Unary Crystalline Substances

In the unary substances case, the atoms, being identical, have equal radii and electronegativity, so their organization in solid state depends only by the distribution of the external electrons the present discussion follows (Chiriac-Putz-Chiriac, 2005). 

Form this point of view, the atoms can be classified in four categories, as follows  

This is the situation of the elements which, in the solid state, form a metallic bonding. This kind of bonding is not oriented in the space, so the ordering of the atoms represent the principle of the maximum compactness for most of the situations. 

The deficit of electrons is obvious for the elements of groups lA-IIIA, of transitions and of the internal transition elements (with 4f and 5f orbitals). For the metals of the p-block (Sn, Pb, Sb, Bi, 

FIGURE 4.26 The metals of the periodic system with the specific types of packing (face) CC-cubic compact (or FCC), HC-hexagonal compact, body centered cubic (BCC), 4H-hexagonal alternate after Heyes (1999). 

---