Methane (CH4)

Summary: Methane (CH₄) is a tetrahedral covalent molecule in which carbon shares one electron pair with each of four hydrogen atoms, giving carbon an octet and each hydrogen a duplet; it is the simplest alkane, the main constituent of natural gas, and burns completely to carbon dioxide and water. Tags: igcse chemistry Created: 2026-07-18

Methane (CH₄) is a Compound of carbon and hydrogen and the standard IGCSE example of a Molecule with four single covalent bonds. A carbon atom (electronic configuration 2,4) has four outer electrons and needs four more to reach the octet of neon (see Group 0 Noble Gases); each hydrogen atom needs one more electron to reach the helium duplet. These requirements are satisfied when carbon shares one pair of electrons with each of four hydrogen atoms, forming four identical C—H bonds arranged tetrahedrally around the carbon so the bonding pairs are as far apart as possible. Methane is the first and simplest member of the Alkanes, the homologous series of saturated hydrocarbons with general formula CₙH₂ₙ₊₂. It is the main constituent of natural gas, one of the fossil fuels covered in Fuels and Petroleum, and its combustion supplies heat for homes and industry while its release to the atmosphere makes it a significant greenhouse gas (see Climate Change and Greenhouse Gases).

Bonding: Dot-and-Cross Description

In the Dot-and-Cross Diagram of CH₄, carbon’s 4 outer electrons are drawn as dots and each hydrogen’s single electron as a cross:

• Carbon contributes 1 electron to each of four shared pairs; each hydrogen contributes its 1 electron to one pair.
• The molecule has 4 bonding pairs — each shown as one dot + one cross between C and an H.
• There are no lone pairs on any atom: all 8 outer electrons are in bonds.
• Counting shared electrons, carbon has 8 outer electrons (octet) and each hydrogen has 2 (duplet).

Because the four bonding pairs repel each other equally, they spread out into a tetrahedral arrangement with H—C—H angles of about 109.5°.

Key Data

Physical Properties

• Colourless, odourless gas (the smell of domestic gas is an added odorant for safety).
• Simple molecular substance with very low melting and boiling points — only a weak Intermolecular Force acts between molecules, while the C—H bonds themselves are strong.
• Insoluble in water; less dense than air.
• Non-conductor of electricity — no ions or delocalised electrons.

Combustion and Uses

Methane is the main constituent of natural gas, a fossil fuel (see Fuels and Petroleum). In a plentiful supply of air it undergoes complete combustion:

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)

The reaction is strongly exothermic (see Energetics of Reactions), which is why methane is used for heating and cooking and in power stations. In a limited air supply, incomplete combustion produces toxic carbon monoxide (CO) and soot (C) — a hazard covered under Air Pollution.

Other points:

• As an alkane, methane is generally unreactive except for combustion and its substitution reaction with chlorine in UV light (see Alkanes).
• Methane is itself a potent greenhouse gas, released from livestock, rice paddies and landfill (see Climate Change and Greenhouse Gases).
• Industrially, methane and steam are used to make the hydrogen needed for the Haber process.

Sources

• Cambridge IGCSE Chemistry 0620 Syllabus (2023-2025) — Section 2.5, Cambridge Assessment International Education

Common Misconceptions