Magnesium (Mg): Bohr Model, Protons, Neutrons & Electrons
Magnesium is element number 12, an alkaline earth metal in group 2, period 3. Its atom has 12 protons, 12 neutrons and 12 electrons arranged in 3 shells: 2, 8, 2.
Protons, neutrons and electrons in magnesium
The atomic number of magnesium is 12, so every magnesium atom has 12 protons. A neutral atom has the same number of electrons, 12. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For magnesium-24, that is 24 − 12 = 12 neutrons. Magnesium has 3 stable isotopes, with 12, 13, 14 neutrons.
How to draw the Bohr model of magnesium
- Draw the nucleus and write 12 p⁺ and 12 n⁰ inside it.
- Draw the first shell and put 2 electrons on it (the first shell holds at most 2).
- Draw the second shell and put 8 electrons on it.
- Draw the third shell and put 2 electrons on it.
- Check: 2 + 8 + 2 = 12 electrons, the same as the number of protons.
Electron configuration
The electron configuration of magnesium is [Ne] 3s². Its 2 outer electrons decide how it reacts: it tends to lose them, forming Mg²⁺ ions.
Key facts about magnesium
| Symbol | Mg |
|---|---|
| Atomic number | 12 |
| Relative atomic mass | 24.305 |
| Group · period · block | group 2 · period 3 · s-block |
| Type | Alkaline Earth Metal |
| State at 25 °C | solid |
| Electron shells | 2, 8, 2 |
| Electron configuration | [Ne] 3s² |
| Valence electrons | 2 |
| Common ion | Mg²⁺ |
| Electronegativity (Pauling) | 1.31 |
| First ionisation energy | 7.65 eV (738 kJ/mol) |
| Atomic radius (empirical) | 150 pm |
Where magnesium sits on the periodic table
Frequently asked questions
How many protons, neutrons and electrons does magnesium have?
Magnesium has 12 protons and 12 electrons (atomic number 12). Its most common isotope, magnesium-24, has 24 − 12 = 12 neutrons.
What is the electron configuration of magnesium?
[Ne] 3s². In shells that is 2, 8, 2.
How many valence electrons does magnesium have?
2. Magnesium is in group 2, and its outer shell holds 2 electrons.
Where is magnesium on the periodic table?
In group 2, period 3, in the s-block. It is an alkaline earth metal.
