Helium (He)

Helium is the 2nd element in the periodic table and has a symbol of He and atomic number of 2. It has an atomic weight of 4.00260 and a mass number of 4. Helium has two protons and two neutrons in its nucleus, and two electrons in one shell. It is located in group eighteen, period one and block s of the periodic table. Colourless, odourless gaseous nonmetallic element. Belongs to group 18 of the periodic table. Lowest boiling point of all elements and can only be solidified under pressure. Chemically inert, no known compounds. Discovered in the solar spectrum in 1868 by Lockyer.

Atomic Number	2
Atomic Weight	4.002602
Mass Number	4

Group	18
Period	1
Block	s

Protons	2 p⁺
Neutrons	2 n⁰
Electrons	2 e^-

Properties

Physical Properties
Atomic Radius	120 pm 134 pm
Molar Volume	31.8 cm³/mol
Covalent Radius	46 pm 28 pm
Metallic Radius	122 pm
Ionic Radius
Crystal Radius
Van der Waals Radius	140 pm 140 pm 153 pm 236.2 pm
Density	0.000164 g/cm³
Energy
Proton Affinity	177.8 kJ/mol
Electron Affinity	-19.7 eV/particle
Ionization Energy	24.587387936 eV/particle 54.41776311 eV/particle

Heat of Vaporization	0.08 kJ/mol
Heat of Fusion
Heat of Formation
Electrons
Electron Shells	2

Valence Electrons	2

Electron Configuration	1s²

Oxidation States
Electronegativity	24.59 eV/particle 0.442712
Electrophilicity	0.0674191963846371 eV/particle
Phases
Phase	Gas
Gas Phase	Monoatomic
Boiling Point	4.222 K
Melting Point
Critical Pressure	0.22746 MPa
Critical Temperature	5.195 K
Triple Point	2.177 K 5.043 kPa
Visual
Helium is a Colorless. He has a CPK of #ffc0cb, Jmol of #d9ffff, and MOLCAS GV of #d9ffff. The Appearance of Element 2 is colorless gas, exhibiting a red-orange glow when placed in a high-voltage electric field. The Refractive Index of Helium (He) is 1.000035.
Color	Colorless #ffc0cb #d9ffff #d9ffff
Appearance	colorless gas, exhibiting a red-orange glow when placed in a high-voltage electric field
Refractive Index	1.000035
Thermodynamic Properties
Thermal Conductivity	0.152 W/(m K)
Thermal Expansion
Molar Heat Capacity	20.786 J/(mol K)
Specific Heat Capacity	5.193 J/(g⋅K)
Heat Capacity Ratio (Adiabatic Index)	5/3
Electrical Properties
Type
Electrical Conductivity
Electrical Resistivity
Superconducting Point
Magnetism
Type	diamagnetic
Magnetic Susceptibility (Mass)	-0.0000000059 m³/Kg
Magnetic Susceptibility (Molar)	-0.0000000000236 m³/mol
Magnetic Susceptibility (Volume)	-0.00000000105
Magnetic Ordering
Curie Point
Neel Point
Structure
The Crystal Structure of Helium is HEX. The lattice constant of He is 3.57 Å. The lattice angles of Element 2 are π/2, π/2, π/2.
Crystal Structure	Face Centered Cubic (HEX)
Lattice Constant	3.57 Å
Lattice Angles	π/2, π/2, π/2
Mechanical Properties
The Speed of Sound of Helium is 970 m/s.
Hardness
Bulk Modulus
Shear Modulus
Young Modulus
Poisson Ratio
Speed of Sound	970 m/s
Classification
The CAS Group of Helium is VIII. The IUPAC Group of He is VIIIA. The Glawe Number of Element 2 is 1. The Mendeleev Number of Helium (He) is 112. The Pettifor Number of Helium is 1. The Geochemical Class of He is volatile. The Goldschmidt Class of Element 2 is atmophile.
Category	Noble gases, Noble gases
CAS Group	VIII
IUPAC Group	VIIIA
Glawe Number	1
Mendeleev Number	112
Pettifor Number	1
Geochemical Class	volatile
Goldschmidt Class	atmophile
Other
The Gas Basicity of Helium is 148.5 kJ/mol. The Dipole Polarizability of He is 1.38375 plus or minus 2.0E-5 a₀. Element 2 has a C6 Dispersion Coefficient (CD) of 1.42 a₀, and C6 Dispersion Coefficient (GB) of 1.47 a₀. The Allotropes of Helium (He) is . The Neutron Cross Section of Helium is 0.007. The Neutron Mass Absorption of He is 1.0E-5. The Quantum Numbers of Element 2 is 1S0. The Space Group of Helium (He) is 225 (Fm_3m).
Gas Basicity	148.5 kJ/mol
Dipole Polarizability	1.38375 ± 0.00002 a₀
C6 Dispersion Coefficient	1.42 a₀ 1.47 a₀
Allotropes
Neutron Cross Section	0.007
Neutron Mass Absorption	0.00001
Quantum Numbers	1S0
Space Group	225 (Fm_3m)

Isotopes of Helium

Stable Isotopes	2
Unstable Isotopes	6
Radioactive Isotopes	6

³He

Abundance	0.0002 ± 0.0002
Relative Atomic Mass	3.01602932197 ± 0.00000000006 Da
Mass Number	3
G-Factor	-4.25525062 ± 0.00000006
Half Life
Spin	1/2
Quadrupole Moment	0
Discovery Year	1934
Parity	+

⁴He

Abundance	99.9998 ± 0.0002
Relative Atomic Mass	4.00260325413 ± 0.00000000016 Da
Mass Number	4
G-Factor	0
Half Life
Spin	0
Quadrupole Moment	0
Discovery Year	1908
Parity	+

⁵He

Abundance	Radioactive ☢️
Relative Atomic Mass	5.012057224 ± 0.00002147 Da
Mass Number	5
G-Factor
Half Life	602 ± 22 ys
Spin	3/2
Quadrupole Moment
Discovery Year	1937
Parity	-

⁵He Decay Modes

Decay Mode	Intensity
n (neutron emission)	100%

⁶He

Abundance	Radioactive ☢️
Relative Atomic Mass	6.018885889 ± 0.000000057 Da
Mass Number	6
G-Factor	0
Half Life	806.92 ± 0.24 ms
Spin	0
Quadrupole Moment	0
Discovery Year	1936
Parity	+

⁶He Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%
β⁻ d (β⁻-delayed deuteron emission)	0.000278%

⁷He

Abundance	Radioactive ☢️
Relative Atomic Mass	7.027990652 ± 0.000008115 Da
Mass Number	7
G-Factor
Half Life	2.51 ± 0.07 zs
Spin	3/2
Quadrupole Moment
Discovery Year	1967
Parity

⁷He Decay Modes

Decay Mode	Intensity
n (neutron emission)	100%

⁸He

Abundance	Radioactive ☢️
Relative Atomic Mass	8.033934388 ± 0.000000095 Da
Mass Number	8
G-Factor	0
Half Life	119.5 ± 1.5 ms
Spin	0
Quadrupole Moment	0
Discovery Year	1965
Parity	+

⁸He Decay Modes

Decay Mode	Intensity
β⁻ (β⁻ decay)	100%
β⁻ n (β⁻-delayed neutron emission)	16%
β⁻ t (β⁻-delayed triton emission)	0.9%

⁹He

Abundance	Radioactive ☢️
Relative Atomic Mass	9.043946414 ± 0.000050259 Da
Mass Number	9
G-Factor
Half Life	2.5 ± 2.3 zs
Spin	1/2
Quadrupole Moment	0
Discovery Year	1987
Parity

⁹He Decay Modes

Decay Mode	Intensity
n (neutron emission)	100%

¹⁰He

Abundance	Radioactive ☢️
Relative Atomic Mass	10.052815306 ± 0.000099676 Da
Mass Number	10
G-Factor	0
Half Life	260 ± 40 ys
Spin	0
Quadrupole Moment	0
Discovery Year	1994
Parity	+

¹⁰He Decay Modes

Decay Mode	Intensity
2n (2-neutron emission)	100%

History

French astronomer Jules Janssen obtained the first evidence of helium during the solar eclipse of 1868. Norman Lockyer and Edward Frankland suggested the name helium for the new element. In 1895, Sir William Ramsay discovered helium in the uranium mineral cleveite. It was independently discovered in cleveite by Per Teodor Cleve and Abraham Langlet. From the Greek word helios, the sun

Discoverers	Sir William Ramsey, Nils Langet, P.T.Cleve
Discovery Location	Scotland/Sweden
Discovery Year	1895
Etymology (Name Origin)	Greek: hêlios (sun).
Pronunciation	HEE-li-em (English)

Helium is not known to be toxic

Unlike any other element, helium will remain liquid down to absolute zero at normal pressures

Uses

Helium is used as a protective gas in growing silicon and germanium crystals, in titanium and zirconium production, and in gas chromatography. Helium at low temperatures is used in cryogenics. Helium is used for filling balloons and for pressurizing liquid fuel rockets. Helium is used as a shielding gas in arc welding processes. Used in balloons, deep sea diving & welding. Also used in very low temperature research.

Sources

Found in natural gas deposits & in the air (5 parts per billion) Constantly lost to space; replenished by radioactive decay (alpha particles).

Abundance
Abundance in Earth's crust	0.008 mg/kg
Abundance in Oceans	0.000007 mg/L
Abundance in Human Body
Abundance in Meteor
Abundance in Sun	23 %
Abundance in Universe	23 %

Nuclear Screening Constants

0.3125

Helium on ChemicalAid

ATC code	V03AN03
Australian Educational Vocabulary ID	scot/3528
BNCF Thesaurus ID	19752
Bibliothèque nationale de France ID	11978648w
Brockhaus Enzyklopädie online ID	helium-20
CAB ID	178029
CAS Registry Number	7440-59-7
ChEBI ID	30217
ChEMBL ID	CHEMBL1796997
ChemSpider ID	22423
Common Procurement Vocabulary	24111300
DSSTOX compound identifier	DTXCID5016402
DSSTox substance ID	DTXSID7036402
De Agostini ID	èlio
Den Store Danske ID	helium
DrugBank ID	09155
ECHA Substance Infocard ID	100.028.334
Encyclopædia Britannica Online ID	science/helium-chemical-element
Encyclopædia Universalis ID	helium
E number	E939
Freebase ID	/m/025rt79
French Vikidia ID	Hélium
GND ID	4132459-6
Golden ID	Helium-K8NB
Great Russian Encyclopedia Online ID	2348591
HSDB ID	553
ICSC ID	0603
InChI	InChI=1S/He
InChIKey	SWQJXJOGLNCZEY-UHFFFAOYSA-N
Italian Vikidia ID	Elio
KBpedia ID	Helium
Klexikon article ID	Helium
Krugosvet article	nauka_i_tehnika/himiya/GELI.html
Library of Congress authority ID	sh85060043
MeSH descriptor ID	D006371
Mindat mineral ID	25563
NALT ID	44987
NDF-RT ID	N0000147379
NDL Authority ID	00563132
NE.se ID	helium
NKCR AUT ID	ph503003
Namuwiki ID	헬륨
National Library of Israel J9U ID	987007555644805171
OmegaWiki Defined Meaning	7296
Online PWN Encyclopedia ID	3910758
OpenAlex ID	C546029482
OpenAlex ID	C2991909631
PSH ID	5816
Probes And Drugs ID	PD009020
PubChem CID	23987
Quora topic ID	Helium
RxNorm ID	5140
Römpp online ID	RD-08-00783
Spanish Vikidia ID	Helio
Store norske leksikon ID	helium
Treccani ID	elio
U.S. National Archives Identifier	10640583
UMLS CUI	C0018880
UNII	206GF3GB41
USGS Thesaurus ID	1470
WordNet 3.1 Synset ID	14664099-n
World of Physics ID	Helium
YSO ID	14499
ZVG number	7020

Helium (He)

Properties

Isotopes of Helium

3He

4He

5He

5He Decay Modes

6He

6He Decay Modes

7He

7He Decay Modes

8He

8He Decay Modes

9He

9He Decay Modes

10He

10He Decay Modes