• Class: Inert Gases
• Period: 1
• IUPAC group: 18
• Traditional: 0

• Discovered in: 1868 by Janssen
• Origin of name: Greek: helios, (the sun)
• Historical or alternate name:

Atmosphere, 1 part in 200,000; radioactive minerals as a decay product

Colorless, odorless gas; nonreactive chemically.

• Atmosphere: 5.2 ppm
• Primitive mantle: ~0.0 ppm
• Sea water: 7.2e-6 ppm
• Metallic meteorite: 56000.0 ppm
• Continental crust: 0.008 ppm
• Solar photosphere: 10.8 log of abundance
• Oceanic crust: ~0.0 ppm
• Solar system: 2.180E+9 relative to Si=1.0e6

   Hazards

Inert nonflammable gas. Asphyxiant..

   Human daily limits

• Lower:
• Upper:0.95

Helium Physical Properties

 Transitional Data

• State: Gas
• Density: 0.1785 g/L

 Molar enthalpy

• Atomization: 0.0 kJ mol-1
• Fusion: 0.021 kJ mol-1
• Vaporization: 0.082 kJ mol-1

 Transition points

• Melting point: 0.95 K
• Boiling point: 4.22 K
• Critical temperature: 5.19 K

 Molar properties

• Atomic weight: 4.002602 g/mole
• Molar volume: 19.61 cm3 mol-1

 Crystal structure sequence

body-centered-cubic -> hexagonal-close-packed -> face-centered-cubic with increasing pressure

 Thermodynamics

• State: gas
  • Enthalpy 0
  • Gibbs function 0
  • Entropy 126.150
  • Heat Capacity 20.786

 Miscellaneous physical

• Electrical resistivity: µ-ohms/cm
• Debye temperature: K
• Thermal conductivity: 0.155 W / m / K
• Coefficient of linear expansion: Coef. per K
• Mass magnetic susceptibility: -5.9e-9
• X-ray diffraction mass absorption coefficients:
• CuK: 0.383 (µ/p)/cm2 g-1
• MoK: 0.207 (µ/p)/cm2 g-1

Helium Chemical Properties

 Chemical basics:

• Oxidation states: 0
• Molecular wt: 4.002602 g/mole

 Radii

• Covalent: pm
• Atomic: 128 pm
• Van der Waals: 122 pm

 Ions:

 Covalent bonds

 Effective nuclear charge

• Slater: 1.70
• Clementi: 1.69
• Froese-Fischer: 1.62

 Electronegativity

• Pauling:
• Allred-Rochow:

 Standard reactions

Helium Nuclear Properties

• Known 5
• Listed 2

• Known 3 - 8
• Listed 3 - 4

• % Occ.:Natural 0.000138%
• Mossbauer NRA:
• Nuclear spin/Quantum no.: 1/2
• Radioisotopes:
  • Half-life:
  • Decay mode:
  • Source:
• Notes

• % Occ.:Natural 99.999862%
• Mossbauer NRA:
• Nuclear spin/Quantum no.:
• Radioisotopes:
  • Half-life:
  • Decay mode:
  • Source:
• Notes

• Isotope Cross-section 0.007 barns

• Absolute sensitivity: 5.75e-7 1H=1.0
• Relative sensitivity: 0.44 1H=1.0
• Receptivity: 0.00326 13C=1.0
• Magnetogyric ratio: -20.378e7 rad / T / s
• Quadropole moment: m2
• Frequency: 76.178 MHz
• Reference:

Helium Energy Properties

Electrons

• Ground state electron configuration: 1s2
• Electron affinity: -21 kJ mol-1
• Filling orbitals:

 Ionization energies

 Atomic energy levels