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In chemistry a nitride is a compound of nitrogen with a less electronegative element where nitrogen has an oxidation state of -3. Note that there are exceptions to this naming convention, the nitrides of hydrogen, NH3 and carbon, (CN)2, are called ammonia and cyanogen respectively and that the nitrides of bromine, iodine are called nitrogen tribromide and nitrogen triiodide. Note that nitrogen also forms pernitrides, that contain N22− and azides, that contain N3−.
Classification of such a varied group of compounds is necessarily arbitrary. The following is based around their structure:
Additional recommended knowledge
The nitride ion is N3− (a nitrogen atom plus three electrons). The extra electrons give the nitrogen atom a closed inert gas shell. The nitride ion is isoelectronic with the oxide anion, O2−, and the fluoride anion, F− and has an ionic radius estimated to be 140 pm. The nitride ion is a strong π-donor ligand, stronger than O2−. It forms nitrido complexes which have a short metal nitrogen bond length indicating multiple bonding.
Salt like nitrides
The salt like nitrides are formed by:
Lithium nitride and the alkaline earth nitrides deprotonate hydrogen gas, and are rapidly hydrolysed by water to form ammonia.
The interstitial nitrides are formed by transition metals where there is a sufficient difference in size between the metal atom and the nitrogen to allow the host metal lattice to accommodate the nitrogen atom. This condition is true for the group 4, 5 and 6 transition metals i.e. the Titanium, Vanadium and Chromium groups. The group 4 and 5 nitrides are refractory i.e. high melting and chemically stable.
Group 7 and 8 transition metals form nitrides that decompose readily e.g iron nitride, Fe2N melts with decomposition at 200oC. The precious metals are currently being investigated by a number of researchers and thin films of platinum, gold and osmium nitrides have been produced. However there is some discussion as to their structures and their properties. Platinum nitride and osmium nitride for example are now believed to contain N2 units and as such should not be called nitrides.  
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Nitride". A list of authors is available in Wikipedia.|