Ionic nitrides

Ammonia is also produced when an ionic nitride is hydrolysed, for example magnesium nitride, produced when magnesium burns in nitrogen ... 

We distinguish three kinds of nitrides, i.e. ionic nitrides (e g. Th3N2), covalent nitrides (e.g. BN) and intermediate forms (e g. VN). These intermediate forms are extremely inert, very hard and they have high melting points. VN has a Mohs hardness of 9-10 and a melting point of 2570 °C. Furthermore, the intermediate form conducts electricity since the electronic band structure of the metal is maintained when N atoms are placed in the cavities of the crystal lattice... 

The reaction of an ionic nitride (e.g., Mg3N2) with water can also be used. 

As with carbides, there are three general classes. Ionic nitrides are formed by Li, Mg, Ca, Sr, Ba, Zn, and some others. Their formulas correspond to what would result from combination of the normal metal ions with N3- ions. They are all essentially ionic and are properly written as (Ca2+)3(N3 )2, (Li+)3N3, and so on. Nitrides of the type are often anti-isomorphous with oxides of the M203 type. This does not in itself mean that, like the oxides, they are ionic. However, their... 

The group 2 elements all bum in nitrogen and form ionic nitrides of the formula M3N2 (e.g. equation 15). Owing... 

The nitrides (see Nitrides Transition Metal Solid-state Chemistry) can be divided ronghly into ionic nitrides (e.g. alkali and alkaline-earth nitrides), covalent nitrides (e.g. 

The heavier alkaline earth metals react with nitrogen or hydrogen at high temperatures to produce ionic nitride or hydride salts. For example ... 

In contrast to ionic phosphides which upon protonolysis yield P2H4 along with PHj (see 1.5.3.2.1), ionic nitride protonolyses do not yield N H, except for BajN which, when heated with H O at 380°C, produces N H. ... 

Salt-like or ionic nitrides, in which N forms primarily ionic bonds to alkali metals, rare earth metals, and members of group IIIA. Although actinide nitrides are also included in this grouping, they may equally well be classified as metallic. Compounds in this group are readily hydrolyzed and must thus be protected from moisture. 

In contrast to the ionic nitrides of Zn or Cd, the chocolate-coloured explosive Hg3N2 made from Hgl2 and KNH2 in liquid ammonia, is presumably a covalent compound. For the nitrides of B, Al, Ga, In, and T1 the geometrical possibilities are the same as for carbon, there being an average of 4 valence electrons per atom in MN. 

Most of the elements reduce nitrogen to form ionic nitrides ... 

Electron gain to form the nitride ion, N3-. This ion occurs only in the salt-like nitrides of the most electropositive elements, for example, Li3N. Many non-ionic nitrides exist and are discussed later in this Chapter. 

Hydrolysis of an ionic nitride is a convenient way of preparing ND3 (or Mg3N2 + 6D20 -> 3Mg(OD)2 + 2NDj... 

Only a few nominally ionic nitride perovskites are known, of which the best characterised is ThTaNj. This has the ideal cubic stmcture ... 

Metal nitrides are generally prepared by the direct reaction of the elements. Ionic nitrides are also prepared by the decomposition of metal amides as illustrated by the following reaction ... 

Ionic nitrides with N " as in LijN, AIN, and MgjNjl Covalent nitrides as BN and PjNji Interstitial nitrides as TiN and VN... 

Because the nitride ion,, is a very strong base, ionic nitrides react with water, producing ammonia. 

The nitrides and ammonia (including the ammonium salts) are the two major types of compounds in which nitrogen has a —3 oxidation state. The nitrides can be divided into ionic, covalent, and interstitial types in the same way as we saw earlier for the hydrides, oxides, and carbides. There are only a few ionic nitrides, the most important being those of lithium, the alkaline-earth metals, and zinc. These are prepared by direct reaction of the elements and readily hydrolyze to ammonia. 

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