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Helium

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Helium Quick Reference

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Notes

Symbol

He

Atomic Number

2

Atomic Weight

Rounded

4.0026

for regular calculations

Standard

4.002602 ± 0.000002

for precise calculations

Oxidation States

0

Electron Configuration

Orbital Occupancy

1s2

Orbital Filling Order

1s2

Term Symbol

1S0

see expanded configuration ...

Ionization Energies

I  (1)

24.587387 eV

II (2)

54.417760 eV

Electron Affinity

<0 eV

<0 cm-1

Density

gas

25 °C, 1 atm

0.1636 g/L 

273.15 K, 1 atm

0.1786 g/L 

solid, 2 K, 37 atm

0.205 g/cm3

helium-4, liquid

4.21 K

0.125 g/ml 

1.76 K

0.152 g/ml 

helium-3, liquid, 3.19 K

0.055 g/ml 

Molar Volume

gas, 273.15 K, 1 atm

22.4136 L/mol

Melting Point

26 atm

0.95 K

33.3 bar

1.86 K

Boiling Point

1 atm

4.22 K

helium-4, 1 atm

4.21 K

helium-3, 1 atm

3.19 K

Thermal Conductivity

gas

400 K, 1 atm

0.1870 W/(m K)

300 K, 1 atm

0.1520 W/(m K)

290 K, 1 atm

0.1484 W/(m K)

280 K, 1 atm

0.1447 W/(m K)

270 K, 1 atm

0.1411 W/(m K)

200 K, 1 atm

0.1151 W/(m K)

see all 55 conductivities ...

Pyykkö Covalent Radius

single bond

46 pm

Enthalpy of Vaporization

1 atm

0.082 kJ/mol

Quantity

Helium Atomic Structure

Notes

Ionization Energies

I  (1)

24.587387 eV

II (2)

54.417760 eV

Electron Affinity

<0 eV

<0 cm-1

Electron Binding Energies

(1s)

24.6 eV

Electron Configuration

Orbital Occupancy

1s2

Orbital Filling Order

1s2

Term Symbol

1S0

see expanded configuration ...

Clementi-Raimondi Effective Nuclear Charge

1s

Orbital Exponent

1.6875

ζ

Principle Quantum Number

1

n

Effective Nuclear Charge

1.6875

Zeff = ζ × n

Screening Percentage

15.0%

Fluorescence Yields

ωK

0.0001

Quantity

Helium Physical Properties

Notes

Density

gas

25 °C, 1 atm

0.1636 g/L 

273.15 K, 1 atm

0.1786 g/L 

solid, 2 K, 37 atm

0.205 g/cm3

helium-4, liquid

4.21 K

0.125 g/ml 

1.76 K

0.152 g/ml 

helium-3, liquid, 3.19 K

0.055 g/ml 

Molar Mass

Rounded

4.0026 g/mol

for regular calculations

Standard

4.002602 ± 0.000002 g/mol

for precise calculations

Molar Volume

gas, 273.15 K, 1 atm

22.4136 L/mol

Physical Form

colorless gas

Speed of Sound

gas

273.2 K

971.9 m/s

0 °C, 1 atm

965 m/s  

liquid

-268.9 °C

180 m/s  

-269 °C, longitudinal wave

211 m/s  

Dielectric Constant

liquid

1.05    

20 °C, 1 atm

1.000068

2.06 K

1.06    

helium-3, 58 °F

1.065   

Gram Atomic Volume

32 cm3

Quantity

Helium Atomic Interaction

Notes

Oxidation States

0

Mulliken-Jaffe Electronegativity

orbitals

3.49

Allred-Rochow Electronegativity

5.50

Configuration Energy

electron volt units

24.59 eV

Pauling units

 4.160  

Ghosh-Gupta Electronegativity

12.0568 eV

Nagle Electronegativity

3.92

Quantity

Helium Thermodynamics

Notes

Melting Point

26 atm

0.95 K

33.3 bar

1.86 K

Boiling Point

1 atm

4.22 K

helium-4, 1 atm

4.21 K

helium-3, 1 atm

3.19 K

Thermal Conductivity

gas

400 K, 1 atm

0.1870 W/(m K)

300 K, 1 atm

0.1520 W/(m K)

290 K, 1 atm

0.1484 W/(m K)

280 K, 1 atm

0.1447 W/(m K)

270 K, 1 atm

0.1411 W/(m K)

200 K, 1 atm

0.1151 W/(m K)

see all 55 conductivities ...

Critical Point

helium-4

temperature

5.19 K

pressure

2.29 bar

helium-3

temperature

3.32 K

pressure

1.16 bar

Vapor Pressure

-268.9 °C

100 kPa

2.5 K

10.23 kPa

2.0 K

3.130 kPa

see all 21 pressures ...

Enthalpy of Vaporization

1 atm

0.082 kJ/mol

Isobaric Molar Heat Capacity

298.15 K, 1 bar

20.786 J/(mol K)

Isobaric Specific Heat Capacity

298.15 K, 1 bar

5.193 J/(g K)

Quantity

Helium Identification

Notes

CAS Number

7440-59-7

DOT Number

1046

compressed

1046

refrigerated liquid (cryogenic liquid)

1963

ICSC Number

0603

RTECS Number

MH6520000

UN Number

1963

Quantity

Helium Atomic Size

Notes

Orbital Radius

29.1 pm

Pyykkö Covalent Radius

single bond

46 pm

Cordero Covalent Radius

28 pm

Pauling Univalent Radius

ion charge: 0

93 pm

Bondi Van Der Waals Radius

140 pm

Quantity

Helium Crystal Structure

Notes

Allotropes

allotrope

α-helium

symbol

αHe

allotrope

β-helium

symbol

βHe

allotrope

γ-helium

symbol

γHe

Quantity

Helium History

Notes

Discovery

date of discovery

1895

discoverer

William Ramsay

birth

October 2, 1852

death

July 23, 1916

location of discovery

London, England

Origin of Element Name

origin

Helios

origin description

celestial body—Greek for Sun

Origin of Element Symbol

symbol: He

origin

helium

origin description

element name

Quantity

Helium Abundances

Notes

Earth's Crust

8×10-3 ppm

Earth's Atmosphere

5.24 ppm

Ocean Water

7.2×10-6 ppm

Universe

0.097

relative to hydrogen = 1.00000

Solar System

2.72×109

number of atoms for every 106 atoms of silicon

Sun

10.93 ± 0.004

base 10 log of the number of atoms for every 1012 atoms of hydrogen

Quantity

Helium Nomenclature

Notes

Element Names in Other Languages

French

hélium

German

Helium

Italian

elio

Spanish

helio

Portuguese

hélio

Anions or Anionic Substituent Groups

helide

Cations or Cationic Substituent Groups

helium (general)

He•+, helium(•1+)

Ligands

helido

Heteroatomic Anion

helate

'a' Term—Substitutive Nomenclature

hela

'y' Term—Chains and Rings Nomenclature

hely

References    (Click the button next to a value above to see complete citation information for that entry)

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