advantages. If the earth is still, the distant sphere with all the fixed stars must be moving about it at an incredible rate of rotation. But if the earth spun on its axis, this stellar motion was just an illusion. 4 Moreover, if everything revolves around the earth, some of the planets behave very oddly, first moving one way, then slowing down to reverse direction ('retrograde' motion), before again heading off in their original sense. But, if the planets are orbiting the sun along with the earth (now itself seen as a planet) but at different rates then this motion can be explained as an optical illusion – "these phenomena…happen on account of the single motion of the earth" – the planets only seem to loop because of the motion of the earth.

Despite this clear improvement, Copernicus model did not entirely simplify the system as Copernicus retained the consensus view that the planets moved in circles: the planets' "motions are circular or compounded of several circles,…since only the circle can bring back the past". With such an assumption the observational data can only be made to fit (either to the heliocentric model or its geocentric alternative) by having a complex series of circles rather than one circle per planet. Today when we call the night sky 'the heavens', we are using the term without implying any supernatural association – but the space beyond the moon was once literally considered as heaven. In heaven everything is perfect, and the perfect shape is a circle.

It was only when Kepler later struggled to match the best observational data available (from his employer Tycho Brahe's observatory) to the Copernican model that, after a number of false starts, he decided to see if ellipses would fit – and he discovered how the system could be described in terms of planets each following a single elliptical path that almost repeated indefinitely.

A well-known story is how by the time Copernicus had finished his work and decided to get it printed he was near the end of his life, and he was supposedly only shown a printed copy brought from the printer as he lay on his deathbed (in 1543). In the printed copy of the book an anonymous foreword/preface 5 had been inserted to the effect that readers should consider the model proposed as a useful calculating system for following the paths of heavenly bodies, and not as a proposal for how the world actually was.

Despite this, the book was later added to the Roman Catholic Church's index of banned works awaiting correction. This only occurred much later – in 1616, after Galileo taught that Copernicus' system did describe the actual 'world system'. But, in the text itself Copernicus is clear that he is suggesting a model for how the world is – "to the best of my ability I have discussed the earth's revolution around the sun" – not just a scheme for calculating purposes. Indeed, he goes as far to suggest that where he uses language implying the sun moves this is only to be taken as adopting the everyday way of talking reflecting appearances (we say 'the sun rises'). For Copernicus, it was the earth, not the sun, that moved.

Sources cited:
  • Copernicus, N. (1543/1978). On the Revolutions of the Heavenly Spheres (E. Rosen, Trans.). Prometheus Books.
  • Rosen, E. (1995). Copernicus and his successors (E. Hilfstein, Ed.). The Hambledon Press.

Notes

1 I discovered from some 'internet research' (i.e., Googling) that Erna was a holocaust survivor, "[husband] Max and Erna, along with their families, were sent first to Płaszów, a slave-labor camp, and then on a death march to Auschwitz".

An article in the Jewish Standard reports how Erna's daughter undertook a charity bike ride "from Auschwitz-Birkenau, the Nazi-run death camp in the verdant Polish countryside, to the" Jewish Community Centre of Krakow (the town where her parents lived before being deported by the Nazis).

2 Newton also wrote as if the solar system was the centre of the cosmos, but of course the solar system is itself moving around the galaxy, which is moving away from most other galaxies…

3 These are not the chemical elements recognised today, of course, but were considered the elements for many centuries. Even today, people sometimes refer to the air and water as 'the elements.'

4 Traditionally, the 'heavenly spheres' were not the bodies such as planets, moons and stars but a set of eight conjectured concentric crystalline spheres that supposedly rotated around the earth carrying the distant stars, Saturn, Jupiter, Mars, the Sun, the Moon, Venus and Mercury.

5 A preface is written by the author of a book. A foreword is written by someone else for the author (perhaps saying how wonderful the author and the work are). Technically then this was a foreword, BUT because it was not signed, it would appear to be a preface – something written by Copernicus himself. Perhaps the foreword did actually protect the book from being banned as, until Galileo made it a matter of very public debate, it is likely only other astronomers had actually scrutinised the long and very technical text in any detail!

Move over Mendeleev, here comes the new Mendel

Seeking the islets of Filipenka Henadzi

Keith S. Taber

"new chemical elements with atomic numbers 72-75 and 108-111 are supposedly revealed, and also it is shown that for heavy elements starting with hafnium, the nuclei of atoms contain a larger number of protons than is generally accepted"

Henadzi, 2019, p.2

Somehow I managed to miss a 2019 paper bringing into doubt the periodic table that is widely used in chemistry. It was suggested that many of the heavier elements actually have higher atomic numbers (proton numbers) than had long been assumed, with the consequence that when these elements are correctly re-positioned it reveals two runs of elements that should be in the periodic table, but which till now have not been identified by chemists.

According to Henadzi we need to update the periodic table and look for eight missing elements (original image by Image by Gerd Altmann from Pixabay)

Henadzi (2019) suggests that "I would like to name groups of elements with the numbers 72-75 and 108-111 [that is, those not yet identified that should have these numbers], the islets of Filipenka Henadzi."

The orginal Mendeleev

This is a bit like being taken back to when Dmitri Mendeleev first proposed his periodic table and had the courage to organise elements according to patterns in their properties, even though this left gaps that Mendeleev predicted would be occupied by elements yet to be discovered. The success of (at least some) of his predictions is surely the main reason why he is considered the 'father' of the periodic table, even though others were experimenting with similar schemes.

Now it has been suggested that we still have a lot of work to do to get the periodic table right, and that the version that chemists have used (with some minor variations) for many decades is simply wrong. This major claim (which would surely be considered worthy of the Nobel prize if found correct) was not published in Nature or Science or one of the prestigious chemistry journals published by learned societies such as the Royal Society of Chemistry, but in an obscure journal that I suspect many chemists have never heard of.

The original Mendel

This is reminiscent of the story of Mendel's famous experiments with inheritance in pea plants. Mendel's experiments are now seen as seminal in establishing core ideas of genetics. But Mendel's research was ignored for many years.

He presented his results at meetings of the Natural History Society of Brno in 1865 and then published them in a local German language journal – and his ideas were ignored. Only after other scientists rediscovered 'his' principles in 1900, long after his death, was his work also rediscovered.

Moreover, the discussion of this major challenge to accepted chemistry (and physics if I have understood the paper) is buried in an appendix of a paper which is mostly about the crystal structures of metals. It seems the appendix includes a translation of work previously published in Russian, explaining why, oddly, a section part way through the appendix begins "This article sets out the views on the classification of all known chemical elements, those fundamental components of which the Earth and the entire Universe consists".

Calling out 'predatory' journals

I have been reading some papers in a journal that I believed, on the basis of its misleading title and website details, was an example of a poor-quality 'predatory journal'. That is, a journal which encourages submissions simply to be able to charge a publication fee (currently $1519, according to the website), without doing the proper job of editorial scrutiny. I wanted to test this initial evaluation by looking at the quality of some of the work published.

One of the papers I decided to read, partly because the topic looked of particular interest, was 'Nature of Chemical Elements' (Henadzi, 2019). Most of the paper is concerned with the crystal structures of metals, and presenting a new model to explain why metals have the structure they do. This is related to the number of electrons per atom that can be considered to be in the conduction band – something that was illustrated with a simple diagram that unfortunately, to my reading at least, was not sufficiently elaborated.1

The two options referred to seem to refer to n-type (movement of electrons) and p-type (movement of electrons that can be conceptualised as movement of a {relatively} positive hole, as in semi-conductor materials) – Figure 1 from Henadzi, 2019: p2

However, what really got my attention was the proposal for revising the periodic table and seeking eight new elements that chemists have so far missed.

Beyond Chadwick

Henadzi tells readers that

"The innovation of this work is that in the table of elements constructed according to the Mendeleyev's law and Van-den- Broek's rule [in effect that atomic number in the periodic table = proton number], new chemical elements with atomic numbers 72-75 and 108-111 are supposedly revealed, and also it is shown that for heavy elements starting with hafnium, the nuclei of atoms contain a larger number of protons than is generally accepted. Perhaps the mathematical apparatus of quantum mechanics missed some solutions because the atomic nucleus in calculations is taken as a point."

Henadzi, 2019, p.4

Henadzi explains

"When considering the results of measuring the charges of nuclei or atomic numbers by James Chadwick, I noticed that the charge of the core of platinum is rather equal not to 78, but to 82, which corresponds to the developed table. For almost 30 years I have raised the question of the repetition of measurements of the charges of atomic nuclei, since uranium is probably more charged than accepted, and it is used at nuclear power plants."

Henadzi, 2019, p.4

Now Chadwick is most famous for discovering the neutron – back in 1932. So he was working a long time ago, when atomic theory was still quite underdeveloped and with apparatus that would seem pretty primitive compared with the kinds of set up used today to investigate the fundamental structure of matter. That is, it is hardly surprising if his work which was seminal nearly a century ago had limitations. Henadzi however seems to feel that Chadwick's experiments accurately reveal atomic numbers more effectively than had been realised.

Sadly, Henadzi does not cite any specific papers by Chadwick in his reference list, so it is not easy to look up the original research he is discussing. But if Henadzi is suggesting that data produced almost a century ago can be interpreted as giving some elements different atomic numbers to those accepted today, the obvious question is what other work, since, establishes the accepted values, and why should it not be trusted. Henadzi does not discuss this.

Explaining a long-standing mystery

Henadzi points out that whereas for the lighter elements the mass number is about twice the atomic number (that is, the number of neutrons in a nucleus approximately matches the number of protons) as one proceeds through the period table this changes such the ratio of protons:neutrons shifts to give an increasing excess of neutrons. Henadzi also implies that this is a long standing mystery, now perhaps solved.

"Each subsequent chemical element is different from the previous in that in its core the number of protons increases by one, and the number of neutrons increases, in general, several. In the literature this strange ratio of the number of neutrons to the number of protons for any the kernel is not explained. The article proposes a model nucleus, explaining this phenomenon."

Henadzi, 2019, p.5

Now what surprised me here was not the pattern itself (something taught in school science) but the claim that the reason was not known. My, perhaps simplistic, understanding is that protons repel each other because of their similar positive electrical charges, although the strong nuclear force binds nucleons (i.e., protons and neutrons collectively) into nuclei and can overcome this.

Certainly what is taught in schools is that as the number of protons increases more neutrons are needed to be mixed in to ensure overall stability. Now I am aware that this is very much an over-simplification, what we might term a curriculum model or teaching model perhaps, but what Henadzi is basically suggesting seems to be this very point, supplemented by the idea that as the protons repel each other they are usually found at the outside of the nucleus alongside an equal number of neutrons – with any additional neutrons within.

The reason for not only putting protons on the outer shell of a large nucleus in Henadzi's model seems to relate to the stability of alpha particles (that is, clumps of two protons and two neutrons, as in the relatively stable helium nucleus). Or, at least, that was my reading of what is being suggested,

"For the construction of the [novel] atomic nucleus model, we note that with alpha-radioactivity of the helium nucleus is approximately equal to the energy.

Therefore, on the outer layer of the core shell, we place all the protons with such the same number of neutrons. At the same time, on one energy Only bosons can be in the outer shell of the alpha- particle nucleus and are. Inside the Kernel We will arrange the remaining neutrons, whose task will be weakening of electrostatic fields of repulsion of protons."

Henadzi, 2019, p.5

The lack of proper sentence structure does not help clarify the model being mooted.

Masking true atomic number

Henadzi's hypothesis seems to be that when protons are on the surface of the nucleus, the true charge, and so atomic number, of an element can be measured. But sometimes with heavier elements some of the protons leave the surface for some reason and move inside the nucleus where their charge is somehow shielded and missed when nuclear charge is measured. This is linked to the approximation of assuming that the charge on an object measured from the outside can be treated as a point charge.

This is what Henadzi suggests:

"Our nuclear charge is located on the surface, since the number of protons and the number of neutrons in the nucleus are such that protons and neutrons should be in the outer layer of the nucleus, and only neutrons inside, that is, a shell forms on the surface of the nucleus. In addition, protons must be repelled, and also attracted by an electronic fur coat. The question is whether the kernel can be considered a point in the calculations and up to what times? And the question is whether and when the proton will be inside the nucleus….if a proton gets into the nucleus for some reason, then the corresponding electron will be on the very 'low' orbit. Quantum mechanics still does not notice such electrons. Or in other words, in elements 72-75 and 108-111, some protons begin to be placed inside the nucleus and the charge of the nucleus is screened, in calculations it cannot be taken as a point."

Henadzi, 2019, p.5

So, I think Henadzi is suggesting that if a proton gets inside the nucleus, its associated electron is pulled into a very close orbit such that what is measured as nuclear charge is the real charge on the nucleus (the number of protons) partially cancelled by low lying electrons orbiting so close to the nucleus that they are within what we might call 'the observed nucleus'.

This has some similarity to the usual idea of shielding that leads to the notion of core charge. For example, a potassium atom can be modelled simplistically for some purposes as a single electron around a core charge of plus one (+19-2-8-8) as, at least as a first approximation, we can treat all the charges within the outermost N (4th) electron shell (the 19 protons and 18 electrons) as if a single composite charge at the centre of the atom. 2

Dubious physics

Whilst I suspect that the poor quality of the English and the limited detail included in this appendix may well mean I am missing part of the argument here, I am not convinced. Besides the credibility issue (how can so many scientists have missed this for so long?) which should never be seen as totally excluding unorthodox ideas (the same thing could have been asked about most revolutionary scientific breakthroughs) my understanding is that there are already some quite sophisticated models of nuclear structure which have evolved alongside programmes of emprical research and which are therefore better supported than Henadzi's somewhat speculative model.

I must confess to not understanding the relevance of the point charge issue as this assumption/simplification would seem to work with Henadzi's model – from well outside the sphere defined by the nucleus plus low lying electrons the observed charge would be the net charge as if located at a central point, so the apparent nuclear charge would indeed be less than the true nuclear charge.

But my main objection would be the way electrostatic forces are discussed and, in particular, two features of the language:

Naked protons

protons must be repelled, and also attracted by an electronic fur coat…

I was not sure what was meant by "protons must be repelled, and also attracted by an electronic fur coat". The repulsion between protons in the nucleus is balanced by the strong nuclear force – so what is this electronic 'fur coat'?

This did remind me of common alternative conceptions that school students (who have not yet learned about nuclear forces) may have, along the lines that a nucleus is held together because the repulsion between protons is balanced by their attraction to the ('orbiting') electrons. Two obvious problems with this notion are that

  • the electrons would be attracting protons out of the nucleus just as they are repelling each other (that is, these effects reinforce, not cancel), and
  • the protons are much closer to each other than to the electrons, and the magnitude of force between charges diminishes with distance.

Newton's third law and Coulomb's law would need to be dis-applied for an electronic effect to balance the protons' mutual repulsions. (On Henadzi's model the conjectured low lying electrons are presumably orbiting much closer to the nucleus than the 1s electrons in the K shell – but, even so, the proton-electron distance will be be much greater than the separation of protons in the nucleus.)3

But I may have misunderstood what Henadzi's meant here by the attraction of the fur coat and its role in the model.

A new correspondence principle?

if a proton gets into the nucleus for some reason, then the corresponding electron will be on the very 'low' orbit

Much more difficult to explain away is the suggestion that "if a proton gets into the nucleus for some reason, then the corresponding electron will be on the very 'low' orbit". Why? This is not explained, so it seems assumed readers will simply understand and agree.

In particular, I do not know what is meant by 'the corresponding electron'. This seems to imply that each proton in the nucleus has a corresponding electron. But electrons are just electrons, and as far as a proton is concerned, one electron is just like any other. All of the electrons attract, and are attracted by, all of the protons.

Confusing a teaching scheme for a mechanism?

This may not always be obvious to school level students, especially when atomic structure is taught through some kind of 'Aufbau' scheme where we add one more proton and one more electron for each consecutive element's atomic structure. That is, the hydrogen atom comprises of a proton and its 'corresponding' electron, and in moving on to helium we add another proton, with its 'corresponding' electron and some neutrons. These correspond only in the sense that to keep the atom neutral we have to add one negative charge for each positive charge. They 'correspond' in a mental accounting scheme – but not in any physical sense.

That is a conceptual scheme meant to do pedagogic work in 'building up' knowledge – but atoms themselves are just systems of fundamental particles following natural laws and are not built up by the sequential addition of components selected from some atomic construction kit. We can be misled into mistaking a pedagogic model designed to help students understand atomic structure for a representation of an actual physical process. (The nuclei of heavy elements are created in the high-energy chaos inside a star – within the plasma where it is too hot for them to capture the electrons needed to form neutral atoms.)

A similar category error (confusing a teaching scheme for a mechanism) often occurs when teachers and textbook authors draw schemes of atoms combining to form molecules (e.g., a methane molecule formed from a carbon atom and four hydrogen atoms) – it is a conceptual system to work with the psychological needs for students to have knowledge built up in manageable learning quanta – but such schemes do not reflect viable chemical processes.4

It is this kind of thinking that leads to students assuming that during homolytic bond fission each atom gets its 'own' electron back. It is not so much that this is not necessarily so, as that the notion of one of the electrons in a bond belonging to one of the atoms is a fiction.

The conservation of force conception (an alternative conception)

When asked about ionisation of atoms it is common for students to suggest that when an electron is removed from an atom (or ion) the remaining electrons are attracted more strongly because the force for the removed electron gets redistributed. It is as if within an atom each proton is taking care of attracting one electron. In this way of thinking a nucleus of a certain charge gives rise to a certain amount of force which is shared among the electrons. Removing an electron means a greater share of the force for those remaining. This all seems intuitive enough to many learners despite being at odds with basic physical principles (Taber, 1998).

I am not deducing that Henadzi, apparently a retired research scientist, shares these basic misconceptions found among students. Perhaps that is the case, but I would not be so arrogant as to diagnose this just from the quoted text. But that is my best understanding of the argument in the paper. If that is not what is meant, then I think the text needs to be clearer.

The revolution will not be televised…

In conclusion, this paper, published in what is supposedly a research journal, is unsatisfactory because (a) it makes some very major claims that if correct are extremely significant for chemistry and perhaps also physics, but (b) the claims are tucked away in an appendix, are not fully explained and justified, and do not properly cite work referred to; and the text is sprinkled with typographic errors, and seems to reflect alternative conceptions of basic science.

I very much suspect that Henadzi's revolutionary ideas are just wrong and should rightly be ignored by the scientific community, despite being published in what claims to be a peer-reviewed (self-describing 'leading international') research journal.

However, perhaps Henadzi's ideas may have merit – the peer reviewers and editor of the journal presumably thought so – in which case they are likely to be ignored anyway because the claims are tucked away in an appendix, are not fully explained and justified, and do not properly cite work referred to; and the text is sprinkled with typographic errors, and seems to reflect alternative conceptions of basic science. In this case scientific progress will be delayed (as it was when Mendel's work was missed) because of the poor presentation of revolutionary ideas.

How does the editor of a peer-reviewed journal move to a decision to publish in 4 days?
Let down by poor journal standards

So, either way, I do not criticise Henadzi for having and sharing these ideas – healthy science encompasses all sorts of wild ideas (some of which turn out not to have been so wild as first assumed) which are critiqued, tested, and judged by the community. However, Henadzi has not been well supported by the peer review process at the journal. Even if peer reviewers did not spot some of the conceptual issues that occurred to me, they should surely have noticed the incompleteness of the argument or at the very least the failures of syntax. But perhaps in order to turn the reviews around so quickly they did not read the paper carefully. And perhaps that is how the editor, Professor Nour Shafik Emam El-Gendy of the Egyptian Petroleum Research Institute, was able to move to a decision to publish four days after submission.5

If there is something interesting behind this paper, it will likely be missed because of the poor presentation and the failure of peer review to support the author in sorting the problems that obscure the case for the proposal. And if the hypothesis is as flawed as it seems, then peer review should have prevented it being published until a more convincing case could be made. Either way, this is another example of a journal rushing to publish something without proper scrutiny and concern for scientific standards.

Works cited
Footnotes:

1 My understanding of the conduction band in a metal is that due to the extensive overlap of atomic orbitals, a great many molecular orbitals are formed, mostly being quite extensive in scope ('delocalised'), and occurring with a spread of energy levels that falls within an energy band. Although strictly the molecular orbitals are at a range of different levels, the gaps between these levels are so small that at normal temperatures the 'thermal energy' available is enough for electrons to readily move between the orbitals (whereas in discrete molecules, with a modest number of molecular orbitals available, transitions usually require absorption of higher energy {visible or more often} ultraviolet radiation). So, this spread of a vast number of closely spaced energy levels is in effect a continuous band.

Given that understanding I could not make sense of these schematic diagrams. They SEEM to show the number of conduction electrons in the 'conduction band' as being located on, and moving around, a single atom. But I may be completely misreading this – as they are meant to be (cross sections through?) a tube.

"we consider a strongly simplified one- dimensional case of the conduction band. Option one: a thin closed tube, completely filled with electrons except one. The diameter of the electron is approximately equal to the diameter of the tube. With such a filling of the zone, with the local movement of the electron, there is an opposite movement of the "place" of the non-filled tube, the electron, that is, the motion of a non-negative charge. Option two: in the tube of one electron – it is possible to move only one charge – a negatively charged electron"

Henadzi, 2019, p.2

2 The shell model is a simplistic model, and for many purposes we need to use more sophisticated accounts. For example, the electrons are not strictly in concentric shells, and electronic orbitals 'interpenetrate' – so an electron considered to be in the third shell of an atom will 'sometimes' be further from the nucleus than an electron considered to be in the fourth shell. That is, a potassium 4s electron cannot be assumed to be completely/always outside of a sphere in which all the other atomic electrons (and the nucleus) are contained, so the the core cannot be considered as a point charge of +1 at the nucleus, even if this works as an approximation for some purposes. The effective nuclear charge from the perspective of the 4s electron will strictly be more than +1 as the number of shielding electrons is somewhat less than 18.

3 Whilst the model of electrons moving around the nucleus in planetary orbits may have had some heuristic value in the development of atomic theory, and may still be a useful teaching model at times (Taber, 2013), it seems it is unlikely to have the sophistication to support any further substantive developments to chemical theory.

4 It is very common for learners to think of chemistry in terms of atoms – e.g., to think of atoms as starting points for reactions; to assume that ions must derive from atoms. This way of thinking has been called the atomic ontology.

5 I find it hard to believe that any suitably qualified and conscientious referees would not raise very serious issues about this manuscript precluding publication in the form it appears in the journal. If the journal really does use peer review, as is claimed, one has to wonder who they think suitable to act as expert reviewers, and how they persuade them to write their reports so quickly.

Based on this, and other papers appearing in the journal, I suspect one of the following:

a) peer review does not actually happen, or

b) peer review is assigned to volunteers who are not experts in the field, and so are not qualified to be 'peers' in the sense intended when we talk of academic peer review, or

c) suitable reviewers are appointed, but instructed to do a very quick but light review ignoring most conceptual, logical, technical and presentation issues as long as the submission is vaguely on topic, or

di) appropriate peer reviewers are sought, but the editor does not expect authors to address reviewer concerns before approving publication, or possibly

dii) decisions to publish sub-standard work are made by administrators without reference to the peer reviews and the editor's input

Elements as chemical seasoning?

Keith S. Taber

An analogy for the importance of trace elements

Unseen minerals all around us (Ockham's Razor – ABC)

I was listening to a recent episode of 'Ockhams' razor' (ABC's series of short science and technology essays) from 2020 called 'Unseen minerals all around us'. As a radio programme, the audience was likely to be diverse in terms of age, interests, and background knowledge and experiences.

The speaker was Allison Britt, Director of Mineral Resources Advice and Promotion, Geoscience Australia ("Australia's pre-eminent public sector geoscience organisation"), and she was describing the large number of elements used in constructing a modern mobile phone – apparently someone had put a phone in a laboratory blender and analysed the smoothie produced! (Please note: that is not a safe activity for a home science practical.)

Allison Britt, Director of Mineral Resources Advice & Promotion, Geoscience Australia – at a live recording of 'Okham's razor'. (Source: Twitter)

As a science teacher (well, retired – but once a science teacher, always a science teacher at heart at least) I tend to be primed to focus on the ways in which teachers and scientists 'make the unfamiliar familiar', and Britt used an analogy with multiple targets.

(Read about 'making the unfamiliar, familiar')

(Read about science analogies)

The source domain was something familiar from everyday life – seasoning food.

I thought this worked really well, although as a purist (and, as noted here before, something of a pedant) I would have liked the third of her comparisons to refer to a difference that was a matter of degree (e.g., 'taste better' cf. 'work more efficiently'). That said, Britt's formulation worked better as scientific poetry:

So, just like adding salt and pepper to a meal makes it taste better:

putting a little rhenium in a jet engine makes it burn faster and hotter;

putting a little scandium in an aeroplane makes it lighter and stronger;

and putting a little indium in your mobile phone makes the touchscreen work.

Britt, 2021

This was an example of a science communicator making the point of how adding a small, sometimes trace, quantity of a substance can make a substantive difference to properties. I imagine that virtually everyone listening to this would have effortlessly understood the comparison – a key criterion for an effective teaching analogy.

She'd never thought about whether ionic bonding is the same thing as chemical bonding

Keith S. Taber

Amy was a participant in the Understanding Science Project. When I talked to her near the start of her GCSE 'triple science' course in Y10 she told me that ionic bonding was "atoms which have either lost or gained electrons so they are either positively or negatively charged" and that chemical bonding was "like in a compound, where two or more elements are joined together", but she seemed unsure how the two concepts were related.

I followed up on Amy's use of the term 'compound' to explore how she understood the term:

How would you define a compound?

Erm …Something which has erm two or more elements chemically bonded.

… So you give me an example of that, compound?

Erm, sodium oxide.

Sodium oxide, okay, so there are two or more elements chemically bonded in sodium oxide are there?

Uh hm

And what would those two or more elements be?

Sodium and oxygen.

Okay. Erm, so when we say sodium oxide is chemically bonded, what we are saying there is?

[pause, c 2s]

Erm – a sodium atom has been bonded with a oxygen atom to form erm a new substance.

So Amy's example of a compound was sodium oxide, which would normally be considered essentially an ionic compound, that is a compound with ionic bonding. So this gave me an opportunity to test out whether Amy saw the bonding in sodium chloride and sodium oxide as similar.


Okay, so that was chemical bonding,

Mm.

and that occurs with compounds?

Yeah.

And what did you say about ionic bonding?

Erm, it's the outer electrons they are transferred from one element to another.

Now what does that occur in? You gave me one example, didn't you?

Uh huh

Sodium chloride?

Yeah
…

Erm. Would sodium chloride be er an element?

[pause, c.2s]

Sodium chloride, no.

No?

It would be a compound.

You think that would be a compound?

Yeah.

And a compound is two or more elements joined together by chemical bonding?

Yeah.

So Amy had told me that sodium chloride, which had ionic bonding, was (like sodium oxide) a compound, and she had already told me that a compound comprised of "two or more elements chemically bonded", so it should be follow that sodium chloride (which had ionic bonding) had chemical bonding.

Do you think sodium chloride has chemical bonding?

Er – I think so

And it also has ionic bonding, or is that the same thing?

Erm,

[pause, c.2s]

I dunno, I've never thought about it that way, erm,

[pause c.3s]

I'm not sure, erm

[pause, c.2s]

I dunno, it might be.

Clearly, whatever Amy had been taught (and interviewing students reveals they often only recall partial and distorted versions of what was presented in class) she had learnt

  • (1) that ionic bonding was transfer of electrons (an alternative conception) as in the example of sodium transferring an electron to chlorine; and that
  • (2) a compounds was where two or more elements chemically bonded together, and an example was sodium oxide where the elements sodium and oxygen were chemical bonded.

Yet these two pieces of learning seemed to have been acquired as isolated ideas without any attempt to link them. Initially Amy seemed to feel ionic bonding and chemical bonding were quite separate concepts.

When taken through an argument that led to her telling me that sodium chloride, that she thought had ionic bonding, was a compound, which therefore had chemical bonding, there should have been a logical imperative to see that ionic bonding was chemical bonding (actually, a kind of chemical bonding – as the logic did not imply that chemical bonding was necessarily ionic bonding). Despite the implied syllogism:

  • sodium chloride has ionic bonding
  • sodium chloride is a compound
  • compounds have elements chemically bonded together
  • therefore ionic bonding …

Amy was unsure what to deduce, presumably because she had seen the two concepts of ionic bonding and chemical bonding as discrete notions and had had given no thought to a possible relationship between them. However explicit teaching had been on this point, it is very likely that the teacher had expected students to appreciate that ionic bonding was a type of chemical bonding – but Amy had not integrated these ideas into a connected conceptual structure (i.e., there was a learning bug that could be called a fragmentation learning impediment).

Ionic bonding – where the electron's transferred to complete the outer shell

Keith S. Taber

Amy was a participant in the Understanding Science Project. The first time I talked to Amy, near the start of her GCSE 'triple science' course in Y10 she told me that "in normal chemistry (i.e., the chemistry part of 'double science', as opposed to the optional additional chemistry lesson as part of 'triple science' that Amy also attended) we're doing about ionic bonding" which was "atoms which have either lost or gained electrons so they are either positively or negatively charged" and

"how the outer electron's transferred…to complete the outer shell of the erm chlorine, thing, ion…and the sodium atom loses erm, one electron is it, yeah one electron, erm, which the chlorine atom gains, and that yeah that completes its outer shell and makes the sodium positively charged and the chlorine negatively charged".

Amy told me that "in ionic bonding it's the electrons that are transferred, I think."

So Amy had acquired a common alternative conception, i.e. that ionic bonding involved electron transfer, and that this occurs to atoms to complete their electron shells.

Ionic bonding refers to the forces between ions that hold the structure of an ionic substance together, rather than a mechanism by which such ions might hypothetically be formed – yet often learners come away form learning about ionic bonding identifying it with a process of electron transfer between atoms instead of interactions between ions which can be used to explain the properties of ionic substances.

Moreover, the hypothetical electron transfer is a fiction. In the case of NaCl such an electron transfer between isolated Na and Cl atoms would be energetically unfavourable, even if reactants containing discrete atoms were available (which is unrealistic).

Whether students are taught that ionic bonding is electron transfer is a moot point, but often introductory teaching of the topic focuses not on the nature of the bonding, but on presenting a (flawed) teaching model of how the ions in the ionic structure could form by electron transfer between atoms. As this mechanism is non-viable, and so not an authentic scientific account, it may seem odd that teachers commonly offer it.

One explanation may simply be custom or tradition has made this an insidious alternative conception. Science teachers and textbooks have 'always' offered the image of electron transfer as representing ionic bonding. So, this is what new teachers had themselves been taught at school, is what they often see in textbooks, and so what they learn to teach.

Another possible explanation is in terms of what what is known as the atomic ontology. This is the idea that the starting pint for thinking about chemistry at the submicroscopic level is atoms. Atoms do not need to be explained (as if in nature matter always starts as atoms – which is not the case) and other entities such as ions and molecules do need to be explained in terms of atoms. So, the atomic ontology is a kind of misleading alternative conceptual framework for thinking about chemistry at the submicroscopic level.

Atoms within an element don't need to be bonded …

Atoms within an element don't need to be bonded because they're all the same sort

Keith S. Taber

Annie was a participant in the Understanding Chemical Bonding project. She was interviewed near the start of her college 'A level' course (equivalent to Y12 of the English school system). Annie was shown, and asked about, a sequence of images representing atoms, molecules and other sub-microscopic structures of the kinds commonly used in chemistry teaching. Annie was shown a representation of the close packing of 'atoms' in a metal (with the iron symbol, Fe, shown).

Okay, have a look at number 6…

• • • • • • (pause, c.6 s)

They are obviously iron atoms within an element.

Iron atoms within the element?

Yeah.

Okay. Can you say anything about the arrangement of the atoms?

They're all lined together. They're all close together.

They're closely together, yes, and they're all lined together, there's some sort of regular pattern there okay?

Yeah.

So you think that's in the element, that's a lump of iron, a sort of, a magnified view of a lump of iron.

Yes.

So Annie did recognise the image as representing particles ('atoms') in solid iron. The image showed the particles close together, and Annie was asked if they would hold together – the intention being to find out what, if anything, Annie knew about metallic bonding. Annie did think the atoms would be held together, but she did not suggest this was due to a bond or even a force (cf. "Sodium and chlorine don't actually overlap or anything and would probably get held together by just forces"*).

Do you think those atoms will hold together?

Yes.

Why do you think that is?

Because they're all the same sort.

Does that make them hold together?

Yeah.

So it seemed that Annie held an alternative conception that atoms of the same sort would hold together because they were of the same type. This interpretation was tested.

Yeah? Do you think there is any kind of bonds between the atoms?

• • • • • • • • • (pause, c.9s)

No, because they're all the same and they don't need to be bonded.

Right, okay so recapping…here we've got an example of something where the atoms are all the same, and that holds them together even though there's no chemical bonds.

Yeah.

So Annie held an alternative conception of atomic coherence – that atoms of the same type did not need bonding to hold them together, as being the same kind of atom was sufficient for them to hold together.

It is unlikely that Annie had been taught this idea, and it seems quite possible it is an intuitive idea that might be acting as an example of a 'grounded learning impediment': a notion based on general experience, and inappropriately applied in the context of atomic interactions.

An element needs a certain number of electrons

An element needs a certain amount of electrons in the outer shell

Keith S. Taber

Bert was a participant in the Understanding Science project. In Y10 Bert was talking about how he had been studying electrolysis in class. Bill had described electrolysis as "where different elements are, are taken out from a compound", but it transpired that Bert thought that "a compound is just a lot of different elements put together"*. He seemed to have a tentative understanding that electrolysis could only be used to separate elements in some compounds.

if they're positive and negative then they would be able to be separated into different ones.

So some things are, some things aren't?

Yeah, it matters how many electrons that they have.

Ah. [pause, c.3s] So have you got any examples of things that you know would definitely be positive and negative?

Well I could tell you what happens.

Yeah, go on then.

Well erm, well if a, if an element gives away, electrons, then it becomes positive. But if it gains, then it becomes negative. Because the electrons are negative, so if they gain more, they just go a bit negative.

Yeah. So why would an element give away or gain some electrons? Why would it do that?

Because erm, it needs a certain amount of electrons in the outer shell. It matters on what part of the periodic table they are.

Okay, let me be really awkward. Why does it need a certain number of electrons in the outer shell?

[Pause, c.2 s]

Erm, well, I don't know. It just – 

So Bert thought that an element "needs a certain amount of electrons in the outer shell" depending upon it's position in the periodic table, but he did not seem to recall having been given any reason why this was. The use of the term 'needs' is an example of anthropomorphism, which is commonly used by students talking about atoms and molecules. Often this derives from language used by teachers to help humanise the science, and provide a way for students to make sense of the abstract ideas. If Bert comes to feel this is a sufficient explanation, then talk of what an element needs can come to stand in place of learning a more scientifically acceptable explanation, and so can act as a grounded learning impediment.

References to atoms needing a certain number of electrons is often used as an explanatory principle (the full shells explanatory principle) considered to explain why bonding occurs, why reactions occur and so forth.

Bert's final comment in the short extract above seems to reflect a sense of 'well that's just the way the world is'. It is inevitable that if we keep asking someone a sequence of 'well, why is that' question when they tell us about their understanding of the world, they eventually reach the limits of their understanding. (This tendency has been labelled 'the explanatory gestalt of essence'.) Ultimately, even science has to accept the possibility that eventually we reach answers and can not longer explain further – that's just the way the world is. Research suggests that some students seem to reach the 'it's just natural' or 'well that's just the way it is' point when teachers might hope they would be looking for further levels of explanation. This may link to when phenomena fit well with the learner's intuitive understanding of the world, or tacit knowledge.

Bert's reference to an element needing a certain amount of electrons in the outer shell also seems to confuse description at two different levels: he explicitly refer to substance (element), when he seems to mean a quanticle (atom). Element refers to the substance, at the macroscopic level of materials that can be handled in the laboratory, whilst an atom of the element (which might better be considered to gain or lose electrons) is part of the theoretical model of matter at a submicroscopic level, used by chemists as a basis for explaining much macroscopic, observed behaviour of samples of substances.


A compound is just a lot of different elements put together

Keith S. Taber

Bert was a participant in the Understanding Science project. When interviewed in Y10 he reported that he had been studying electrolysis in chemistry:

"that's where different elements are, are taken out from a compound…there's a positive anode and a negative cathode. And what it does it attracts the positive part of the compound to the negative cathode, and the negative part goes to the positive , to, you know, so that they can erm get the different elements in the different places, so they can just have one element on its own".

To fully understand what this means from a chemical context the learner needs to appreciate the chemical distinction between elements, compounds and mixtures, so I asked Bert what he thought a compound was:

It's erm, it's er two, er you know, it's just a lot of different elements put together – to create just one.

So if I went and got some elements, let's say I went and got a little file of carbon, a little file of sulphur, a little file of copper, er a little file of magnesium and I were to mix them into a beaker, maybe get a glass rod, give it a good stir, er, give me a compound?

Erm, so it's carbon, erm, carbon, sulphur, magne¬. Carbon, er – What's the fourth one?

Carbon, sulphur, magnesium and copper I think I said.

And copper. All right, erm. Copper, copper sulphate and – and carbon, and I think carbon and magnesium might go just as elements.

Okay, so if I ignored the carbon and magnesium,

Yeah.

if I took some copper and some sulphur,

Yeah.

and mixed them up together,

Yeah.

then I'd get copper sulphate.

Yeah.

And that's a compound now?

Yeah.

In chemistry there is a crucial difference between a mixture and a compound: one which it appeared Bert had not at this point acquired. Presumably his chemistry teacher, in teaching the topic of electrolysis was assuming students in the class would apply prior learning about the difference between elements and compounds, so as to appreciate the significance of electrolysis as a technique which brings about an energetically unfavourable chemical change. This prerequisite knowledge appeared to be lacking for Bert, which provided a deficiency learning impediment when it came to understanding the teaching on electrolysis.

Read about learners' alternative conceptions