HELIUM, He (2)

Helium is a monoatomic, colourless and inert gas and is the second lightest chemical element with the lowest boiling and melting points.

ELEMENT BRIEF

1868, Pierre Janssen and Norman Lockyer

DISCOVERY

Ancient Greek, hḗlios, the sun.

ETYMOLOGY

Helium

ELEMENT

He

SYMBOL

2

ATOMIC NUMBER

7440-59-7

CAS NUMBER

ELEMENTAL SPECTRUM

Colourless

ELEMENTAL COLOUR

1.000'035

REFRACTIVE INDEX

-

POISSON RATIO

22.424 cm³

MOLAR VOLUME

-

BRINELL HARDNESS

-

MOHS HARDNESS

-

VICKERS HARDNESS

970 m/s, Mach 2.828'0

SPEED OF SOUND

-

BULK MODULUS

-

SHEAR MODULUS

-

YOUNG MODULUS

ALLOTROPES

0.95 K, -272.20 °C

MELTING POINT

4.22 K, -268.93 °C

BOILING POINT

-

AUTOMATIC IGNITION

-

FLASHPOINT

5.19 K, -267.96 °C

CRITICAL TEMPERATURE

227.00k Pa, 2 Atm

CRITICAL PRESSURE

0.151'300 W/(m K)

THERMAL CONDUCTIVITY

-

THERMAL EXPANSION

5,193.10 J/(kg K)

SPECIFIC HEAT

0.020 kJ/mol

HEAT FUSION

0.083 kJ/mol

HEAT VAPORISATION

-

HEAT COMBUSTION

-

CURIE POINT

-

NEEL POINT

5/3

ADIABATIC INDEX

Gas

PHASE

-

ELECTRICAL TYPE

-

CONDUCTIVITY

-

RESISTIVITY

-

SUPERCONDUCTING POINT

Diamagnetic

MAGNETIC TYPE

-0.000'000'005'9

MASS SUSCEPTIBILITY

-0.000'000'000'023'60

MOLAR SUSCEPTIBILITY

-0.000'000'001'05

VOLUME SUSCEPTIBILITY

Noble Gas

CLASSIFICATION

4.002'601'9

ATOMIC WEIGHT

31 pm

ATOMIC RADIUS

46 pm

COVALENT RADIUS SINGLE BOND

-

COVALENT RADIUS DOUBLE BOND

-

COVALENT RADIUS TRIPLE BOND

140 pm

VAN DER WAALS RADIUS

1s²

ELECTRON CONFIGURATION

Hexagonal, Close Packed Single

CRYSTAL STRUCTURE

-

DENSITY AS SOLID

-

DENSITY AS LIQUID

0.178'50 g/cm³

DENSITY AS GAS

Fm_3m

SPACE GROUP NAME

225

SPACE GROUP NUMBER

π/2, π/2 & π/2

LATTICE ANGLES

424.2, 424.2 & 424.2 pm

LATTICE CONSTANTS

0

VALENCE

-

ELECTRONEGATIVITY

-48.24 kJ/mol

ELECTRON AFFINITY

IONISATION ENERGY