Element 20 · Calcium (Ca)
Calcium Bohr model: diagram and electrons per shell
The calcium Bohr model shows a calcium atom (Ca) as a small nucleus with its electrons circling it in 4 shells: 2 in shell K, 8 in shell L, 8 in shell M and 2 in shell N. This page has a rotating 3D calcium Bohr model, a flat diagram, a table of the electrons in each shell and the steps to draw it yourself.
Rotate the calcium Bohr model in 3D
Drag to orbit, scroll to zoom.
This is a Bohr model of calcium (Ca), a simplified picture of a single calcium atom. Its nucleus holds 20 protons, and a neutral calcium atom has 20 electrons, arranged around it in 4 shells (2 in shell K, 8 in shell L, 8 in shell M and 2 in shell N).
Calcium Bohr model diagram
Calcium electrons per shell
A neutral calcium atom has 20 electrons, one for each of its 20 protons. They fill the shells from the nucleus outwards: 2 in shell K, 8 in shell L, 8 in shell M and 2 in shell N.
| Shell | Shell number (n) | Electrons | Most it can hold (2n²) | Subshells |
|---|---|---|---|---|
| K | 1 | 2 | 2 | 1s2 |
| L | 2 | 8 | 8 | 2s2 2p6 |
| M | 3 | 8 | 18 | 3s2 3p6 |
| N | 4 | 2 | 32 | 4s2 |
How the calcium Bohr model builds up, shell by shell
Watch the calcium Bohr model come together: the nucleus first, then each shell in turn, from the innermost outwards, with its electrons joining the ring. The legend names every shell and counts its electrons, so you can read off the arrangement (2 in shell K, 8 in shell L, 8 in shell M and 2 in shell N) as it forms.
How to draw the calcium Bohr model
- Find the atomic number. Calcium has atomic number 20, so a neutral atom has 20 protons and 20 electrons.
- Draw the nucleus. Put a circle in the centre and write Ca in it. The 20 protons sit there with the neutrons.
- Draw the shells. Sketch 4 shells as rings around the nucleus. A shell holds at most 2n² electrons: 2 in the first, 8 in the second, 18 in the third and 32 in the fourth.
- Place the electrons. Fill from the inside out: 2 in shell K, 8 in shell L, 8 in shell M and 2 in shell N.
- Check the total. 2 + 8 + 8 + 2 = 20, the atomic number, so every electron is accounted for.
Atomic data for the calcium Bohr model
The numbers behind the calcium Bohr model, grouped by topic. Radii are in picometres (pm) and energies in kilojoules per mole (kJ/mol).
Identity
- Symbol
- Ca
- Atomic number
- 20
- Atomic mass
- 40.0784 u
- Family
- Alkaline Earth Metals
- Position
- group 2, period 4
- Block
- s-block
Electron configuration
- Full
- 1s2 2s2 2p6 3s2 3p6 4s2
- Shorthand
- [Ar] 4s2
- Electrons per shell
- 2, 8, 8, 2
- Outer-shell electrons
- 2 in shell N
Ionisation energies
- I₁
- 589.8
- I₂
- 1145.4
- I₃
- 4912.4
- I₄
- 6491
- I₅
- 8153
- I₆
- 10496
- I₇
- 12270
- I₈
- 14206
Energy to remove each electron in turn (kJ/mol). A sharp jump means the next electron comes from an inner shell.
Atomic radii
- Calculated (pm)
- 194
- Empirical (pm)
- 180
- Covalent (pm)
- 171
- Van der Waals (pm)
- 231
Electronegativity and electron affinity
- Electronegativity (Pauling)
- 1
- Electron affinity (kJ/mol)
- 2.37
Oxidation states
+2
Charges the element commonly takes in compounds.
Physical properties, abundance and history of calcium
Bulk properties of calcium, how common it is, who discovered it and some of its compounds.
Physical properties
- Phase at room conditions
- Solid
- Melting point
- 841.85°C (1115 K)
- Boiling point
- 1483.85°C (1757 K)
- Density
- 1.55 g/cm³
- Specific heat (J/g·K)
- 0.647
- Molar heat capacity (J/mol·K)
- 25.929
- Heat of fusion (kJ/mol)
- 9.2
- Heat of vaporisation (kJ/mol)
- 153.6
Abundance
- Earth's crust (mg/kg)
- 41500
- Oceans (mg/L)
- 412
Discovery
- Discovered by
- Humphry Davy
- Year
- 1808
Common compounds
- Calcium Chloride CaCl2
- Calcium propionate C6H10CaO4
- Calcium Lactate C6H10CaO6
- Edetate Calcium Disodium Anhydrous C10H12CaN2Na2O8
- Calcium Pantothenate C18H32CaN2O10
- Calcium Hydroxide CaH2O2
- Calcium Carbonate CCaO3
- Calcium Acetate C4H6CaO4
Compounds listed in the PubChem database.
Main isotopes of calcium
Isotopes of calcium share the same 20 protons but differ in neutrons. Natural isotopes come first, then the longest-lived others.
| Mass number | Natural abundance | Half-life | Decay |
|---|---|---|---|
| 40 | 96.941 % | stable | 2β⁺ |
| 42 | 0.647 % | stable | – |
| 43 | 0.135 % | stable | – |
| 44 | 2.086 % | stable | – |
| 46 | 0.004 % | stable | 2β⁻ |
| 48 | 0.187 % | 56 Ey | 2β⁻, β⁻ |
α = alpha decay, β⁻ = beta-minus, β⁺ = beta-plus, EC = electron capture, SF = spontaneous fission, p / n = proton / neutron emission.
More about calcium
- Calcium on the periodic table – properties, isotopes, uses and the full calcium page.
- Alkaline Earth Metals – all alkaline earth metal elements and their trends.
- Bohr model of every element – the Bohr model of all 118 elements.