Nitrous oxide

Ball-and-stick Stick Space-filling

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3 atoms, 2 bonds.

IUPAC name: nitrous oxide
Molar mass: 44.0130(30) g/mol
Atoms: 3
SMILES: [N-]=[N+]=O
InChIKey: GQPLMRYTRLFLPF-UHFFFAOYSA-N
PubChem CID: 948

Made of

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

Dentists and surgeons know nitrous oxide as laughing gas, and Haz-Map records its use as an anaesthetic since 1844. Each molecule joins two nitrogen atoms to one oxygen atom, with the oxygen at one end rather than in the middle. The gas has a slightly sweet odour and boils at −88.48 °C. In a cylinder at room temperature it is held as gas over liquid, at a pressure of about 800 pounds per square inch.

At ordinary temperatures the Hazardous Substances Data Bank (HSDB) calls it very stable and rather inert chemically. Heat changes that. Above 300 °C the molecule begins to dissociate, and the International Chemical Safety Cards then class it as a strong oxidant. OpenStax lists it, with carbon monoxide and nitric oxide, among the few nonmetal oxides that are not acidic.

Structure and bonding

The viewer holds three atoms and two bonds, and the three atoms sit on one straight line. With Labels switched on, the symbols read N, N, O from one end to the other, so oxygen is terminal. Formal charge, a bookkeeping count of electrons that does not indicate real charges on the atoms, favours that order, OpenStax says.

In Ball-and-stick, a triple bond joins the two nitrogens and a single bond links the second nitrogen to oxygen. Stick trims the atoms away and leaves one straight rod, triple at one end and single at the other. Space-filling merges the three spheres into a short, blunt rod with no bend.

That drawing is one Lewis structure, a diagram of the bonds and lone electron pairs, out of two. The SMILES string in the facts list, a one-line text code for the structure, writes the second form, with two double bonds. The real electron distribution is an average of the forms and never flips between them. HSDB gives its dipole moment, the measure of net charge separation across the whole molecule, as 0.166 debye.

Where it turns up

One HSDB entry sums up its main jobs: an anaesthetic in dental and surgical work, pushing food out of aerosol cans, and finding leaks. OpenStax adds the routine extraction of wisdom teeth. The medical mixture Entonox, in HSDB’s description, is nitrous oxide and oxygen in equal parts. Haz-Map notes its use as a foaming agent for whipped cream. The food-additive committee of the Food and Agriculture Organization and the World Health Organization (WHO) files it as a foaming agent, propellant and antioxidant. US industry reporting also lists it as a semiconductor and photovoltaic agent and as an etching agent.

Away from clinics and kitchens it is a greenhouse gas. The US Environmental Protection Agency (EPA) overview names human sources: agriculture, land use, industry, burning fossil fuels and solid waste, and treating wastewater. That list is not the whole story. The EPA’s climate basics page adds natural biological processes.

Why it matters

The WHO lists nitrous oxide among general anaesthetics on its Model Lists of Essential Medicines. HSDB states that 99.9 per cent of the absorbed gas leaves unchanged. It calls the gas poorly soluble in blood, with a low blood/gas partition coefficient, and says most of the gas leaves rapidly through the lungs.

How it relieves pain is not settled. DrugBank describes opioid peptides released in the brain stem, switching on nerve cells that signal downward with noradrenaline. It adds that several other receptor types have been implicated. HSDB puts the pain relief down to a direct action inside the spinal cord. It also notes altered opioid and serotonin receptors, but calls the receptors behind its brain effects unclear.

The UCAR Center for Science Education, a US climate-science teaching site, says greenhouse molecules have three or more atoms and vibrate when they absorb heat. UCAR names nitrous oxide beside carbon dioxide, water vapour and methane. HSDB puts its global warming potential, the EPA’s measure of the heat a tonne of gas absorbs relative to carbon dioxide, at 298 over 100 years.

Properties

Properties of nitrous oxide Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 948.
Property	Value	Unit	Source
Molecular formula (Hill order)	N₂O
Molar mass	44.0130(30) g/mol	g/mol	IUPAC/CIAAW 2024
Nitrogen atoms	2
Oxygen atoms	1
Bonds	2
Single bonds	1
Triple bonds	1
PubChem molecular weight	44.013 g/mol	g/mol	PubChem

Safety

Nitrous oxide carries the signal word Danger, first as an oxidiser that may cause or intensify fire. Its cylinders hold gas under pressure, the liquid may cause frostbite, and the gas is heavier than air, so it can gather in low spaces and leave too little oxygen. HSDB links long workplace exposure to weakened vitamin B₁₂ function and poorer reproductive health, and Haz-Map records nerve damage from misuse. The PubChem Laboratory Chemical Safety Summary and the NIOSH card (US National Institute for Occupational Safety and Health) give the full guidance.

Questions

Is laughing gas the same as nitrous oxide?

Yes. The Pocket Guide of the US National Institute for Occupational Safety and Health lists laughing gas as a synonym, together with dinitrogen monoxide and hyponitrous acid anhydride. The CAMEO Chemicals entry says the gas has narcotic effects when inhaled. The Hazardous Substances Data Bank warns that it should not be confused with the poisonous and irritating oxides of nitrogen, which are different compounds.

Why is the oxygen at the end of the nitrous oxide molecule?

Formal charge explains it, OpenStax says: a bookkeeping count of the electrons each atom owns in a Lewis structure. The arrangement N–N–O best meets the rules for a stable spread of formal charge: the negative formal charge lands on oxygen, the more electronegative element, and the less electronegative nitrogen takes the centre. The alternative with oxygen in the middle fits those rules worse.

Does nitrous oxide help things burn?

Only when hot. At room temperature the Hazardous Substances Data Bank calls the gas very stable and rather inert. Heated, it decomposes into nitrogen and oxygen, and OpenStax explains the result: one-third of the gas released is oxygen, against one-fifth in air, so it supports combustion better than air does. The US CAMEO Chemicals database calls it a weak oxidising agent, while the International Chemical Safety Cards call it a strong oxidant above 300 °C.

Why does nitrous oxide expand air pockets in the body?

The Hazardous Substances Data Bank gives the reason: the gas dissolves 35 times more readily than nitrogen does. During anaesthesia it exchanges with nitrogen and diffuses into hollow organs and body spaces, which enlarges any trapped air. The reverse happens when the gas is switched off: it floods back into the lungs, dilutes the air there and can lower the oxygen available.