20Ca40.078
Calcium
Alkaline earth metalsBlock sPeriod 4Group 2solid at 20 °C
- Configuration :
- [Ar] 4s²
- Atomic mass :
- 40.078 u
3D Bohr-model representation of the Calcium atom (symbol Ca, atomic number Z=20). Electron shell configuration: 2, 8, 8, 2 electrons.
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Bohr model · educational
Bohr model of calcium
Calcium (Ca) has 20 electrons, spread over 4 shells. The diagram places them on circles around the nucleus, from the K shell — the closest — outward.
| Shell | Electrons |
|---|---|
| K (n = 1) | 2 |
| L (n = 2) | 8 |
| M (n = 3) | 8 |
| N (n = 4) | 2 |
The Bohr model is a teaching picture: electrons do not travel in circular orbits, but the number of electrons per shell is exact.
Related lesson
Atoms, molecules, ions
When an atom bonds to another, it forms a molecule. When it loses or gains an electron, it becomes an ion. First examples.
8 minElectron configuration
Full1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
Short[Ar] 4s²
Valence electrons2
KLMNOPQ shells
K2
L8
M8
N2
Electronegativity
Pauling1
Allen1.034
Mulliken (eV)—
Atomic radii
Empirical180 pm
Calculated194 pm
Covalent176 pm
Van der Waals231 pm
Ionic radii (Shannon-Prewitt)
+2100 pm
Successive ionisation energies
I₁589.8 kJ/mol
I₂1145.4 kJ/mol
I₃4912.4 kJ/mol
I₄6491 kJ/mol
I₅8153 kJ/mol
Electron affinity2.37 kJ/mol
Oxidation states
+1+2
Bold states = most common.
Warm-up
Calcium — do you remember?
3 questions on this page. The right answer shows every time, and nothing is asked of you to play.
No account · one minute