2He4.003
Noble Gass-block
Helium
Element 2 on the periodic table, symbol He, group 18, period 1.
Helium is a chemical element with symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table. Its boiling and melting points are the lowest among all the elements.
Appearance: colorless gas, exhibiting a red-orange glow when placed in a high-voltage electric field
Properties
- Atomic Number
- 2
- Atomic Mass
- 4.0026 u
- Group
- 18
- Period
- 1
- Block
- s-block
- Category
- Noble Gas
- State at 25 °C
- Gas
- Melting Point
- 1 K · -272.2 °C
- Boiling Point
- 4.2 K · -268.9 °C
- Density
- 0.1786 g/L
- Atomic Radius
- 31 pm
- Electronegativity
- Not measured
- Oxidation States
- None commonly seen
- Abundance in Crust
- 0.008 mg/kg
- Discovered
- 1868
- Discovered By
- Pierre Janssen
Electron Configuration
1s2
1s2
Ionisation Energies (kJ/mol)
- 1. 2,372.3
- 2. 5,250.5
Elements near Helium
Elements in the same group share the number of outer electrons and behave in similar ways. Elements in the same period share a shell, so they change steadily from left to right.