NITROGEN AND ITS COMPOUNDS

NITROGEN AND ITS COMPOUNDS

The Nitrogen family are known as PNICOGENS and their compound as PNICOMIDES. The name is derived from the Greek word PNICOMIGS meaning suffocation.

The Nitrogen family are group 15 (VA) which contains Nitrogen, Phosphorous, Arsenic, Antimony and Bismuth. Elements in group VA have five valence electrons. Because the elements can either gain three electrons or lose five to gain a stable configuration.

Element/symbol	Atomic No	Mass No	Electronic configuration	Common physical form
Nitrogen [N]	7	14.01	1s22s22P3	Colourless gas
Phosphorous[P]	15	30.97	[Ne]3s23P3	White solid/Red solid
Arsenic[As]	33	74.92	[Ar]3d104s24P3	Yellow solid/Grey solid
Antimony[Sb)	51	121.76	[Kr]4d105s25P3	Yellow solid/silver-white metallic solid
Bismuth [Bi]	83	208.98	[Xe]4f145d106s26p3	Pink-white metallic solid

GENERAL PROPERTIES OF NITROGEN FAMILY

1.       As you move down the Nitrogen family: atomic radius increases, ionic radius increases, ionization energy decreases and electronegativity decreases; melting point and boiling point increases; metallic character increases.

2.       They often form covalent compounds, usually with the oxidation number of +3 or +5.

3.       Nitrogen and Phosphorous are non-metals, Arsenic and Antimony are metalloids. Bismuth is a metal.

4.       Except for nitrogen, the elements are solid at room temperature.

5.       Except for nitrogen and bismuth, the elements exist in two or more allotropic form.

LABORATORY PREPARATION OF NITROGEN

Nitrogen is prepared by the following chemical methods:

1.       From the atmosphere: Since nitrogen makes up a large percentage of air, it can be obtained from air by removing the other constituent. Carbon (IV) oxide is removed by passing the air through caustic soda. 2NaOHaq + CO2g                   Na2CO3aq +  H2Ol

Oxygen is removed with heated copper turning

2Cus + O2g      2CuOs

The nitrogen obtained through this method is found to have a slightly higher density than pure nitrogen because of the presence of about 1% by volume of rare gases as impurities.

2.       Thermal decomposition of ammonium dioxonitrate (III): Pure nitrogen is obtained by the thermal decomposition of ammonium dioxonitrate (III) is unstable and decomposes exothermically. Hence, it is not heated directly. However a mixture of sodium dioxonitrate (III) and ammonium chloride solutions is a ratio of 7:5 is heated to produce ammonium dioxonitrate which in turn decomposes to yield nitrogen and steam.

NaNO2aq   +  NH4Claq                            NH4NO2  +  NaClaq

NH4NO2aq          N2g  +  2H2Ol

3.        From ammonium heptaoxodichromate(VI): It decomposes on heating to yield nitrogen.

(NH4)2Cr2O7s                         N2g  + Cr2O3s +  4H2O

4.       Oxidation of ammonia gas by copper(II) oxide: Nitrogen is liberated when ammonia is passed over hot copper (II) oxide.

2NH3g + 3CuOs                  3Cus +  3H2Og + H2g

5.       Reduction of oxides of nitrogen by heated copper: When dinitrogen (I) oxide is passed over red-hot copper, the gas is reduced to nitrogen.

NO2s + Cus                  CuOs + N2g

INDUSTRIAL PREPARATION OF NITROGEN

Industrially, nitrogen is prepared by the fractional distillation of liquid air. Air, from which carbon (IV) oxide has been removed, is liquified by subjecting it to successive compression and cooling processes. Upon distillation, nitrogen gas is evolved first at -196oC (at S.p) and is separate from oxygen which boils at -183oC (at S.p). Nitrogen is stored in steel cylinders and sold as liquid nitrogen or as the compressed gas.

PHYSICAL PROPERTIES OF NITROGEN

1.       Nitrogen is a colourless, odourless, and tasteless gas.

2.       Pure nitrogen is slightly lighter than air.

3.       It is only slightly soluble in water. Two volumes of the gas dissolve in 100 volume of water at room temperature.

4.       It has a melting point of -210oC and a boiling point of -196oC.

5.       It exhibit oxidation states varying from -3 to +5 in its various compound.

CHEMICAL PROPERTIES OF NITROGEN

Free nitrogen exists in air as a diatomic molecule with triple covalent bonds between its atoms (:N-N:). The high bond energy of triple bond makes the bond very stable and accounts for the unreactive nature of nitrogen under ordinary condition. However, at very high temperature and pressure, nitrogen combine directly with certain metals and non-metals.

1.       With metals: Red-hot magnesium combines directly with nitrogen to produce magnesium nitrides.

3Mgs + N2g                  Mg3N2s

The nitride hydrolysed readily when warmed with water to give ammonia gas.

Mg3N2s + 6H2Ol                               3Mg(OH)2g + NH3g

2.       With non-metal: Nitrogen combines with hydrogen to produce ammonia.

N2g  +  3H2g              2NH3g

It also combine with oxygen at very high temperature to form nitrogen (II) oxide. This action occurs in nature in the atmosphere when lighting  flashes.

N2g  + O2g                2NOg

USES OF NITROGEN

1.       It is used in the manufacture of ammonia, cyanide, fertilizer and production of nitric acid.

2.       Liquid nitrogen is used as cooling agent.

3.       Nitrogen is also used to protect historical document such as declaration of independence.

4.       Liquid nitrogen is used by the oil industry to build up pressure in well to force crude oil upward.

5.       Nitrogen is used due to inert nature as a carrier gas in gas chromatography and as a preservative to prevent rancidity in packaged foods.