A paragraph in my text reads

Bonding involves the valence orbitals almost exclusively because these orbitals have the appropriate energies to interact strongly. Examine the electron energy-level diagram of a fluorine atom. The core $1 \mathrm{s}$ orbitals on a fluorine atom are at much lower energies than any of the $n = 2$ orbitals and do not participate effectively in bonding with other atoms. On the other hand, orbitals with $n > 2$ lie at considerably higher energy than the $n = 2$ orbitals. These orbitals can interact, but the resulting orbitals are too unstable to form strong covalent bonds. Therefore, the only orbitals of fluorine that form chemical bonds are the valence orbitals, those with $n = 2$. Typically the highest energy occupied orbitals are the ones used to bond with other atoms.

In contrast this simple paragraph from SparkNotes expresses what I had believed to be the case


I had thought that the outermost shell, the valence shell, the most energetic shell, and the shell involved in molecular bonds were all the same thing. However, the quoted paragraph of my text says otherwise. Where have I gone wrong?

  • $\begingroup$ Ooof, I have a little problem understanding your problem. None of the things you quoted cancel each other. Note that for a Neon atom, for instance, there is an n=4; it's just that it's vacant and "not occupied" by electrons in the base state. $\endgroup$
    – M.A.R.
    May 31 '15 at 21:01
  • $\begingroup$ @M.A.Ramezani What about 'orbitals with n>2 lie at considerably higher energy than the n=2 orbitals... but the resulting orbitals are too unstable to form covalent bonds.' Does that not preclude the largest and most energetic shell from being the shell involved in bonding? – $\endgroup$
    – Hal
    May 31 '15 at 21:12
  • 3
    $\begingroup$ Well, the shell involved in bonding is the most energetic shell that is occupied by electrons. $\endgroup$
    – M.A.R.
    May 31 '15 at 21:13
  • $\begingroup$ Hal anytime! I'm pretty sure others will come and write better and more explained answers, and I'm going to sleep now, so I'm not changing that into an answer. $\endgroup$
    – M.A.R.
    May 31 '15 at 21:18

The problem is the words used to describe energy. I am not native english speaker so I am not the best person to answer your question but I'll try.

As smaller $n$, smaller energy. Problems arises when the words higher lower are used to compare numeric values (as those of the energy). They must say greater or smaller.

Without accurate words all of us intuitively agree in that: "2 is higher that 1", and we should say that 2 is greater than 1 (2>1)

When negative numbers are involved it is not so clear. For some authors "-2 is higher than -1" and "-2 is higher than 1", for others "-2 is lower than -1" and "-2 is lower than 1". In the later cases the correct word is "smaller" (-2<-1).

In this context energies are negatives because of the definition of the reference states. So the energy of an $1s$ orbital is smaller than the energy of a $2s$ orbital.

I have some discrepancies about the meaning and usage of orbital energies but I adopted the common usage to avoid extra confusions.


Your Answer

