a. Except for hydrogen (and Helium) how many electrons are contained in the valence shell of an atom after it has bonded? 2, 4, 6, 8, 10

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Example:

Sodium Chloride - chlorine has 7 electrons in its valance shell, electronic confrugation being (2,8,7) and sodium has 1 electron in its valance shell EC for sodium is (2,8,1) Hence 1 electron from sodium is transferred to valance shell of chlorine full filling its octet and as sodium losses a electron, its 2nd shell has fullfilled octet rule.

Eight electrons i. e. octet must be complete in valance shell of a atom after its bonding.