Gribbin (1988: 116-7):
The simplest [electron] clouds are spherical and centred on the nucleus. The two electrons in the helium atom occupy these simplest orbitals, the lowest energy state. At the next level up the energy ladder, however, things are a little more complicated. The wave equation does indeed predict the existence of another spherically symmetrical state, into which two more electrons with slightly more energy than the two innermost electrons can slot. But alongside it, at very nearly the same energy, there are three more standing wave patterns, shaped rather like short, fat dumb-bells, or hour glasses, at right angles to each other. Two electrons are able to slot into each of these orbitals, giving a total number of eight (2 + 6) for the filled outer shell. Things get still more complicated at higher energy levels. But the quantum mechanical wave equation exactly predicts how many electrons can fit into each shell, and this explains the structure of the periodic table of elements. The quantum maths also tells us that although some electrons do fit spherically around their nuclei, very many electron orbitals have a definite shape and a definite orientation with respect to one another. In very many cases, electron orbitals stick out from atoms in certain clearly defined, and predictable, directions.
Blogger Comments:
From the perspective of Systemic Functional Linguistic theory, differences in the shape and extent of electron clouds are construals of (experience as) differences in the potential locations of quanta.
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