Average mass of an atom in unified atomic mass units (1 u is 1/12 of the mass of a carbon-12 atom). Accounts for the natural mix of the element’s isotopes.
Number of the vertical column, 1 to 18 in IUPAC numbering. Elements in a group share the same outer-shell layout, so their properties are alike.
Number of the horizontal row. Usually equal to the number of electron shells in the atom; palladium is the exception, with four shells in period 5.
The subshell (s, p, d or f) that receives the last electrons in the usual filling order; it divides the table into four blocks. Real atoms sometimes differ: lanthanum starts the f-block but has no f electrons.
[He] 2s² 2p³
How electrons are arranged in subshells. The bracket stands for the previous noble gas; the superscript is the number of electrons in a subshell.
2, 5
Number of electrons in each shell, from the nucleus outwards.
-210 °C (63.15 K)
Temperature at which the solid turns liquid at standard pressure. Helium, carbon and arsenic do not melt at normal pressure: helium needs about 25 atm, carbon and arsenic turn straight into vapour.
-195.8 °C (77.36 K)
Temperature at which the liquid boils at standard pressure. For carbon and arsenic, the temperature at which the solid turns straight into vapour (sublimation).
0.001251 g/cm³
Mass of one cubic centimetre of the substance. For gases, at 0 °C and standard pressure.
3.04 Pauling
How strongly an atom pulls electrons towards itself in a chemical bond. On the Pauling scale it runs from 0.79 for caesium to 3.98 for fluorine.
14.534 eV
Energy needed to remove the most loosely bound electron from an atom. The lower it is, the more easily the element gives up an electron, which is typical of metals.
no stable negative ion
Energy released when a neutral atom gains an electron. Highest for the halogens. Noble gases, nitrogen and some metals form no stable negative ion.
71 pm
Half the length of a single covalent bond between two atoms of the element. It shows the size of an atom inside a molecule or crystal: 76 pm for carbon, 132 pm for iron.
+5, +4, +3, +2, +1, -1, -2, -3
Charges the atom would have in its compounds if all its bonds were ionic; the main ones are listed.
Nitrogen (N) is a chemical element with atomic number 7. It sits in group 15 and period 2 of the periodic table, in the p-block. It is a nonmetal. At room temperature it is a gas. Its standard atomic weight is 14.007.
Origin of the name
The English nitrogen comes from the French nitrogène, proposed by Jean-Antoine Chaptal: Greek nítron ‘saltpetre’ and -genēs ‘forming’, because the element is part of saltpetre. Antoine Lavoisier called it azote, ‘lifeless’, and French still does; German Stickstoff means ‘suffocating substance’.
Where is nitrogen found?
Nitrogen gas makes up 78% of the air by volume, yet the Earth’s crust holds little of it; its only notable minerals are saltpetres. Every living thing contains nitrogen in its proteins and DNA. Plants cannot take it from the air: soil bacteria “fix” it into compounds the plants can use. Industry separates nitrogen from liquefied air.
What is nitrogen used for?
Most nitrogen is combined with hydrogen into ammonia by the Haber process, and ammonia becomes fertilisers, explosives and nitric acid. Being unreactive, nitrogen gas protects goods from oxygen in electronics factories, in welding and in food packaging. Liquid nitrogen cools things quickly and keeps biological samples frozen.
Interesting facts
In 1772 Daniel Rutherford noticed that in the air left after removing oxygen a flame went out and an animal could not live.
Pure nitrogen suffocates without warning: a person breathing it feels no lack of air before passing out.
Aqua regia, a mixture of nitric and hydrochloric acids, dissolves gold, the “king of metals”, which is how it got its name.