Valence Electrons

By definition, valence electrons are those electrons in an atom which have the largest value for the quantum number n. Thus ₂₀Ca, with a configuration of 1s²2s²2p⁶3s²3p⁶4s², has two valence electrons (the two 4s electrons), and ₃₅Br, with a configuration of 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁵, has seven valence electrons (the two 4s and the five 4p electrons).

For representative elements (s and p block elements), the number of valence electrons is always the (Roman numeral) group number. For example, sulfur is in group VI and has six valence electrons.

Capacity of shell subshell are given by such expressions 2n² and 2(2l+1)

1 If the nucleus were the size of a tennis ball, its electron would most likely be found at a distance of 2 miles from the nucleus.

2 The 1905 volume of Annalen der Physik is now an expensive collector’s item, for in that year Einstein published three major papers, any one of which would have guaranteed him his place in posterity. The first, on the photoelectric effect, eventually won him the Nobel Prize. The second paper, on Brownian motion, amounted to the first direct confirmation of the atomic theory of matter. The third paper, his most famous, “On the electrodynamics of moving bodies”, set forth the special theory of relativity.

i Example of wave properties: interference