Calcium vs Magnesium
Both are alkaline earth metals, so they share the same broad chemistry.
The differences in plain English
- They sit in the same column, group 2, so they have the same number of outer electrons and react in similar ways; the heavier one, Calcium, is usually the more reactive of the two if they are metals, and the less reactive if they are non-metals.
- Both are solids at room temperature.
- Magnesium is denser, only slightly more than Calcium (1.738 against 1.55 g/cm³).
- Calcium melts at 842 °C, Magnesium at 650 °C.
- An atom of Calcium is about 65 per cent heavier than an atom of Magnesium (40.08 u against 24.30 u).
- Magnesium pulls electrons more strongly in a bond (electronegativity 1.31 against 1).
Side by side
| Calcium | Magnesium | |
|---|---|---|
| Atomic number | 20 | 12 |
| Symbol | Ca | Mg |
| Family | Alkaline earth metal | Alkaline earth metal |
| Group / period | 2 / 4 | 2 / 3 |
| State at room temperature | Solid | Solid |
| Atomic mass | 40.078 u | 24.305 u |
| Density | 1.55 g/cm³ | 1.738 g/cm³ |
| Melting point | 842 °C | 650 °C |
| Boiling point | 1484 °C | 1090 °C |
| Electronegativity | 1 | 1.31 |
| First ionisation energy | 589.8 kJ/mol | 737.7 kJ/mol |
| Electron configuration | [Ar] 4s2 | [Ne] 3s2 |
| Discovered by | Humphry Davy | Joseph Black |
Calcium
You are carrying about a kilogram of calcium, almost all of it in your bones and teeth. Yet calcium the metal is something few people ever see: a soft, silvery solid that fizzes gently in water and dulls quickly in air. The metal is a curiosity. Its compounds are everywhere, in chalk, limestone, marble, seashells, cement, plaster and indigestion tablets.
- Cement manufacture is one of the largest single industrial sources of carbon dioxide, because heating limestone drives off the gas chemically as well as burning fuel.
- Calcium colours a flame brick red, which is how it shows up in a flame test and in some fireworks.
Magnesium
Magnesium is a light, silvery metal best known for the dazzling white flame it produces when it burns. Yet the same element, in a gentler form, sits at the centre of the chlorophyll molecule that lets plants capture sunlight. Without it there would be no photosynthesis, and so no food.
- Every chlorophyll molecule has a magnesium ion at its centre, so photosynthesis depends on magnesium.
- Burning magnesium cannot be extinguished with water or carbon dioxide because it reacts with both.
Colour the bubbles by density or melting point and the difference jumps out.
More comparisons
Data from Periodic-Table-JSON (CC BY-SA); temperatures rounded to the nearest degree. Written by Anthony.