[10102-44-0][1]

Nitrogen dioxide
General
Molecular formula	NO2
Molar mass	46.01 g/mol
Appearance	brown gas
Properties
Density and phase	see text
Solubility in water	reacts
Melting point	see text
Boiling point	see text
Structure
Molecular shape	bent
Dipole moment	? D
Thermodynamic data
Std enthalpy of formation ΔfHo298	+33.10 kJ/mol
Standard molar entropy So298	240.04 J·K−1·mol−1
Hazards
MSDS	External MSDS
EU classification	Highly toxic (T+)
NFPA 704
R-phrases	R26, R34
S-phrases	S1/2, S9, S26, S28, S36/37/39, S45
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Related nitrogen oxides	Nitrous oxide Nitric oxide Dinitrogen tetroxide Dinitrogen pentoxide
Related compounds	Nitric acid Nitrous acid
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

The chemical compound nitrogen dioxide (NO₂) is a reddish or orange/brown gas with a characteristic sharp, biting odor. It is one of the most prominent air pollutants and a deadly poison by inhalation. A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... Molar mass is the mass of one mole of a chemical element or chemical compound. ... Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... A substance is soluble in a fluid if it dissolves in that fluid. ... A girl in a swimming pool Water (from the Old English waeter; c. ... The melting point of a solid is the temperature at which it changes state from solid to liquid. ... The boiling point of a substance is the temperature at which it can change its state from a liquid to a gas throughout the bulk of the liquid. ... four sp³ orbitals three sp² orbitals In chemistry, hybridisation is the mixing of atomic orbitals belonging to a same electron shell to form new orbitals suitable for the qualitative description of atomic bonding properties. ... The Earths magnetic field, which is approximately a dipole. ... The debye (symbol: D) is a non-SI and non-CGS unit of electrical dipole moment. ... The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at 1 atmosphere... In chemistry, the standard molar entropy is the entropy content of one mole of substance, under conditions of standard temperature and pressure. ... A material safety data sheet or MSDS is a form containing data regarding the properties of a particular substance. ... Council Directive 67/548/EEC of 27 June 1967 on the approximation of laws, regulations and administrative provisions relating to the classification, packaging and labelling of dangerous substances (as amended) is the main source of European Union law concerning chemical safety. ... NFPA 704 is a standard maintained by the U.S. National Fire Protection Association. ... Image File history File links File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... R-phrases are defined in Annex III of European Union Directive 67/548/EEC: Nature of special risks attributed to dangerous substances and preparations. ... S-phrases are defined in Annex IV of European Union Directive 67/548/EEC: Safety advice concerning dangerous substances and preparations. ... The refractive index of a material is the factor by which the phase velocity of electromagnetic radiation is slowed relative to vacuum. ... The dielectric constant εr (represented as or K in some cases) is defined as the ratio: where εs is the static permittivity of the material in question, and ε0 is the vacuum permittivity. ... Ultraviolet-Visible Spectroscopy or Ultraviolet-Visible Spectrophotometry (UV/ VIS) involves the spectroscopy of photons (spectrophotometry). ... IR spectrum of a thin film of liquid ethanol. ... Nuclear Magnetic Resonance Spectroscopy most commonly known as NMR Spectroscopy is the name given to the technique which exploits the magnetic properties of nuclei. ... It has been suggested that Mass spectrum be merged into this article or section. ... The term nitrogen oxide is imprecise and can be used to refer to any of these oxides (oxygen compounds) of nitrogen, or to a mixture of them: Nitric oxide (NO), nitrogen(II) oxide Nitrogen dioxide (NO2) Dinitrogen monoxide (N2O) (Nitrous oxide) Dinitrogen trioxide (N2O3) Dinitrogen tetroxide (N2O4) Dinitrogen pentoxide (N2O5... Nitrous oxide, also known as dinitrogen oxide or dinitrogen monoxide, is a chemical compound with chemical formula N2O. Under room conditions, it is a colourless non-flammable gas, with a pleasant, slightly-sweet odor. ... The chemical compound nitric oxide is a gas with chemical formula NO. It is an important signaling molecule in the body of mammals including humans, one of the few gaseous signaling molecules known. ... Nitrogen tetroxide (or dinitrogen tetroxide) (N2O4) is a hypergolic propellant often used in combination with a hydrazine-based rocket fuel. ... Dinitrogen pentoxide is the binary nitrogen oxide N2O5, also known as nitrogen pentoxide. ... R-phrases , S-phrases , , , , Flash point not applicable RTECS number QU5775000 Supplementary data page Structure and properties n, εr, etc. ... Nitrous acid weak monobasic acid known only in solution and in the form of nitrite salts. ... In chemistry, the standard state of a material is its state at 1 bar (100 kilopascals) and 25 degrees Celsius (298. ... A chemical compound is a chemical substance formed from two or more elements, with a fixed ratio determining the composition. ... A gas is one of the four main phases of matter (after solid and liquid, and followed by plasma), that subsequently appear as a solid material is subjected to increasingly higher temperatures. ...

Formation and occurrence

Nitric oxide (NO), also a common pollutant, oxidizes in air to the dioxide: The chemical compound nitric oxide is a gas with chemical formula NO. It is an important signaling molecule in the body of mammals including humans, one of the few gaseous signaling molecules known. ... Look up air in Wiktionary, the free dictionary. ...

2 NO + O₂ → 2 NO₂

NO₂ is generated by the action of nitric acid on a variety of metals, such as copper or silver. R-phrases , S-phrases , , , , Flash point not applicable RTECS number QU5775000 Supplementary data page Structure and properties n, εr, etc. ... General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic brown Atomic mass 63. ... General Name, Symbol, Number silver, Ag, 47 Chemical series transition metals Group, Period, Block 11, 5, d Appearance lustrous white metal Atomic mass 107. ...

2 HNO₃ + Ag → AgNO₃ + NO₂ + H₂O

"Red fuming nitric acid" owes its red color to the presence of NO₂.

Reactions

Nitrogen dioxide exists in equilibrium with its dimer, dinitrogen tetroxide. Nitrogen tetroxide (or dinitrogen tetroxide) (N2O4) is a hypergolic propellant often used in combination with a hydrazine-based rocket fuel. ...

2 NO₂ ↔ N₂O₄

The equilibrium favors NO₂ at higher temperatures. Solid NO₂ can be obtained as a solid from NO₂ by very rapid cooling (for example with liquid nitrogen), although it is commonly contains N₂O₄.

At −50 °C the crystals of N₂O₄ are colorless, but honey-yellow at the melting point. The vapour at −10 °C is pale yellow and deepens as the temperature rises up to a maximum at about 183 °C, at which point a 2 cm thick layer of the gas between glass is essentially black and opaque. The color of the gas is a good indicator of the concentration of NO₂, which below 183 °C increases with increasing temperature. Above 183 °C, NO₂ converts to NO and O₂.

NO₂ reacts with water, even at ambient temperatures and pressure, where it disproportionates to nitric and nitrous acid. That reaction is used in the Ostwald process, the industrial route to nitrate-based fertilizers and explosives. A girl in a swimming pool Water (from the Old English waeter; c. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... Pressure (symbol: p) is the force per unit area acting on a surface in a direction perpendicular to that surface. ... R-phrases , S-phrases , , , , Flash point not applicable RTECS number QU5775000 Supplementary data page Structure and properties n, εr, etc. ... Nitrous acid weak monobasic acid known only in solution and in the form of nitrite salts. ... The Ostwald process is chemical process for producing nitric acid, which was developed by Wilhelm Ostwald (patented 1902). ... A tractor at work Fertilizers or fertilisers are compounds given to plants with the intention of promoting growth; they are usually applied either via the soil, for uptake by plant roots, or by foliar spraying, for uptake through leaves. ... This article is concerned solely with chemical explosives. ...

Structure and bonding

NO₂ is a radical having a lone - or unpaired - electron, which renders this molecule paramagnetic and is involved in the electronic transitions that give rise to its color. The dimer, N₂O₄, is diamagnetic.

Safety and pollution considerations

Nitriogen dioxide is toxic by inhalation. Symptoms of poisoning (lung edema) tend to appear several hours after one has inhaled a low but potentially fatal dose. Also, low concentrations (4 ppm) will anesthesize the nose, thus creating a potential for overexposure. Pulmonary edema is swelling and/or fluid accumulation in the lungs. ...

Long-term exposure to NO₂ at concentrations above 40–100 µg/m³ causes adverse health effects [2]. The most important source of NO₂ are internal combustion engines, which emit nitrogen oxides near people.

This map, depicting results of satellite measurements, illustrates nitrogen dioxide as large scale pollutant, with rural background ground level concentrations in some areas around 30 µg/m³, not far below unhealthful levels. Nitrogen dioxide plays a role in atmospheric chemistry, including the formation of tropospheric ozone. Ozone (O3) is a key constituent of the troposphere. ...

NO₂ pollution levels in Europe.

A recent study by researchers at the University of California, San Diego, suggests a link between NO₂ levels and Sudden Infant Death Syndrome [3]. Download high resolution version (1811x1340, 1998 KB)Nitrogen dioxide pollution levels in Europe Credit: University of Heidelberg Original caption released with image NO2 levels over Europe A detail from a global image shows the European mean tropospheric nitrogen dioxide (NO2) vertical column density (VCD) between January 2003 and June 2004... Download high resolution version (1811x1340, 1998 KB)Nitrogen dioxide pollution levels in Europe Credit: University of Heidelberg Original caption released with image NO2 levels over Europe A detail from a global image shows the European mean tropospheric nitrogen dioxide (NO2) vertical column density (VCD) between January 2003 and June 2004... Europe is conventionally considered one of the seven continents of Earth which, in this case, is more a cultural and political distinction than a physiographic one, leading to some dispute as to Europes actual borders. ... The University of California, San Diego (popularly known as UCSD) is a public, coeducational university located in La Jolla, California. ...

See Also

• Nitrous oxide or N₂O, "laughing gas", a linear molecule, isoelectronic with CO₂ but with a nonsymmetric arrangement of atoms (NNO)
• Nitric oxide or NO, a problematic pollutant, related to CO but with one additional electron.
• Nitrogen dioxide, NO₂, also a serious pollutant, with a bent structure .
• NOx = all of the above in unspecified proportions but tending toward NO₂.

More esoteric nitrogen oxides include N₂O₅ and the blue species N₂O₃. Nitrous oxide, also known as dinitrogen oxide or dinitrogen monoxide, is a chemical compound with chemical formula N2O. Under room conditions, it is a colourless non-flammable gas, with a pleasant, slightly-sweet odor. ... Two or more molecular entities (atoms, molecules, ions) are described as isoelectronic if they have the same number of valence electrons and the same structure (number and connectivity of atoms), but may differ in the elements involved. ... Carbon dioxide is an atmospheric gas comprised of one carbon and two oxygen atoms. ... The chemical compound nitric oxide is a gas with chemical formula NO. It is an important signaling molecule in the body of mammals including humans, one of the few gaseous signaling molecules known. ... Carbon monoxide, chemical formula CO, is a colorless, odorless, tasteless, flammable and highly toxic gas. ... Dinitrogen pentoxide is the binary nitrogen oxide N2O5, also known as nitrogen pentoxide. ...

Oxidized (cationic) and reduced (anionic) derivatives of many of these oxides exist: nitrite or NO₂^-, nitrate or NO₃^-, nitronium or NO₂⁺, and nitrosonium or NO⁺. NO₂ is intermediate between nitrite and nitronium: // Definition The nitrite ion is NO2−. A nitrite compound is one that contains this group, either an ionic compound, or an analogous covalent one. ... In inorganic chemistry, a nitrate is a salt of nitric acid. ... The nitronium ion is NO2+, a nitrogen atom and two oxygen atoms with a positive charge. ... The structure of the nitrosonium ion The nitrosonium ion is NO+, the nitrogen atom is bonded to an oxygen atom with a bond order of 2, the overall diatomic species bearing a positive charge. ...

NO₂⁺ + e → NO₂

NO₂ + e → NO₂^-

External links

• International Chemical Safety Card 0930
• National Pollutant Inventory - Oxides of nitrogen fact sheet
• NIOSH Pocket Guide to Chemical Hazards
• WHO-Europe reports: Health Aspects of Air Pollution (2003) (PDF) and "Answer to follow-up questions from CAFE (2004) (PDF)
• Nitrogen dioxide pollution in the world (image)
• Nitrogen Dioxide Air Pollution — A summary for non specialists by GreenFacts of the above WHO reports.
• Computational Chemistry Wiki
• European Chemicals Bureau
• NIST Chemistry WebBook