Neon at a glance
- Atomic number
- 10
- Symbol
- Ne
- Atomic mass
- 20.18 u
- Category
- Noble gas
- Group / period
- 18 / 2
- Electron configuration
- [He] 2s 2 2p 6
- State at 25 °C
- Gas
- Melting point
- -248.6 °C
- Boiling point
- -246.1 °C
- Density
- 0.9 g/L
- Electronegativity
- n/a
- 1st ionization energy
- 2081 kJ/mol
- Oxidation states
- 0
- Discovered
- 1898
Atomic structure
A neutral neon atom has 10 protons and 10 electrons, and its most common isotope carries about 10 neutrons. One atom weighs about 3.35 × 10⁻²⁶ kg, so a mole of neon (6.022 × 10²³ atoms) weighs 20.18 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 8), which gives the configuration [He] 2s 2 2p 6. Its outer shell is full, which is why neon hardly reacts with anything. It has 3 stable isotopes: Ne-20, Ne-21 and Ne-22. No other element has a stable isotope with mass number 20, so Ne-20 has no stable isobars; its neighbours on that line decay into it or away from it.
Physical properties
At room temperature (25 °C) neon is a gas. It melts at -248.6 °C and boils at -246.1 °C, so it stays liquid across a 2.51-degree range. To turn liquid it has to be cooled below -246.1 °C, colder than liquid nitrogen (−196 °C). Only 2 elements have a lower melting point. As a gas it weighs 0.9 g per litre, 1.3 times lighter than air. Its atoms have a radius of about 38 pm (Fluorine next door is 50 pm). In the solid, its atoms pack into a face-centred cubic lattice.
Chemical behaviour
It has no measured electronegativity, because it almost never forms bonds. Pulling off its outermost electron takes 2081 kJ/mol, less than Helium above it (2372 kJ/mol). It usually keeps an oxidation state of 0. Group 18 also holds Helium, Argon, Krypton, Xenon, Radon and Oganesson, which share its outer-shell pattern. Its Lewis symbol is Ne surrounded by 8 dots. Handle with care: as a pure element it is asphyxiant gas.
Where it comes from
It makes up 0.005 mg/kg of Earth's crust, the 73rd most abundant element there. It was first identified in 1898, making it the 77th 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 640.2 nm, 585.2 nm and 614.3 nm.