Periodex

General properties

Group

group 18 (noble gases)

Period

period 4

Category

noble gases

Standard atomic weight

83.798(2)

Melting point

115.78 K (-157.37 °C)

Boiling point

119.93 K (-153.22 °C)

Phase at STP

gas

Additional properties

Block

p-block

Electron configuration

[Ar] 3d¹⁰ 4s² 4p⁶

Electrons per shell

2, 8, 18, 8

Electronegativity

3.00

Density

3.749 g/L

Oxidation states

0, +1, +2

CAS Number

7439-90-9

Natural isotopes

Discovery history

Discovered by

William Ramsay and Morris Travers

Year of discovery

1898

Origin of name

The Greek 'kryptos', meaning hidden