ABOUT HELIUM

 HELIUM

Symbol --- He

Abundance --- in the universe (23%), in the earth crust (5.5 x 10^-7%)

Physical state --- gas

Elemental Category --- noble gas

Colour --- colourless

Discovery --- Pierre Janssen, Norman Lockyer (1868)

Atomic no --- 2

Atomic weight --- 4.0026

Period --- 1

Group --- 18

Block --- s-block

Known Isotopes--- ₂He² ₂He³ ₂He⁴ ₂He⁵ ₂He⁶ ₂He⁷ ₂He⁸ ₂He⁹ ₂He¹⁰   

Stable Isotopes --- ₂He³ ₂He⁴

Isotopic abundance ---

[₂He³(0.0002%),₂He⁴(99.9998%)]

Melting Point --- 0.95 K or -272.20 ⁰C

Boiling Point --- 4.22 K or -268.93 ⁰C

Density (at STP) --- 0.1786 g/L

Electron Configuration --- 1s²

Oxidation States --- 0

Valence --- 0

Ionisation Energy --- 2372.3 KJ/mol (1st), 

5250.5 KJ/mol (2 nd)

Covalent Radius --- 28 pm

Van der Waals radius --- 140 pm

Crystal Structure --- Hexagonal closed packed (hcp)

Heat of fusion --- 0.0138 KJ/mol

Heat of vaporisation --- 0.0829 KJ/mol

Triple Point --- 2.177 K, 5.043 KPa

Critical Point --- 5.195 K, 0.227 MPa (2.24 atm)

Molar heat capacity --- 20.78 J/mol-K

Specific heat --- 5193.1 J/(Kg-K)

Thermal conductivity --- 0.1513 W/(m k)

Adiabatic index --- 5/3

Molar volume --- 0.022424

Refractive index --- 1.000035

Speed of sound --- 972 m/s

Magnetic type --- diamagnetic

Mass magnetic susceptibility ---  - 5.9 x10^-9 m³/kg

Molar magnetic susceptibility --- - 2.36 x10^-11 m³/mol 

Lattice angles --- π/2, π/2, π/2

Lattice constants --- 424.2 pm,424.2 pm,424.2 pm 

Quantum numbers --- ¹S₀

Neutron cross section --- 0.007

Neutron mass absorption --- 0.00001

About Helium