Mendeleev's Periodic Table > He - Helium

He - Helium

Helium is a light inert gas and the second most abundant element in the universe. Helium was discovered in 1868 by J. Norman Lockyear in the spectrum of a solar eclipse. Elemental helium is a colourless odourless monoatomic gas. Helium is the second most abundant element in the universe after hydrogen.

Atomic number - 2 Density g/mL 0 .0001787
Atomic weight u 4 .0026 Melting point K 0 .95
Bonding radius A 0 .93 Boiling point K 4 .215
Atomic radius A 0 .49 Heat of vaporization kJ/mol 0 .0845
Ionization Potential V 24 .587 Heat of fusion kJ/mol -
Electronegativity - - Specific heat J/gK 5 .193
The oxide is unknown. Crystal are hexagonal.
Electron config. : 1s2

Isotopes of He (Helium):

MASS abundancy
Halflife
Particle, Energy
Decay Product(s)
Isotopic Mass		 003 0.000137%

Stable

3.0160293 		004 99.999863%

Stable

4.0026032 		005
0.60 MeV
a/n,2.980 MeV
n/He-4
5.0122276 		006
806.7 msec
B-,3.508 MeV
Li-6
6.0188880
MASS abundancy
Halflife
Particle, Energy
Decay Product(s)
Isotopic Mass		 007
160KEV
n,1.372 MeV
He-6
7.0280302 		008
119.0 msec
B-/B-n,10.653
Li-8/Li-7
8.0339218 		009
0.3 MeV
n,1.150 MeV
He-8
9.0438220 		010
0.3 MeV
n,16.775 MeV
He-9
10.052399


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