Pure elements, 145 semi-metals

Semi-metal impure (amorphous) boron is a brown powder the pure element is shiny, silver grey. 

Another type of mixed bond is foimd for some elements in Groups IIIA, IVA, and VA of the periodic table (viz., B, Si, Ge, As, Sb, Te, Po, and At). Interatomic bonds for these elements are mixtures of metallic and covalent, as noted on Figure 2.25a. These materials are called the metalloids or semi-metals, and their properties are intermediate between the metals and nonmetals. In addition, for Group IV elements, there is a gradual transition from covalent to metallic bonding as one moves vertically down this column—for example, bonding in carbon (diamond) is purely covalent, whereas for tin and lead, bonding is predominantly metallic. 

Fig. 2-19. Dependence of concentration C and mass m of accumulated metal in an element collector on time x 1- pure diffusion accumulation (j=0 E(U=0) 2- migration under the action of an external electric field (j 0) 3- diffusion accumulation with action of a double electrical layer of semi-permeable membrane ( 15 0) (reproduced with permission from Putikov, 1993).

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