Carbon and the Chemistry of Life

Carbon has four electrons in its outer shell — exactly half-full — so sharing four electrons is far easier than giving away or grabbing four.

A tetrahedron, with bond angles of roughly 109.5°, making every carbon atom a three-dimensional four-way junction box.

Si–Si bonds are weaker (~222 kJ/mol vs ~348 kJ/mol for C–C), silicon forms double bonds poorly, and its oxide SiO₂ is solid sand rather than an exhalable gas like CO₂.

Molecules with the same formula but different structural arrangements — e.g. glucose and galactose are both C₆H₁₂O₆ but the body treats them as different sugars. Isomerism gives chemistry near-infinite specificity.

A small cluster of atoms bolted onto a carbon skeleton that behaves predictably wherever it appears, providing the reactivity a plain hydrocarbon chain lacks.

Carboxyl (–COOH) is acidic, donating a proton to become –COO⁻; amino (–NH₂) is basic, accepting a proton to become –NH₃⁺.

It carries both a carboxyl group (which loses a proton) and an amino group (which gains one), so it has positive and negative charges simultaneously.

Condensation removes a water molecule to form the bond; hydrolysis adds water back to split it.

Two sulfhydryl groups can link to form a disulfide bridge, stapling a protein into its shape.

C₆H₁₄ has 5 structural isomers; C₁₀H₂₂ has 75; C₂₀H₄₂ has over 366,000 — complexity explodes with chain length.