Nitrogen at a glance
- Atomic number
- 7
- Symbol
- N
- Atomic mass
- 14.007 u
- Category
- Reactive nonmetal
- Group / period
- 15 / 2
- Electron configuration
- [He] 2s 2 2p 3
- State at 25 °C
- Gas
- Melting point
- -210 °C
- Boiling point
- -195.8 °C
- Density
- 1.25 g/L
- Electronegativity
- 3.04
- 1st ionization energy
- 1402 kJ/mol
- Oxidation states
- −3, +3, +5
- Discovered
- 1772
Atomic structure
A neutral nitrogen atom has 7 protons and 7 electrons, and its most common isotope carries about 7 neutrons. One atom weighs about 2.33 × 10⁻²⁶ kg, so a mole of nitrogen (6.022 × 10²³ atoms) weighs 14.007 g. That nucleus holds 1 neutrons for every proton, close to the one-to-one balance that light nuclei prefer. The electrons fill 2 shells (K 2, L 5), which gives the configuration [He] 2s 2 2p 3. With 5 electrons in its outer shell, it tends to gain or share electrons to complete its outer shell. It has 2 stable isotopes: N-14 and N-15. No other element has a stable isotope with mass number 14, so N-14 has no stable isobars; its neighbours on that line decay into it or away from it.
Physical properties
At room temperature (25 °C) nitrogen is a gas. It melts at -210 °C and boils at -195.8 °C, so it stays liquid across a 14.21-degree range. To turn liquid it has to be cooled below -195.8 °C, colder than dry ice (−78 °C). Only 5 elements have a lower melting point. As a gas it weighs 1.25 g per litre, 1 times heavier than air. Its atoms have a radius of about 65 pm (Carbon next door is 70 pm). In the solid, its atoms pack into a hexagonal close-packed lattice.
Chemical behaviour
Its electronegativity is 3.04 on the Pauling scale, the 4th highest of all elements, so it pulls hard on shared electrons. Pulling off its outermost electron takes 1402 kJ/mol. A bond between nitrogen and chlorine would be almost non-polar covalent, with an electronegativity difference of 0.12. Its common oxidation states are −3, +3, +5, so in compounds you will usually meet it as N³⁻, N³⁺ and N⁵⁺. Group 15 also holds Phosphorus, Arsenic, Antimony, Bismuth and Moscovium, which share its outer-shell pattern. Its Lewis symbol is N surrounded by 5 dots. Handle with care: as a pure element it is asphyxiant gas.
Where it comes from
It makes up 19 mg/kg of Earth's crust, the 34th most abundant element there. In the human body it accounts for about 3.2 % of body mass, making it one of the main building blocks of life. It was first identified in 1772, making it the 20th element to be discovered (counting the 11 known since antiquity together). When excited it glows at its own set of colours; its brightest visible lines are at 500.5 nm, 567.6 nm and 575.3 nm.