Group 14 Elements

In this part we will have a brief view about group 14 elements. This part will see the occurrence of group 14 elements, the chemical properties (1st ionisation energy and electron affinity, covalent radius, and Pauling electronegativity scale), the physical properties (melting and boiling point), the allotropes, and the compounds of group 14 elements (the oxidation states, oxides, and chlorides). 

From left to right: carbon, silicon, germanium, tin, and lead

Occurrence

Table 1. The abundances of Group 14 element

The earth’s crust Si has the highest occurrence due to most of the minerals of the earth’s crust are silicate mineral (contain Si). In the other sides, general decreasing pattern of the abundance at the universe proves the theory of the origin of the universe. C exists at earth’s crust as two main allotropes, diamond and graphite⁴. However, amorphous C and fullerenes (Australia, New Zealand, North America⁴) also could be found as well. Ge could be found as traces in minerals, Sn and Pb could be found mainly in their principal mineral⁴.

Extraction

Natural graphite are increased the quality by heating powdered coke with silica at high Temperature⁴. Diamonds could be synthesised chemical vapour deposition and hydrothermal processes⁴. Amorphous C is synthesised by burning oil in limited air supply⁴. Si is extracted from SiO₂ by heating with C or CaC₂ in electric furnace⁴. Ge is extracted as trace of Zn mineral or reducing from GeO₂ with H₂ or C⁴. Sn is extracted from reduction of SnO₂ with C⁴. Pb can be extracted as shown at the reaction below⁴:

 or

The Chemical and Physical Properties

Table 1. The Chemical & Physical Properties of Group 14 Elements

	IE1/ kJ mol-1	Covalent radius/ pm	Melting Point/ K	Boiling point/ K	χP	1st EA/ kJ mol-1
C	1086	77	3823	5100	2.55	153.9
Si	786.5	118	1687	2628	1.90	133.6
Ge	762.2	122	1211	3106	2.01	119.0
Sn	708.6	140	505	2533	1.96	107.3
Pb	715.6	154	600	2022	2.33	35.1

General decreasing down the group due to valence electron fills higher energy level. High IE₁ of C due to its small radius. A small increase of IE₁ of Pb due to it starts to fill f-orbital and relativistic effect. This reason also can be applied to the electronegativity. In addition, increasing from Si to Ge due to d-orbital is occupied, but provides less shielding effect, χ^p of Ge is higher than χ^pSi. For 1^st electron affinity, it decreases down the group, due to shielding effect due of core electron. Sharp decreasing to Pb could be caused by the occupied f-orbital and relativistic effect. Increasing trend down the group is due to the valence electrons occupy higher energy level and there is shielding effect from core electrons.

The trend of melting and boiling point is related to the structure of the elements. The melting and boiling point of carbon is for diamond. C, Si, and Ge adopt the diamond structure, so decreasing melting point due to weaker bonding that caused by the covalent radius. In the other sides, Sn and Pb adopt the metallic solid structure which is bound by delocalised electron. The strength of metallic bond is related with the first ionisation energy.

 

The Compounds

a.       Catenation and Allotropes

Carbon allotropes (graphite crystal on the left side)

Catenation is the ability of an element to make covalent bond with themselves⁵ and this ability decreases down the group. Meanwhile, Allotrope is an element that can have different structure. C has many allotropes, mainly it exist as graphite and diamond. Besides that, Sn also has allotropes as α-tin which turn into β-tin at 13^oC, and turn into γ-tin at 161^oC⁵.

b.      The oxidation states

Group 14 elements can have +2 and +4 oxidation states, and the stability of compound +4 oxidation states increases down the group. C,Si, Ge, and Sn compounds are stable at +4 oxidation states, while Pb compound is stable at +2 oxidation states. All group 14 elements are covalent, except Pb(II) and Sn(II)⁵.

c.       Oxides

C have stable monomeric compound CO and CO₂. CO is almost insoluble in water under normal condition and does not react with NaOH, at high pressure and temperatures HCOOH and NaHCOO are formed. CO₂ could dissolve in water to provide weakly acid solution of CO₂.

The transition SiO₂ of in different temperature

SiO₂ is the only stable silicon oxide compound and it has acidic properties.SiO₂ slowly dissolve in strong base to produce orthosilicate (SiO₄^2-)or metasilicate (SiO₃^2-)⁶.

Quartz crystal structure (left) and rutile crystal structure (right)

GeO₂ has similar structure with SiO₂, quartz and rutile crystal. GeO₂ dissolve in concentrated HCl forming [GeCl₆]^- and form GeO₄^2- if dissolve in alkali. GeO also exists and is amphoteric, and it disproportionates at high temperature⁴.

Solid SnO₂ and PbO₂ has rutile structure crystal. SnO₂ is soluble in acids, but also has amphoteric character. In the other sides, PbO₂ shows acidc properties and produce [Pb(OH)₆]^2-. SnO and PbO are amphoteric compounds⁴.

d.      Chlorides  

      The chloride compounds of group 14 react with water, except CCl₄. SiCl₄ reacts with water to produce SiO₂ and HCl. Ge has two chloride compounds GeCl₄ and GeCl₂⁴. GeCl₂ disproportionates when it is heated⁴.

References

¹ M. Winter, Abundance in Earth’s Crust, http://www.webelements.com/periodicity/abundance_crust/group_14.html, accessed 10/10/12.

² M. Winter, Abundance in oceans, http://www.webelements.com/periodicity/abundance_seawater/group_14.html, accessed 10/10/12.

³ M. Winter, Abundance in the universe, http://www.webelements.com/periodicity/abundance_universe/group_14.html, accessed 10/10/12.

⁴ C.E. Housecroft and A.G. Sharpe, Inorganic Chemistry, Pearson, Essex, 2012, 4^th ed., ch. 14.

⁵ R. Lewis and W. Evans, Chemistry, Pelgrave Macmillan, London, 2011, 4^th ed., pp. 198 – 212.

⁶ R.H. Petrucci, F.G. Herring, J.D. Madura, and C. Bissonette, General Chemistry: Principles and Modern Applications, Pearson, Toronto, 2011, 10^th ed., p. 959.