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2He4.00260
Helium
Noble gasesBlock sPeriod 1Group 18gas at 20 °C
- Configuration :
- 1s²
- Atomic mass :
- 4.002602 u
- French :
- Hélium
3D Bohr-model representation of the Helium atom (symbol He, atomic number Z=2). Electron shell configuration: 2 electrons.
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Bohr model · educational
Related lesson
First look at the periodic classification
Reading the table, spotting families (alkali metals, halogens, noble gases). Why some elements share properties.
9 minElectron configuration
Full1s²
Short1s²
Valence electrons2
KLMNOPQ shells
K2
Electronegativity
Pauling—
Allen4.16
Mulliken (eV)—
Atomic radii
Empirical120 pm
Calculated31 pm
Covalent28 pm
Van der Waals140 pm
Successive ionisation energies
I₁2372.3 kJ/mol
I₂5250.5 kJ/mol
Electron affinity—
Oxidation states
0
Bold states = most common.