Electrovalency

Electrovalency

Electrovalency is manifested by the transfer of electrons, and gives rise to the ionic bond. Consider sodium chloride. Sodium is (1s)²(2s)²(2p)⁶(3s): chlorine is (1s)²(2s)²(2p)⁶(3s)²(3p)⁵. Sodium has completed K and L shells, and is starting the M shell with one electron. This electron (the 3s electron) is the valency electron of sodium. Chlorine has completed K and L shells, and has seven electrons in the M shell. These M electrons are the valency electrons of chlorine. If the sodium completely transfers its valency electron to the chlorine atom, t hen each atom will have eight electrons in its outermost shell, and this, as we have seen, is a stable arrangement. Since both atoms were originally electrically neutral, the sodium atom, in losing one electron, will now have a single positive charge, i.e., the neutral atom has become a positive ion. Similarly, the neutral chlorine atom, in gaining one electron, has become a negative ion. In the sodium chloride crystal these ions are held together by electrostatic forces. If the symbol of an element is used to represent the nucleus of an atom and all the electrons other than the valency electrons and dots are used to represent the valency electrons, then the combination of the sodium and chlorine atoms to form sodium chloride may be represented as follows: