An example of an alternative conception:
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.
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
Read about The octet framework
A related alternative conception suggests there are large jumps in successive ionisation energies when an octet is disrupted because of a special stability of octets of electrons. However, some learners think that an atom or ion with a full outer shell cannot be ionised / further ionised (or that an atom or ion with an outer shell octet cannot be ionised /further ionised).
Read about a diagnostic probe for classroom use to check learners' ideas about ionnisation energy.
[Please be aware that a word may have different nuances, or even a different meaning, according to context.]« Back to Index
