Magnesium (Mg)
Magnesium is element 12, an alkaline earth metal in group 2, period 3. A neutral atom has 12 protons, 12 neutrons and 12 electrons, 2 of them valence electrons.
Alkaline earth metal- Atomic number
- 12
- Atomic mass
- 24.305 u
- Valence electrons
- 2
- Protons · neutrons
- 12 · 12
- Electrons per shell
- 2, 8, 2
- At room temperature
- solid
Bohr model of magnesium
The Bohr model draws magnesium as a nucleus of 12 protons and 12 neutrons, with its 12 electrons on 3 circular shells: 2 in shell 1, 8 in shell 2, 2 in shell 3. Press Build the atom to watch the shells fill from the inside out. The outer ring (the M shell) is dashed: the electrons there are the ones that take part in chemistry.
Real electrons don't travel in neat circles. They live in fuzzy orbitals, shown below, but the Bohr picture is the quickest way to count shells and valence electrons.
Electron configuration of magnesium
1s² 2s² 2p⁶ 3s²
Short form (noble gas notation): [Ne] 3s². The [Ne] stands for the electrons of neon, the noble gas before it.
How many valence electrons does magnesium have?
Magnesium has 2 valence electrons.
Magnesium is in group 2, so it has 2 valence electrons. It tends to lose them and form a +2 ion.
Protons, neutrons and electrons
| Protons | 12 | equal to the atomic number |
|---|---|---|
| Electrons | 12 | equal to the protons in a neutral atom |
| Neutrons | 12 | mass number 24 − 12 protons |
Atoms of the same element can have different numbers of neutrons (isotopes). The count above uses the rounded atomic mass, the way it's taught in class.
Magnesium properties
| Symbol | Mg |
|---|---|
| Category | Alkaline earth metal |
| Group · period · block | 2 · 3 · s |
| Atomic mass | 24.305 u |
| State at 25 °C | solid |
| Melting point | 923 K (650 °C, 1,200 °F) |
| Boiling point | 1,363 K (1,090 °C, 1,990 °F) |
| Density | 1.74 g/cm³ |
| Electronegativity (Pauling) | 1.31 |
| Atomic radius | 173 pm |
| First ionization energy | 7.646 eV |
| Electron affinity | — |
| Oxidation states | +2 |
| Common ion charge | +2 |
| Discovered | 1808 by Joseph Black |
Where magnesium sits on the periodic table
Group 2: Beryllium, Calcium, Strontium, Barium, Radium.
Questions about magnesium
How many valence electrons does magnesium have?
Magnesium has 2 valence electrons.
How many protons, neutrons and electrons does magnesium have?
A neutral magnesium atom has 12 protons and 12 electrons. Its most common form has about 12 neutrons (mass number 24 − 12 protons).
What is the electron configuration of magnesium?
1s² 2s² 2p⁶ 3s², written in short form as [Ne] 3s².
What does the Bohr model of magnesium look like?
A nucleus of 12 protons and 12 neutrons, circled by 3 electron shells holding 2, 8, 2 electrons.
What is the atomic number of magnesium?
12. The atomic number is the number of protons in the nucleus, and it is what makes an atom magnesium.