# My text seems to say that the high(est) energy orbitals are not valence orbitals - everything else says otherwise. What's true?

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

The outermost orbital shell of an atom is called its valence shell, and the electrons in the valence shell are valence electrons. Valence electrons are the highest energy electrons in an atom and are therefore the most reactive.

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?

• 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. – M.A.R. May 31 '15 at 21:01
• @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? – – Hal May 31 '15 at 21:12
• Well, the shell involved in bonding is the most energetic shell that is occupied by electrons. – M.A.R. May 31 '15 at 21:13
• 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. – M.A.R. May 31 '15 at 21:18

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.
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.