Solids with two types of atoms

Another way of achieving a stable lattice composed of two kinds of ions with opposite sign, is to place them in the two interpenetrating FCC sublattices of the diamond lattice, described earlier. In this case each ion has four nearest neighbors of the opposite type, as shown in Fig. 1.14. Many combinations of atoms in the I-B column of the Periodic Table and group VII-B atoms crystallize in this structure, which is called the zincblende structure from the German term for ZnS, the representative solid with this lattice. 

The elements in the I-B column have a filled rf-shell (ten electrons) and one extra 5 valence electron, so it is natural to expect them to behave in some ways similar to the alkali metals. However, the small number of neighbors in this structure, as opposed to the rock-salt and cesium chloride structures, suggest that the cohesion of these solids cannot be attributed to simple ionic bonding alone. In fact, this becomes more pronounced when atoms from the second (group II-B) and sixth (group VI-A) 

7 Hydrogen a special ones-valence-electron atom 

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