Magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It has a standard atomic weight of 24.305, sits in period 3 and group 2, and is classified as an alkaline earth metal.
Properties
| Symbol | Mg |
|---|---|
| Atomic number | 12 |
| Standard atomic weight | 24.305 |
| Category | Alkaline earth metal |
| Group | 2 |
| Period | 3 |
| Electron configuration | [Ne] 3s2 |
| Outer-shell electrons | 2 |
The figure of 24.305 is a conventional value, because IUPAC publishes an interval for this element rather than a single weight. For elements like this one the fourth digit carries real uncertainty, because the isotopic composition varies measurably between natural sources — so quoting eight digits would overstate what is known.
Compounds containing magnesium
6 of the compounds in this reference contain Mg, listed by the fraction of their mass it makes up.
| Compound | Formula | Atoms | % by mass |
|---|---|---|---|
| magnesium oxide | MgO | 1 | 60.3% |
| magnesium hydroxide | H2MgO2 | 1 | 41.7% |
| magnesium chloride | Cl2Mg | 1 | 25.5% |
| magnesium sulfate | MgO4S | 1 | 20.2% |
| epsom salt | H14MgO11S | 1 | 9.9% |
| chlorophyll a | C55H72MgN4O5 | 1 | 2.7% |
Calculate with magnesium
- Molar mass of any formula containing it
- Electron configuration, including ions
- Effective nuclear charge by Slater's rules
- Average atomic mass from isotope abundances
Group 2
Atomic weights are the IUPAC 2021 standard values, abridged to the conventional five significant figures. Group, period, category and electron configuration are derived from the atomic number rather than stored, so they cannot drift out of step with it.