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Group 14 (C, Si, Ge, Sn, Pb) has ns^{2np}^2. Carbon dominates through catenation (C-C = 348 kJ/mol, strongest) and ppi-ppi multiple bonding (unique to C among Group 14).
Carbon allotropes: diamond (sp3, hardest, insulator), graphite (sp2, conductor, lubricant), fullerene C60 (12 pentagons + 20 hexagons), graphene (single layer, extraordinary properties). CO2 is a discrete linear molecule (ppi-ppi bonding); SiO2 is a 3D network solid (Si can't form pi bonds).
Silicon differs from carbon critically: SiCl4 is hydrolysed (vacant 3d orbitals allow H2O attack) while CCl4 is not (no d-orbitals = no pathway). Si forms strong Si-O bonds, creating silicates and silicones. Silicones (R2SiO)n are versatile polymers with Si-O backbone.
The inert pair effect dominates Group 14 chemistry below Si: Sn shows both +2 and +4 (SnCl2 is a reducing agent), but Pb strongly favours +2 (PbO2 is a powerful oxidising agent, PbCl4 decomposes at RT). The lead-acid battery exploits PbO2's oxidising ability.
CO is isoelectronic with N2, toxic (binds haemoglobin), and a versatile ligand. Water gas (CO + H2) is produced from C + H2O at high temperature.