Krypton (Kr)

Colorless gas

Krypton is a noble gas used in high-performance flash photography and energy-efficient windows, and with a filled 4p⁶ shell, krypton is chemically inert but can form KrF₂ under extreme conditions. The meter was once defined by the orange-red spectral line of krypton-86.

Key metrics

Density0.00375g/cm³

Melting point116K

Boiling point120K

Electronegativity3Pauling

Discovery

1898discovered

Discovered by: William Ramsay
Reactivity profile: Inert gas
Reactivity: Low
Bonding: Covalent

Electron configuration

\textcolor{#6b7280}{[Ar]}\; \textcolor{#22c55e}{3_{d}^{10}}\; \textcolor{#ef4444}{4_{s}^{2}}\; \textcolor{#3b82f6}{4_{p}^{6}}

[Ar] 3d10 4s2 4p6

Wave function

\Psi_{\text{Kr}} \approx \frac{1}{\sqrt{36!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{36}(\mathbf{r}_{36}) \right|

Probability density $|\Psi|^2$ across the Kr 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: 88 pm
Ionization energy: 1351 kJ/mol
Electron affinity: 0 kJ/mol
Crystal structure: Face-centered cubic (fcc)

Oxidation states

0+2

Acid/base

Neutral

Strongly acidicStrongly basic

State at 25 °CGas

116 K120 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

557.0nmKr I (green)Green70%

587.1nmKr I (yellow)Yellow100%

760.1nmKr I (red)IR50%

Dominant line 587.1 nmRange 557–760 nmTransitions 3