Nitrogen (7)

Nitrogen is a Group 15 element. Nitrogen makes up about 78% of the atmosphere by volume but the atmosphere of Mars contains less than 3% nitrogen. The element seemed so inert that Lavoisier named it azote, meaning "without life". However, its compounds are vital components of foods, fertilizers, and explosives. Nitrogen gas is colorless, odorless, and generally inert. As a liquid it is also colorless and odorless.

When nitrogen is heated, it combines directly with magnesium, lithium, or calcium. When mixed with oxygen and subjected to electric sparks, it forms nitric oxide (NO) and then the dioxide (NO2). When heated under pressure with hydrogen in the presence of a suitable catalyst , ammonia forms (Haber process). Nitrogen is "fixed" from the atmosphere by bacteria in the roots of certain plants such as clover, hence the usefulness of clover in crop rotation.

•Name: Nitrogen
•Symbol: N
•Atomic number: 7
•Atomic weight: 14.0067
•Standard state: gas at 298 K
•CAS Registry ID: 7727-37-9
•Group in periodic table: 15
•Group name: Pnictogen
•Period in periodic table: 2
•Block in periodic table: p-block
•Color: colorless
•Classification: Non-metallic

Historical information

Nitrogen was discovered by Daniel Rutherford at 1772 in Scotland. Origin of name: from the Greek words "nitron genes" meaning "nitre" and "forming" and the Latin word "nitrum" (nitre is a common name for potassium nitrate, KNO3).It was known during the 18th century that air contains at least two gases, one of which supports combustion and life, and the other of which does not. Nitrogen was discovered by Daniel Rutherford in 1772, who called it noxious air, but Scheele, Cavendish, Priestley, and others at about the same time studied "burnt" or "dephlogisticated" air, as air without oxygen was then called.

Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for nitrogen is a circle with a vertical line through the center.

Physical properties

•Melting point: 63.05 [or -210.1 °C (-346.18 °F)] K
•Boiling point: 77.36 [or -195.79 °C (-320.42 °F)] K
•Density of solid: 1026 kg m-3

Orbital properties

•Ground state electron configuration: [He].2s2.2p3
•Shell structure: 2.5
•Term symbol: 4S3/2

Isolation

There is never any need to make nitrogen in the laboratory as it is readily available commercially or through in-house air liquefaction plants. However the decomposition of sodium azide is one route to N2 and decomposition is ammonium dichromate is another. Both reactions must only be carried out under controlled conditions by a professional.

NaN3 (300°C) → 2Na + 3N2

(NH4)2Cr2O7 → N2 + Cr2O3 + 4H2O

Nitrogen is made on massive scale by liquefaction of air and fractional distillation of the resulting liquid air to separate out oxygen and other gases. Very high purity nitrogen is available by this route.