The elements Carbon (C), Silicon (Si), Germanium (Ge), Tin (Sn) and Lead (Pb) together constitute the 14th group of the long form of Periodic table and are known as members of the carbon family. Carbon and silicon are non-metals, Ge is a metalloid (with greater metallic properties) while Sn and Pb are typical metals.
General Trends in Physical Properties of Carbon Family:
(i) Electronic Configuration- The general outer electronic configuration of group 14 elements is ns2 np2 (n = 2 to 6) which shows that these elements have four electrons in the valence shell; two in s-orbital and two in p-orbital.
|Element / Symbol||Atomic Number||Electronic Configuration|
|Carbon, C||6||1s2, 2s2 2p2 or [He] 2s2 2p2|
|Silicon, Si||14||1s2, 2s2 2p6, 3s2 3p2 or [Ne] 3s2 3p2|
|Germanium, Ge||32||1s2, 2s2 2p6, 3s2 3p6 3d10, 4s2 4p2 or [Ar] 3d10, 4s2 4p2|
|Tin, Sn||50||1s2, 2s2 2p6, 3s2 3p6 3d10, 4s2 4p6 4d10, 5s2 5p2 or [ Kr] 4d10, 5s2 5p2|
|Lead, Pb||82||1s2, 2s2 2p6, 3s2 3p6 3d10, 4s2 4p6 4d10 4f14, 5s2 5p6 5d10, 6s2 6p2 or [Xe] 4f14, 5d10, 6s2 6p2|
(ii) Density- Except carbon, the densities of elements of group 14 increase with the increase in atomic number. This is due to a greater and steady rise in atomic mass in comparison to the increase in atomic size.
(iii) Atomic radii and Ionic radii- The atomic radii of group 14 elements are smaller than corresponding elements of group 13 due to their greater nuclear charge. However, on moving down the group from C to Pb, atomic radii show an increasing trend due to an increase in screening effect which overcomes the effect of increased nuclear charge. Like atomic radii, ionic radii of group 14 elements also shows an increasing trend on moving down the group.
(iv) Melting points and Boiling points- The melting point and boiling point of carbon is exceedingly high, but there is no regular trend in the variation of melting points and boiling points as we move down the group from C to Pb. The melting points decrease from C to Sn but there is a slight increase from Sn to Pb. The boiling points first decrease from C to Si, then increase from Si to Ge and then again decrease from Ge to Pb.
(v) Electronegativity- Carbon, the first member of the family has a maximum value of electronegativity (2.5) in its group. On moving down the group from C to Pb, the electronegativity goes on decreasing due to an increase in atomic size and shielding effect of inner electrons.
(vi) Ionisation energy- Because of small atomic size than group 13 elements, the ionisation energy of group 14 elements are comparatively higher than group 13 elements. However, on moving down the group from C to Pb, the ionisation energy goes on decreasing due to an increase in atomic size and screening effect which overcomes the effect of increased nuclear charge.
(vii) Electropositive Character ( or Metallic Character)- The elements of group 14 show a very little tendency to lose their valence electrons because of their high ionisation energy and, hence, are less electropositive in character than corresponding elements of group 13. On moving down the group from C to Pb, electropositive character shows an increasing trend due to a decrease in ionisation energy. Carbon is typical non-metals, Si is a semi-metal, Ge is a metalloid whereas Sn and Pb are typical metals.
(viii) Oxidation States- The outer electronic configuration of these elements (ns2 np2) shows that they have an equal tendency of either gaining four electrons or losing four electrons to acquire stable electronic configuration. Due to high ionisation energy, these elements do not form stable M4+ ions and due to their low electron affinity, they are unable to from M4- ions. Therefore, these elements tend to share four electrons and form covalent compounds. These elements show oxidation states of +2 (using only p-electrons) and +4 (using both s and p-electrons). The +2 (using only p-electrons) and +4 (using both s and p electrons). The tendency to show +4 oxidation state decreases on moving down the group while that of +2 increases due to inert pair effect (i.e. resistance inertness of the outer s-electrons to take part in bonding). Thus Sn+2 and Pb+2 are more stable than Sn4+ and Pb4+.
(ix) Allotropy- Except Pb, other elements of group 14 exhibit the phenomenon of Allotropy (i.e. exist in more than one form having different physical properties but similar similar chemical properties). The allotropic forms of carbon are crystalline (graphite and diamond) and amorphous (coal, coke etc.). Silicon is amorphous and crystalline; Tin- grey tin, white tin, rhombic tin.
(x) Catenation- It is the property of an element to form a long chain of covalent bonds by linking with identical atoms. The property of catenation depends upon the atom-atom bond strength, i.e., higher the strength of atom-atom bond than atom-other atom bond, more will be the catenation. Carbon exhibit catenation to a maximum extent (60-atoms) due to its small size, high electronegativity and above all high c-c bond strength (353 KJ mole-1). On moving down the group, the extent of catenation decreases due to an increase in atomic size, decrease in electronegativity and atom-atom bond strength. Si shows catenation up to 6-atoms (225.7 KJ/mole-1); Ge up to 3-atoms (167.2 KJ/mole-1) and Sn up to 2-atoms (154.7 KJ/mole-1). Pb hardly shows any tendency of catenation.
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