Carbon Family & Compounds
Inorganic Chemistry – WBJEE Study Notes
1. Simple Explanation
The carbon family (Group 14 of the periodic table) contains C, Si, Ge, Sn, and Pb.
- Carbon is the only non‑metal that can form stable covalent bonds with itself, giving rise to the most versatile and abundant class of compounds in chemistry.
- In inorganic chemistry, we focus on carbon’s role as an element: its allotropes, oxidation states, and its ability to form simple inorganic compounds such as oxides, carbides, cyanides, and carboxylates.
- Carbon, unlike the heavier congeners, can reach all five oxidation states (−4, −2, 0, +2, +4) and can also act as a ligand in coordination complexes (e.g., CO, CN⁻, isocyanide).
2. Key Points
| Aspect | Details |
|---|---|
| Atomic & Physical Properties | • Atomic number 6, electronegativity 2.55 (most electronegative element). • Forms all four allotropes: diamond, graphite, graphene, fullerenes. |
| Oxidation States | +4 (most stable), +2, 0 (in elemental form), –2 (in hydrides), –4 (in methane). |
| Common Inorganic Compounds | • Oxides – CO, CO₂, C₂O₄²⁻ (oxalate). • Hydrides – CH₄, SiH₄, GeH₄, SnH₄. • Carbides – CaC₂, Na₂C₂ (alkali metal acetylides). • Cyanides & Isocyanides – CN⁻, NCO⁻. • Carbonates & Bicarbonates – CO₃²⁻, HCO₃⁻. • Carboxylates – RCOO⁻ (acetate, formate). |
| Coordination Chemistry | • Metal carbonyls – Fe(CO)₅, Ni(CO)₄. • Cyanide complexes – [Fe(CN)₆]³⁻, [Au(CN)₂]⁻. • Isocyanide complexes – [M(CNC)₂]⁺. |
| Reactivity Trends | • Carbon’s ability to form multiple bonds leads to high reactivity (e.g., CO₂ is inert but reacts in Fischer–Tropsch). • Si, Ge, Sn, Pb form silanes, germanes, stannanes (analogous to hydrocarbons but less stable). |
| Environmental & Biological Relevance | • CO₂ is a greenhouse gas; carbonates are important in geology and biology. • Cyanides are toxic ligands; their complexes are studied in bioinorganic chemistry. |
3. Worked Example
Problem:
Determine the oxidation state of carbon in the complex Fe(CO)₅ and verify that the sum of oxidation states equals the charge on the complex.
Solution:
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Assign known oxidation states:
- Iron (Fe) in a neutral complex has oxidation state 0 (since the complex is neutral).
- CO is a neutral ligand (neutral molecule). In metal carbonyls, CO is a neutral ligand, so it contributes 0 to the overall charge.
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Write the overall charge balance: [ \text{Oxidation state of Fe} + 5 \times (\text{Ox. state of CO}) = 0 ] [ 0 + 5 \times 0 = 0 ]
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Check oxidation state of carbon:
- In CO, carbon is bonded to oxygen with a double bond and to iron with a dative bond. However, as a ligand, CO is