Argon (Ar)

Colorless gas

Argon is the third most abundant gas in Earth's atmosphere, making up nearly 1% of the air we breathe, and with a completely filled 3p⁶ shell, argon is chemically inert and is used as a protective shielding gas in welding and 3D printing to prevent oxidation of molten metals.

Key metrics

Density0.001784g/cm³

Melting point83.8K

Boiling point87.3K

Electronegativity0Pauling

Discovery

1894discovered

Discovered by: Lord Rayleigh
Reactivity profile: Inert
Reactivity: Low
Bonding: Covalent

Electron configuration

\textcolor{#6b7280}{[Ne]}\; \textcolor{#ef4444}{3_{s}^{2}}\; \textcolor{#3b82f6}{3_{p}^{6}}

[Ne] 3s2 3p6

Wave function

\Psi_{\text{Ar}} \approx \frac{1}{\sqrt{18!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{18}(\mathbf{r}_{18}) \right|

Probability density $|\Psi|^2$ across the Ar valence shell.

Crystal structure

Face-Centered Cubic

Lattice constantsa = 1.00

Cell anglesα = β = γ = 90°

Coordination number12

Atoms per cell4

Atomic packing factor0.74

Physical properties

Atomic radius: 71 pm
Ionization energy: 1521 kJ/mol
Electron affinity: 0 kJ/mol
Crystal structure: Face-centered cubic (fcc)

Oxidation states

Acid/base

Neutral

Strongly acidicStrongly basic

State at 25 °CGas

83.8 K87.3 K298 K

Emission spectrum

4 transitions

380450500550600650700780

VioletBlueGreenYellowRed

696.5nmAr IRed60%

706.7nmAr IIR80%

750.4nmAr I (red)IR100%

811.5nmAr I (IR)IR70%

Dominant line 750.4 nmRange 697–812 nmTransitions 4