Chapter 4: Carbon and its Compounds

Chapter learning goals: Understand the core concepts, explain key processes, interpret diagrams and apply the ideas to board-style questions.

1. Why carbon forms so many compounds

Carbon has atomic number 6 and electronic configuration 2,4. It has four valence electrons. Losing four electrons would require enormous energy and gaining four would make a highly unstable C⁴⁻ ion. Carbon therefore shares electrons and forms covalent bonds. Its exceptional versatility comes from tetravalency (four covalent bonds) and catenation (strong carbon–carbon bonding that allows chains, branches and rings). Silicon also shows catenation but less strongly.

2. Covalent bonds and structures

A covalent bond is formed when atoms share electron pairs to achieve stable outer shells. Methane (CH₄): carbon shares one pair with each of four hydrogen atoms. In ethane (C₂H₆), the C–C single bond permits rotation; ethene (C₂H₄) has a double bond; ethyne (C₂H₂) has a triple bond. Covalent compounds generally have low melting/boiling points and do not conduct electricity because they lack free ions. Exceptions exist, so describe these as common trends.