Elements
Helium ( He )
- Atomic number: 2
- Appearance: colorless gas
- Standard atomic weight: 4.002602
- Group: group 18 (noble gases)
- Period: 1
- Electron configuration: 1s2
- Element category: noble gas
- Melting point: 0.95 K
- Boiling point: 4.222 K
- Sublimation point: Standard Temperature ( 273.15 ) and Pressure ( 1 bar = 105 Pa )
- Phase at STP: gas
- Density at STP:
- Heat of fusion: 0.0138 kJ/mol
- Heat of vaporization: 0.0829 kJ/mol
- Molar heat capacity: 20.78 kJ/(mol·K)
- Oxidation states: 0
- Electronegativity: Pauling scale: no data
- Covalent radius: 28 pm (1×10−12 m)
- Van der Waals radius: 140 pm (1×10−12 m)
- Crystal structure: hexagonal close-packed
- Speed of sound: 972 m/s (gas, 27 °C)
- Thermal expansion:
- Thermal conductivity: 0.1513 W/(m·K)