Energy, t/s, is counter-spacial and forms shells of harmonics and phase relationships to create what we observe from our 3D spacial reference frame to be a series of concentric spheres in space. Due to inversion of observation at the unit boundary, even though outward in counter-space is towards the point at infinity, the reciprocal nature of space and time provides for the "opposite"... the whole structure must be observed as inside-out. i.e. the inner-most shell in 3D time becomes our outer-most shell in 3D space.The electrons in the outermost shell (the ones with the highest value of n) are the most energetic, and are the ones which are exposed to other atoms. This shell is known as the valence shell. The inner, core electrons (inner shell) do not usually play a role in chemical bonding.
Bonding is not caused by sharing or exchanging electrons, valence or otherwise. Bonding occurs when atoms geometrically arrange in space (or not) as to create a zero net-speed for the overall arrangement.Elements with similar properties generally have similar outer shell configurations. For instance, we already know that the alkali metals (Group I) always form ions with a +1 charge; the "extra" s1 electron is the one that's lost.
Love the quotes about 'prefer.' More electronically stable = closer to zero net speed? i.e. less "reactive"?The next shell down is now the outermost shell, which is now full — meaning there is very little tendency to gain or lose more electrons. The ion's electron configuration is the same as the nearest noble gas — the ion is said to be isoelectronic with the nearest noble gas. Atoms "prefer" to have a filled outermost shell because this is more electronically stable.
Source: https://www.angelo.edu/faculty/kboudrea ... umbers.htm
Reference: Martin S. Silberberg, Chemistry: The Molecular Nature of Matter and Change, 2nd ed. Boston: McGraw-Hill, 2000, p. 277-284, 293-307.