Element 12 · Magnesium (Mg)
Magnesium Bohr model: diagram and electrons per shell
The magnesium Bohr model shows a magnesium atom (Mg) as a small nucleus with its electrons circling it in 3 shells: 2 in shell K, 8 in shell L and 2 in shell M. This page has a rotating 3D magnesium Bohr model, a flat diagram, a table of the electrons in each shell and the steps to draw it yourself.
Rotate the magnesium Bohr model in 3D
Drag to orbit, scroll to zoom.
This is a Bohr model of magnesium (Mg), a simplified picture of a single magnesium atom. Its nucleus holds 12 protons, and a neutral magnesium atom has 12 electrons, arranged around it in 3 shells (2 in shell K, 8 in shell L and 2 in shell M).
Magnesium Bohr model diagram
Magnesium electrons per shell
A neutral magnesium atom has 12 electrons, one for each of its 12 protons. They fill the shells from the nucleus outwards: 2 in shell K, 8 in shell L and 2 in shell M.
| Shell | Shell number (n) | Electrons | Most it can hold (2n²) | Subshells |
|---|---|---|---|---|
| K | 1 | 2 | 2 | 1s2 |
| L | 2 | 8 | 8 | 2s2 2p6 |
| M | 3 | 2 | 18 | 3s2 |
How the magnesium Bohr model builds up, shell by shell
Watch the magnesium 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 and 2 in shell M) as it forms.
How to draw the magnesium Bohr model
- Find the atomic number. Magnesium has atomic number 12, so a neutral atom has 12 protons and 12 electrons.
- Draw the nucleus. Put a circle in the centre and write Mg in it. The 12 protons sit there with the neutrons.
- Draw the shells. Sketch 3 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 and 2 in shell M.
- Check the total. 2 + 8 + 2 = 12, the atomic number, so every electron is accounted for.
Atomic data for the magnesium Bohr model
The numbers behind the magnesium Bohr model, grouped by topic. Radii are in picometres (pm) and energies in kilojoules per mole (kJ/mol).
Identity
- Symbol
- Mg
- Atomic number
- 12
- Atomic mass
- 24.305 u
- Family
- Alkaline Earth Metals
- Position
- group 2, period 3
- Block
- s-block
Electron configuration
- Full
- 1s2 2s2 2p6 3s2
- Shorthand
- [Ne] 3s2
- Electrons per shell
- 2, 8, 2
- Outer-shell electrons
- 2 in shell M
Ionisation energies
- I₁
- 737.7
- I₂
- 1450.7
- I₃
- 7732.7
- I₄
- 10542.5
- I₅
- 13630
- I₆
- 18020
- I₇
- 21711
- I₈
- 25661
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)
- 145
- Empirical (pm)
- 150
- Covalent (pm)
- 139
- Van der Waals (pm)
- 173
Electronegativity and electron affinity
- Electronegativity (Pauling)
- 1.31
- Electron affinity (kJ/mol)
- -40
Oxidation states
+2
Charges the element commonly takes in compounds.
Physical properties, abundance and history of magnesium
Bulk properties of magnesium, how common it is, who discovered it and some of its compounds.
Physical properties
- Phase at room conditions
- Solid
- Appearance
- Shiny grey solid
- Melting point
- 649.85°C (923 K)
- Boiling point
- 1089.85°C (1363 K)
- Density
- 1.738 g/cm³
- Thermal conductivity (W/m·K)
- 156
- Specific heat (J/g·K)
- 1.023
- Molar heat capacity (J/mol·K)
- 24.869
- Heat of fusion (kJ/mol)
- 9.2
- Heat of vaporisation (kJ/mol)
- 131.8
Abundance
- Earth's crust (mg/kg)
- 23300
- Oceans (mg/L)
- 1290
Discovery
- Discovered by
- Joseph Black
- Year
- 1755
Common compounds
- Magnesium Oxide MgO
- Magnesium Mg
- Sulfuric acid magnesium salt (1:1) MgO4S
- Magnesium Chloride Cl2Mg
- Magnesium Cation Mg+2
- Magnesium Hydroxide H2MgO2
- Chlorophyllin C34H34MgN4O6
- Magnesium Carbonate CMgO3
Compounds listed in the PubChem database.
Main isotopes of magnesium
Isotopes of magnesium share the same 12 protons but differ in neutrons. Natural isotopes come first, then the longest-lived others.
| Mass number | Natural abundance | Half-life | Decay |
|---|---|---|---|
| 23 | – | 11.304 s | β⁺ |
| 24 | 78.965 % | stable | – |
| 25 | 10.011 % | stable | – |
| 26 | 11.025 % | stable | – |
| 27 | – | 9.435 min | β⁻ |
| 28 | – | 20.915 h | β⁻ |
α = alpha decay, β⁻ = beta-minus, β⁺ = beta-plus, EC = electron capture, SF = spontaneous fission, p / n = proton / neutron emission.
More about magnesium
- Magnesium on the periodic table – properties, isotopes, uses and the full magnesium page.
- Alkaline Earth Metals – all alkaline earth metal elements and their trends.
- Bohr model of every element – the Bohr model of all 118 elements.