"Hydrogen has just one electron, close to the nucleus. Helium has two electrons, each at the same distance from the nucleus. Lithium has three electrons, the first two at the same distance from the nucleus as the helium electrons (in the same 'electron shell', in the jargon of quantum theory), with the third slightly further out from the nucleus. … Without the exclusion principle, all atoms would collapse to the size of a hydrogen atom…"
John Gribbin (1996) Companion to the Cosmos. (Ed., Mary Gribbin) Weidenfeld & Nicolson.
This alternative conception (which ignores the different positive charge on different atomic nuclei) is commonly found among learners, and is here repeated in a science reference book.
"Hund's Rule states that in order for electrons to be in a state of lowest energy, no electron pairing takes place until each orbital in the sublevel contains one electron.
If the empty seats on a bus represent the available orbitals in a given sublevel, one would normally observe that strangers would tend to sit in separate seats until all the seats contain one person, then begin pairing up.
A stranger who came and sat on your seat even though other empty seats were available, might put you into an anxious or 'excited' state since you would be wishing the person would move to an unoccupied seat."
Previously posted at scienceanalogies.com by retired science teacher Murray Hart – original source: Goh, Ngoh Khang; Chia, Lian Sai; and Tan, Daniel. Some Analogies for Teaching Atomic Structure at the High School Level Journal of Chemical Education September 1994, 71(9), p.733
A stranger who sits next to you on the bus when there are double seats free behaves like an electron that disobeys one of Hund's rules
Many examples of science analogies are listed in 'Creative comparisons: Making science familiar through language. An illustrative catalogue of figurative comparisons and analogies for science concepts'. Free Download.
An example of an analogy used in a popular science book:
"Thus, in contrast to the outer body of the atom, where the electrons forming various atomic shells have plenty of space in which to move about, the picture of the nucleus is that of a large number of nucleons packed as tightly together as sardines in a can."
George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.
Many examples of science analogies are listed in 'Creative comparisons: Making science familiar through language. An illustrative catalogue of figurative comparisons and analogies for science concepts'. Free Download.
"The first completed shell must consist of 2 electrons, the next two shells of 8 electrons each, and all following shells of 18 each."
George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.
This is a rather odd error for a physicist to make, although this topic confuses many learners as it is only in the first two shells that the shell become full before electrons start fulling the subsequent shell. (So an atom of potassium, configuration 2.8.8.1 , does not have a full third shell). The third shell only becomes full at 18 electrons (not 8), and the fourth shell at 32 electrons (not 18) and the fifth shell at 50 electrons (not 18).
An example of an analogy used to describe an historical model of the atom:
"Thus Rutherford's discovery shrank the originally widespread positive charge of Thomson's atomic model into a tiny atomic nucleus in the very centre of the atom, leaving the swarm of negative electrons on the outside, so that instead of being similar to a watermelon with electrons playing the role of seeds, the picture of the atom began to look more like a miniature solar system with an atomic nucleus for the sun, and electrons for planets…"
George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.
Many examples of science analogies are listed in 'Creative comparisons: Making science familiar through language. An illustrative catalogue of figurative comparisons and analogies for science concepts'. Free Download.
Describing the electrons as being in a swarm is an example of metaphor.
Many examples of science metaphors are listed in 'Creative comparisons: Making science familiar through language. An illustrative catalogue of figurative comparisons and analogies for science concepts'. Free Download.
"As an 𝛂-particle passes through the atoms of the target material, it is influenced by the forces of attraction towards atomic electrons and the forces of repulsion from the positive parts of the atom. Since, however, the electrons are so exceedingly light, they are no more able to influence the motion of the incident 𝛂-particle, than a swarm of mosquitoes can influence the run of a scared elephant. On the other hand the repulsion between the massive positive parts of the atom and the positive charge of incident 𝛂-particles must be able to deflect the latter from their ordinary trajectory and to scatter them in all directions , provided they pass sufficiently close by one another."
George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.
Many examples of science analogies are listed in 'Creative comparisons: Making science familiar through language. An illustrative catalogue of figurative comparisons and analogies for science concepts'. Free Download.
Learners commonly think that, apart from in period 1 (where the electron shell is filled by two electrons), atoms have full outer shells with eight electrons.
This is the case for period 2, but not for period 3 (18 electrons in a full shell) and beyond.
Yet some elementary text books suggests that a full shell in period 3 would be eight electrons. If this were the case, many substances met in more advanced courses (e.g. PCl5, many of the interhaolgrens such as IF7) could not exist.
Indeed, some substances met in introductory courses, such as the sulphates and nitrates (and sulphuric and nitric acids) would not exist.
Learners commonly think there is a special stability associated with noble gas electronic configurations, due to the presence of full shells or outer shell octets of electrons.
Some therefore think that when an atom is ionised, only the outer shell electrons can be removed as this will lead a full outer shell or octet of electrons.
This particular alternative conception fits in a much more expansive conceptual framework explaining chemistry in terms of the 'desirability' / stability of octets or full outer shells
The noble gas elements have higher standard molar first ionisation energies (enthalpies), s.m.f.i.e., than the other elements in the same period. So, for example, neon has the highest s.m.f.i.e., in period 2 and argon has the highest s.m.f.i.e., in period 3.
Learenrs commonly suggest that the noble gas elements' high values of s.m.f.i.e are due to the noble gas atoms having full outer shells of electrons, or due to them having octets of electrons in the valence shell. (This is the same thing for the period 2 element, neon.) It is commonly thought that the nobel gas configurations have a special stability, and a full shell/octet is especially dificult to disrupt.
However, s.m.f.i.e. increaes across a period as the core charge increases, and as atomic radius tends to decrease. If s.m.f..i.e. is plotted against atomic number then it is seen that neon fits a general pattern in period 2 and argon fits a general pattern in period 3 that can be explained in terms of other factors: core charge (or effective nuclear charge), type of orbital from which electron is being removed, and ionic radius.
Figure 5: Factors influencing the pattern of first ionisation energies (SMFIE) across period 3.
This particular alternative conception fits in a much more expansive conceptual framework explaining chemistry in terms of the 'desirability' / stability of octets or full outer shells
