CID 297

CH₄

Methane

Ball-and-stick Stick Space-filling

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5 atoms, 4 single bonds, tetrahedral.

IUPAC name: methane
Molar mass: 16.0430(28) g/mol
Atoms: 5
Shape: tetrahedral
Bond angle: about 109.5°
Polarity: nonpolar
SMILES: C
InChIKey: VNWKTOKETHGBQD-UHFFFAOYSA-N
PubChem CID: 297

Made of

Structural formula of methane. Every atom in the molecule is drawn. It shows which atoms are joined to which, not the shape. The model above shows the shape.

Bubbles rising from swamp mud and the flame of a Bunsen burner come from the same gas, whose other names include marsh gas and methyl hydride. Methane is an alkane, a hydrocarbon held together by single covalent bonds only, and it is built from one carbon atom and four hydrogen atoms. OpenStax calls it the fully reduced form of any one-carbon organic molecule.

The gas has no colour, odour or taste, and it boils at −161.5 °C. Methane is nonpolar, so its molecules attract one another only through dispersion forces, weak pulls that arise from brief, synchronised shifts of charge in neighbouring molecules. A smaller molecule is less polarisable, meaning its electron cloud distorts less easily, and its dispersion forces are weaker. That is why OpenStax expects CH₄ to have the lowest boiling point of the group 14 hydrides.

Structure and bonding

Methane has one carbon at the centre and a hydrogen at the end of each of its four single bonds. In the Ball-and-stick view the hydrogen atoms sit at the corners of a tetrahedron. VSEPR (valence shell electron-pair repulsion) theory explains why: four bonding pairs spread apart to minimise their repulsion, which gives a tetrahedral geometry. PubChem’s computed model puts 109.47° between every pair of bonds, matching the 109.5° OpenStax gives for a perfect tetrahedron. Turned with one bond pointing out of the screen, it shows the other three hydrogens as an even triangle.

The model draws the real bonding; methane has only one possible structure. OpenStax places carbon’s four valence electrons in four identical sp³ hybrid orbitals, mixed from one s and three p orbitals. Each overlaps a hydrogen 1s orbital in a sigma (σ) bond, giving four equivalent C–H bonds. The Stick view reduces them to four equal spokes from one hub, while the Space-filling view packs the hydrogen spheres against the carbon into a compact, rounded outline. Each C–H bond is slightly polar, but the identical bonds point symmetrically outward, so the molecule’s dipole moment is zero.

Where it turns up

Methane is the main ingredient of natural gas, drawn from underground natural gas fields and piped into homes for heating and cooking. Gas collected from coal mines is burned as fuel too. At the surface, decaying matter in swamps and marshes releases it.

The makers in the swamp are microbes. Methanogens, a group of archaeans (single-celled prokaryotes of the domain Archaea) found in soil and in the guts of ruminants such as cows and sheep, reduce carbon dioxide to methane. They do it to oxidise NADH, a molecule that carries electrons inside cells, when no oxygen is available.

The US Environmental Protection Agency (EPA) lists the emissions people cause: producing and transporting coal, natural gas and oil, livestock and other farming, land use, and waste rotting in landfills. That list covers human activity only, leaving out the wild wetlands and soils where methanogens work unmanaged.

Why it matters

Alkanes burn in oxygen in a highly exothermic redox reaction that gives carbon dioxide and water, which is why they make excellent fuels. For methane, OpenStax gives the enthalpy of combustion as −890.8 kJ per mole at 25 °C. A Bunsen burner works at the constant pressure of the atmosphere, so the heat it releases equals that enthalpy change. The same gas generates electricity and, in compressed form, runs vehicles. A fuel cell takes it through the same redox chemistry on a catalyst, without a flame and significantly more efficiently.

Chemical plants also use methane as a raw material. Its largest industrial use, according to the Hazardous Substances Data Bank (HSDB), is making synthesis gas, which combines hydrogen with carbon monoxide. That mixture is the main feedstock for ammonia and methanol. Methane is also a starting material for hydrogen cyanide, acetylene and formaldehyde, and a source of carbon black. US companies reported between 4 and 5.5 billion pounds of it to the EPA for 2023.

Properties

Properties of methane Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 297.
Property	Value	Unit	Source
Molecular formula (Hill order)	CH₄
Molar mass	16.0430(28) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	1
Hydrogen atoms	4
Bonds	4
PubChem molecular weight	16.043 g/mol	g/mol	PubChem

Safety

As a poison methane is practically inert, but the gas is not harmless. It is an extremely flammable gas, and under GHS, the Globally Harmonized System of hazard labelling, it carries the signal word Danger. At very high concentrations it displaces the oxygen in the air and causes suffocation, without warning in closed or confined areas, and evaporating liquefied methane causes frostbite. The PubChem Laboratory Chemical Safety Summary for methane is the authoritative sheet.

Questions

What shape is a methane molecule?

Tetrahedral. OpenStax finds four bonding electron pairs surrounding the carbon, and both the electron-pair geometry and the molecular structure are tetrahedral. In the Ball-and-stick view the carbon sits at the centre with a hydrogen atom at each corner of the tetrahedron. OpenStax describes carbon's four sp³ hybrid orbitals as pointing at 109.5° to one another, each forming one C–H bond. In PubChem's computed model every C–H bond is 1.092 Å long.

Is methane polar or nonpolar?

Nonpolar. Carbon is a little more electronegative than hydrogen, so each C–H bond is slightly polar, but four identical bonds arranged in a symmetric tetrahedron give a dipole moment of zero. Chloromethane shows the contrast: swapping one hydrogen for chlorine keeps the tetrahedral shape, yet its bond dipoles add up to a considerable dipole moment. Water dissolves only 22 mg of methane per litre at 25 °C, while ethanol, benzene and toluene dissolve it.

Is natural gas the same thing as methane?

Not quite. Natural gas is mostly methane, and for the gas supplied in the USA the Merck Index puts its share at 85 per cent. Commercial methane is separated from natural gas by absorption or adsorption, or made by fermenting cellulose and sewage sludge. Its sold grades run from technical, at 95 per cent, through chemically pure at 99 per cent to research grade at 99.99 per cent.

Is methane lighter than air?

The pure gas is. Its vapour density is 0.554 relative to air, and the Emergency Response Guidebook (ERG), the US Department of Transportation's guide for hazardous goods in transport, says leaking methane will rise. Vapour boiling off the liquefied gas behaves differently: the same guidebook says it starts out heavier than air and spreads along the ground. Which way a release travels therefore depends on whether it began as gas or as liquid.

Made of the same elements

C₂H₄ Ethylene 6 atoms, 5 bonds.
C₂H₂ Acetylene 4 atoms, 3 bonds.
C₂H₆ Ethane 8 atoms, 7 single bonds.
C₃H₆ Propylene 9 atoms, 8 bonds.
C₄H₆ 1,3-Butadiene 10 atoms, 9 bonds.
C₃H₈ Propane 11 atoms, 10 single bonds.
C₆H₆ Benzene 12 atoms, 12 bonds.
C₄H₁₀ Butane 14 atoms, 13 single bonds.

All 18 compounds made of carbon and hydrogen

C₄H₁₀ Isobutane 14 atoms, 13 single bonds.
C₇H₈ Toluene 15 atoms, 15 bonds.
C₈H₈ Styrene 16 atoms, 16 bonds.
C₅H₁₂ Pentane 17 atoms, 16 single bonds.
C₆H₁₂ Cyclohexane 18 atoms, 18 single bonds.
C₁₀H₈ Naphthalene 18 atoms, 19 bonds.
C₆H₁₄ Hexane 20 atoms, 19 single bonds.
C₈H₁₈ Isooctane 26 atoms, 25 single bonds.
C₁₀H₁₆ Limonene 26 atoms, 26 bonds.
C₈H₁₈ Octane 26 atoms, 25 single bonds.

Same shape (tetrahedral)

CCl₄ Carbon tetrachloride 5 atoms, 4 single bonds, tetrahedral.
CHCl₃ Chloroform 5 atoms, 4 single bonds, tetrahedral.
CCl₂F₂ Dichlorodifluoromethane 5 atoms, 4 single bonds, tetrahedral.
CH₂Cl₂ Dichloromethane 5 atoms, 4 single bonds, tetrahedral.
H₂SO₄ Sulfuric acid 7 atoms, 6 bonds, tetrahedral.

Appears in these articles

What holds atoms together: ionic, covalent and metallic bonds Table salt has no molecules in it; hydrogen chloride gas is nothing but molecules.
Intermolecular forces: why water boils at 100 °C and methane at −161 °C Methane's molar mass is 16 g/mol and water's 18, yet methane boils at −161 °C and water at 100 °C.
Why water is bent and carbon dioxide is straight: the VSEPR model Water's two bonds meet at 104.5°; carbon dioxide's lie in a straight line.