Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 110	General Chemistry	Fall 2003
Lecture Notes::Lec 27_3 November	© R. Paselk 2003
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The Chemistry of the Elements

The Representative Elements

Group IV

Chemistry

Group IV shows a vary obvious transition from a non-metal to increasingly metallic elements going down the group, ending in true metals.

• Carbon is a classic example of a non-metal.
• Silicon and Germanium are semi-metals.
• Tin and Lead are metals.

Group IV give perhaps the most obvious example of the difference in properties between elements of Period 2 and higher Periods, since carbon, as a very distinct non-metal, behaves much differently than any of the other Group IV members.

The elements from silicon to lead show a nice transition of properties towards increasingly metallic.

The group shows an obvious "inert pair effect" with silicon and germanium exhibiting the +4 oxidation state, while Tin and lead exhibit both +2 and +4 oxidation states

Properties of Group IV

Property		C	Si	Ge	Sn	Pb
Outer electron configuration		2s2p2	3s2p2	4s23d104p2	5s24d105p2	6s24f145d106p2
Melting point (°C)		3550 (dia)	1410	938	505	601
Density (g/cm3)		2.25 (graph)	2.33	5.35	7.28	11.3
Ionization energies - 1st & sum of 1-4 (kJ/mol) M(s) Æ M4+(aq) + 4 e-		1086 14,280	787 9,947	762 10,000	709 8,988	715 9,325
Standard Reduction Potentials (V, 25°C) M2+(aq) + 2 e- Æ M(s)		-	-	-	-0.138	-0.126
Electronegativity		2.5	1.8	1.8	1.8	1.8

• Carbon
  • Very abundant in both elemental and combined form in Earth's crust. Three Allotropes (different physical forms of the same element)
    • Diamond: colorless (when pure) cubic or octahedral crystals (often have curved edges and faces due to lattice defects). Diamond is a non-conductor of electricity since all valence electrons involved in covalent bonds
    • Graphite is electrically conductive, and has a semi metallic luster, so has a bit of metal character!
    • Fullerenes
  • +4 and -4 oxidation states
  • One of only two elements with highly stable and strong single, double, and triple bonds.
  • Important inorganic compounds of C include CO, CO₂, CN, carbonates, cyanides, and carbides
    • Various carbides are important as abrasives and cutting tools (silicon carbide, tungsten carbide, etc.)
  • Infinite number of carbon based compounds due to very strong and stable C-C bonds.
• Silicon. Crystallizes as the pure element in a diamond lattice, forming a hard, brittle, high-melting solid with a metallic luster, but low conductivity. It is THE base of the modern semi-conductor industry.
  • Chemistry is dominated by the chemistry of the +4 oxidation state.
    • Silicon can form binary compounds with hydrogen (Silanes, SiH₄, Si₂H₆, etc.) and halogens (SiCl₄) but these compounds tend to react with oxygen to give silicon dioxide, SiO₂.
    • Most silicon compounds are based on silicon dioxide and silicates.
    • Unlike carbon, silicon does not form double bonds with oxygen, rather it forms compounds with sp³ hybridization and four oxygens arranged tetrahedrally around the silicon.
      • The simplest is SiO₄^-, orthosilicate.
        • The acid of orthosilicate is only stable in very dilute solution, polymerizing as it concentrates.
        • The orthosilicate ion is found in a few minerals such as: olivine ( Mg₄SiO₄) and zircon (ZrSiO₄)
      • Extended silicate ions are called metasilicates. Note that in each case the silicon is again bonded tetrahedrally to four oxygens.
        • The simplest metasilicate is the "infinite" linear chain, SiO₃^2-.
          • Minerals based on linear metasilicate are known as pyroxenes, and include jadeite, NaAl(SiO₃)₂. The metasilicate chains are held together adjacently by the cations bridging the charged oxygens in these minerals.

© R A Paselk

Last modified 4 November 2003