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Physical Properties of Group 14 Elements

Group 14 of the periodic table consists of elements carbon (C), silicon (Si), germanium (Ge), tin (Sn) and lead (Pb).
  1. Elements of Group 14 have outer electronic configuration ns2np2, where n varies from 2 to 6. The elements exhibit +4 covalent oxidation state.
  2. Carbon, being the first element of the group, differs from the rest of elements of the group because of its small size, high electro-negativity and non-availability of d orbitals.
  3. The group starts from a nonmetal and ends with a metal. There is increase in the metallic character on descending the group.

Carbon is a nonmetals and Silicon is a metalloid.
Ge is a nonmetal but also has some metallic characteristics
Sn and Pb are metals.
  1. The covalent and ionic radii increase on descending the group.
    The small difference in sizes between Si and Ge is due the intervening 3d electrons in Ge which shields the nuclear charge less effectively.
    Similarly, the small difference in sizes between Sn and Pb may be explained on the basis of intervening 4f electrons in case of Pb.
  2. The melting points decrease on descending the group, with the exception of Pb whose melting point is slightly higher than that of Sn4).
Carbon has extremely high melting point. This is due to the stronger C—C bonds in the network of carbon atoms which has face-centred cubic lattice (known as diamond lattice).

The melting points of Si and Ge are also high. Both these elements have diamond type crystal lattice. The decrease in melting point from C to Si to Ge is due to the weakening of the M—M bond caused by the increase in covalent radii of the element.

The melting points of Sn and Pb are low. They do not use all four outer electrons for metallic bonding.
  1. The boiling points of the elements of Group 14 also decrease on descending the group.
  2. The ionization energies decrease from C to Si, but then change in an irregular way because of the effects of filling d and f sub-shells (Fig. 10.25).
The sum of the first four ionization energies is exceptionally large, so the formation of M4+ ions is excluded.
The compounds of Sn and Pb with the highly electronegative elements F and O are significantly ionic. The oxidation state of these elements in the compounds is primarily +2.
  1. The phenomenon of catenation (ability of like atoms to link one another through covalent bonds) decreases down the group. This phenomenon is linked with the M—M bond enthalpy, which decreases down the group.
  2. Besides sigma bond, carbon forms pπ—pπ multiple bonding with itself and with other nonmetals; especially nitrogen and oxygen (e.g. C = C, C C, C N, C = O, C = S).            
  3. Maximum covalency of carbon is four, whereas the other elements of group can exhibit maximum valence of six due to the participation is d orbitals
    (e.g. [SiF6]2-, [Sn(OH)6]2-, [GeCl6]2- and [Pb(Cl)6]2-). 

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