Nitrogen
Nitrogen is a chemical element with symbol N and atomic number 7. It is the lightest pnictogen and at room temperature, it is a transparent, odorless diatomic gas. Nitrogen is a common element in the universe, estimated at about seventh in total abundance in the Milky Way and the Solar System.
At a glance
- Atomic number
- 7
- Atomic mass
- 14.007 u
- Phase
- Gas
- Density
- 1.251 g/L
- Melting point
- 63.15 K
- Boiling point
- 77.355 K
- First ionization energy
- 1,402.3 kJ/mol
- Electronegativity
- 3.04
- Electron affinity
- -6.8 kJ/mol
- Molar heat capacity
- Unavailable
- Period
- 2
- Appearance
- colorless gas, liquid or solid
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Nitrogen’s orbitals use a hydrogen-like approximation. Every orbital of each visible subshell is shown: in Shapes as the surface holding half its probability, with light and dark shades for opposite signs of the wavefunction; in Cloud as dots where its electrons are likely to be. Sizes are stepped by shell, like the Shell model.
Preparing the orbital view…
7 protons7 neutrons
Nitrogen-14: its most common form in nature, or its longest-lived if it has none. The nucleus is drawn far too big: it’s about 100,000 times smaller than the atom.
Turn up the heat
A step of 1 K is the same size as 1 °C, so the two scales are always 273.15 apart. Fahrenheit is different: its degrees are smaller and it starts elsewhere, so water freezes at 273.15 K, 0 °C and 32 °F.25 °C · 77 °FGas
At this temperature, nitrogen is a gas.
At normal atmospheric pressure (1 atm). The temperature scale is logarithmic. The particle box is schematic: real samples hold vastly more atoms, and spacing and speeds are not to scale.
Pull the electrons off
NNeutral atom · no charge
A neutral nitrogen atom. Removing its first electron takes 1,402 kJ/mol.
Nitrogen’s outer shell holds 5 electrons. Electron 6 is the first from an inner shell: it sits closer to the nucleus with less shielding, so removing it takes 5.6× as much energy as the one before.
What does this tell us?
- The jumps let you count electrons. Between the dashed lines there are 5, then 2 bars. Read backwards, that’s 2, 5: the same electrons per shell as the shell model above. Jumps like these are part of the evidence that shells exist.
- The 5 electrons before the first big jump are nitrogen’s valence electrons, the ones it uses in chemical reactions. That’s why nitrogen sits in group 15: every element in the group has the same number of outer electrons, so they react in similar ways.
- Removing electrons from nitrogen is expensive from the start (1,402 kJ/mol for the first). So in reactions nitrogen tends to gain or share electrons rather than lose them.
- Within a shell the steps rise gently. Each electron removed leaves fewer electrons pushing the others away, while the nucleus pulls just as hard, so the next one is held a little more tightly.
Show the values as a table
| Electron | Shell | Energy (kJ/mol) | × previous | Value |
|---|---|---|---|---|
| 1 | 2 | 1,402 | – | Measured |
| 2 | 2 | 2,856 | 2 | Estimated |
| 3 | 2 | 4,578 | 1.6 | Estimated |
| 4 | 2 | 7,475 | 1.6 | Measured |
| 5 | 2 | 9,445 | 1.3 | Measured |
| 6 | 1 | 53,266 | 5.6 | Calculated |
| 7 | 1 | 64,360 | 1.2 | Calculated |
Successive ionization energies of gas-phase atoms and ions from the NIST Atomic Spectra Database. Solid bars are measured; hatched bars were estimated from nearby measurements or calculated from quantum theory, as is usual for highly charged ions. Electrons are taken from the outermost shell first, a simplification: electrons in different subshells of the same shell also differ in energy. On the log scale each gridline is 10 times the one below.
Try to break the triple bond
Nitrogen makes up 78% of the air, yet it hardly reacts with anything. Its two atoms share three pairs of electrons: a triple bond, one of the strongest in chemistry. Pour energy into three molecules and see which bond gives way first.
- F₂ FluorineSingle bond, 141.2 pm long0% of the way
- O₂ OxygenDouble bond, 120.7 pm long0% of the way
- N₂ NitrogenTriple bond, 109.8 pm long0% of the way
Drag the slider to pour energy in.
More shared pairs of electrons pull the atoms closer and hold them tighter: a triple bond is shorter and much stronger than a single one.
Why it matters: breaking nitrogen
Every living thing needs nitrogen to build proteins and DNA, and the air is full of it. But while it’s locked in N≡N, plants can’t use it. Something has to break that triple bond first.
- Lightning
A lightning bolt heats the air so much that nitrogen and oxygen combine. Rain washes the result into the soil.
- Bacteria
Bacteria in the roots of peas, beans and clover carry an enzyme that breaks N≡N at everyday temperatures, turning it into ammonia the plant can use.
- The Haber process
Since 1913, factories have forced nitrogen and hydrogen together over an iron catalyst at about 450 °C and 200 times air pressure, making ammonia for fertiliser. Roughly half of the world’s food now depends on it.
Bond energies at 25 °C (CRC Handbook of Chemistry and Physics); bond lengths from NIST. Energies are per mole of molecules: 945 kJ breaks every N≡N bond in 28 grams of nitrogen. The share of food that depends on the Haber process is from Erisman and colleagues, Nature Geoscience (2008).
How does it compare?
Density
0.00125 g/cm³4th lowest of 99
Melting point
63.2 K5th lowest of 96
Boiling point
77.4 K4th lowest of 97
Electronegativity
3.044th highest of 96
First ionization energy
1,402 kJ/mol5th highest of 99
Elements 1–99 from the reference data; heavier elements are left out because only a few atoms have ever been made, so their bulk properties are predictions. First ionization energies come from NIST. Density uses a logarithmic scale, because gases are around a thousand times less dense than solids; gas densities are at 0 °C and 1 atm. Melting and boiling points are at normal pressure. Everyday temperatures and light sources in the pictures are approximate. Hover over a dot to see the element, or click it to compare.
Keep exploring
Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.
- NitrogenRoyal Society of Chemistry
- NitrogenWikipedia
- Quantum numbers and electron configurationsPurdue
- Hydrogenic wavefunctionsNIST
- Ionization energiesNIST Atomic Spectra Database