Aluminium vs Magnesium
Aluminium is a metal (post-transition metal); Magnesium is a metal (alkaline earth metal).
The differences in plain English
- They share period 3, the same row, so their outer electrons are in the same shell but they differ in how many there are: Aluminium has 3, Magnesium has 2.
- Both are solids at room temperature.
- Aluminium is denser, about 55 per cent more than Magnesium (2.7 against 1.738 g/cm³).
- Aluminium melts at 660 °C, Magnesium at 650 °C.
- An atom of Aluminium is only slightly heavier than an atom of Magnesium (26.98 u against 24.30 u).
- Aluminium pulls electrons more strongly in a bond (electronegativity 1.61 against 1.31).
Side by side
| Aluminium | Magnesium | |
|---|---|---|
| Atomic number | 13 | 12 |
| Symbol | Al | Mg |
| Family | Post-transition metal | Alkaline earth metal |
| Group / period | 13 / 3 | 2 / 3 |
| State at room temperature | Solid | Solid |
| Atomic mass | 26.982 u | 24.305 u |
| Density | 2.7 g/cm³ | 1.738 g/cm³ |
| Melting point | 660 °C | 650 °C |
| Boiling point | 2470 °C | 1090 °C |
| Electronegativity | 1.61 | 1.31 |
| First ionisation energy | 577.5 kJ/mol | 737.7 kJ/mol |
| Electron configuration | [Ne] 3s2 3p1 | [Ne] 3s2 |
| Discovered by | Joseph Black |
Aluminium
Aluminium is the most abundant metal in the Earth's crust, yet two hundred years ago nobody had seen a piece of it. It clings so tightly to oxygen that separating it needed chemistry that did not yet exist. Then cheap electricity changed everything, and today it is the second most used metal in the world.
- In the 1850s aluminium cost more than gold, and Napoleon III is said to have served his most honoured guests with aluminium cutlery.
- The small pyramid on top of the Washington Monument, set in 1884, is made of aluminium, then a showpiece metal.
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.