Ethane

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8 atoms, 7 single bonds.

IUPAC name: ethane
Molar mass: 30.0700(52) g/mol
Atoms: 8
SMILES: CC
InChIKey: OTMSDBZUPAUEDD-UHFFFAOYSA-N
PubChem CID: 6324

Made of

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

Mixed into natural gas alongside methane is ethane, a gas that the petrochemical industry turns mainly into ethylene and from there into plastics. HSDB (the Hazardous Substances Data Bank) puts it at about 9 per cent of natural gas. Its share of the gas fraction of petroleum runs from 1 to 13 per cent in HSDB’s figures, beside 83 to 99 per cent methane.

Setting n to 2 in the alkane formula C_nH_2n+2 gives C₂H₆: two carbon atoms and six hydrogen atoms, 30.07 g/mol. Its IUPAC name is simply ethane. In Chem1’s naming scheme, eth- is the prefix for two carbons and the ending -ane marks an alkane.

Haz-Map, an occupational health database, describes ethane as a colourless, odourless gas. HSDB gives its boiling point as −88.6 °C, and the International Chemical Safety Card gives −89 °C. Water takes up only 60.2 mg of it per litre at 25 °C, while benzene dissolves it very readily.

Structure and bonding

The readout counts 8 atoms and 7 single bonds. With Labels on, two C atoms sit at the centre, each carrying three H. In Chem1’s description each carbon bonds to four atoms, three hydrogens plus its partner, and is tetrahedrally coordinated. The Ball-and-stick view shows those bonds fanning out toward a tetrahedron’s corners, at 108.3° for H–C–H and 110.6° for H–C–C in PubChem’s computed model.

Turned so the C–C bond points straight at the viewer, the model shows the front hydrogens set between the back ones, two tripods offset by a sixth of a turn. The computed model fixes this one arrangement, with H–C–C–H angles of 60° and 180°. Its C–C bond is 1.512 Å long, each C–H bond 1.094 Å.

Every drawn bond is single, as in the real molecule. In Chem1’s hybrid orbital account, each carbon’s orbitals, the regions where its electrons are likely to be found, mix into four sp³ orbitals aimed at a tetrahedron’s corners. One on each carbon overlaps its partner’s to form the C–C bond. The remaining ones overlap hydrogen 1s orbitals in the six C–H bonds. Stick shows a rod with three spokes at each end, and Space-filling a compact lump.

Where it turns up

HSDB places ethane in natural gas, in crude oil and in refinery gases. It also forms when hydrocarbons are cracked by heat or with hydrogen, and when coal is liquefied. Bottled gas, by Haz-Map’s figures, is about 5 per cent ethane, 5 per cent butane and 90 per cent propane.

Ethane that processors leave in the gas flows on through the interstate pipeline system. So, according to the US Energy Information Administration (EIA), every American household or plant burning natural gas burns some ethane along with it. It is also listed as a propellant in cosmetics.

Living things make it too. The LOTUS natural-products database reports ethane in hops (Humulus lupulus), Aster scaber and Syzygium cumini, and ChEBI, a dictionary of biologically relevant molecules, gives it the role of plant metabolite. In rats, lipid peroxidation, the breakdown of fats by oxidation, releases ethane as an end product, and the animals breathe it out largely unchanged.

Why it matters

Steam cracking to ethylene is, by HSDB’s account, the single most important industrial use of ethane. The EIA says that ethylene feeds a range of intermediate chemicals, most of them later converted into plastics. Ethane is also a feedstock, or raw material, for vinyl chloride and other chlorinated compounds, a refrigerant in some two-stage systems, and a fuel for power generation. The US Environmental Protection Agency (EPA) Chemical Data Reporting puts the aggregate US production volume for 2023 at 120 to 130 billion pounds.

US consumption of ethane has grown because of its larger supply and its lower cost than other petrochemical feedstocks, according to the EIA. Supply has to track demand closely, the EIA explains, since demand sits almost entirely with petrochemical plants and the gas is hard to move except in dedicated pipelines. Processors sometimes choose not to recover it, a practice called ethane rejection. The ethane left behind raises the heat value of pipeline gas above methane’s, which the EIA puts near 1,010 British thermal units (Btu) in a standard cubic foot.

Properties

Properties of ethane Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 6324.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₂H₆
Molar mass	30.0700(52) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	2
Hydrogen atoms	6
Bonds	7
PubChem molecular weight	30.07 g/mol	g/mol	PubChem

Safety

Ethane is an extremely flammable gas, and its GHS (Globally Harmonized System) classification carries the signal word Danger. Haz-Map rates it practically inert as a poison, yet in confined spaces it displaces oxygen and can bring dizziness or asphyxiation without warning. Its liquid causes frostbite, and the PubChem Laboratory Chemical Safety Summary for ethane is the full hazard sheet.

Questions

What shape is an ethane molecule?

No one shape word fits ethane, since it has two carbon centres rather than a single central atom. Chem1 describes each carbon as tetrahedrally coordinated, bonded to three hydrogens and to the other carbon. In the viewer's computed model the angles around each carbon measure about 108° to 111°, and the six C–H bonds point away from the C–C axis with three on each side of the bond.

What is ethane used for?

Most ethane becomes ethylene, which the US Energy Information Administration (EIA) says is made into intermediate chemicals, most of them later plastics. In US crackers ethane is a feedstock, or raw material, alongside propane and naphtha, according to the EIA. HSDB (the Hazardous Substances Data Bank) lists it as a refrigerant in two-stage systems where relatively low temperatures are produced, and Haz-Map lists it as a fuel gas.

Where does ethane come from?

Ethane is extracted from natural gas at gas processing plants, or from crude oil during refining, according to the EIA. Fractionation plants then split the mixed liquids into purity products, ethane among them, each at least 90 per cent one kind of molecule. HSDB also records ethane forming when hydrocarbons are cracked with heat or hydrogen, and when coal is liquefied.

Is ethane dangerous to breathe?

As a poison it does little: Haz-Map calls ethane practically inert. The danger is what it pushes aside. In an enclosed space the gas can crowd oxygen out of the air, and dizziness or suffocation can follow without warning, as the Emergency Response Guidebook puts it. It is also an extremely flammable gas. Vapour from the liquefied gas is at first heavier than air and spreads along the ground, and rapidly evaporating liquid may cause frostbite.

Made of the same elements

C₃H₆ Propylene 9 atoms, 8 bonds.
C₄H₆ 1,3-Butadiene 10 atoms, 9 bonds.
C₂H₄ Ethylene 6 atoms, 5 bonds.
CH₄ Methane 5 atoms, 4 single bonds, tetrahedral.
C₃H₈ Propane 11 atoms, 10 single bonds.
C₂H₂ Acetylene 4 atoms, 3 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.