20Ca40.078
Calcium
Alkaline earth metalsReactive metals with two outer electrons, found in rocks, shells and bones.
[Ar] 4s²
- Atomic number
- 20
- Atomic mass
- 40.078
- Protons
- 20
- Neutrons
- 20 (most common)
- Electrons
- 20
- Shells
- 2, 8, 8, 2
- State at 25 °C
- Solid
- Position
- Group 2, period 4
Proton (+)Neutron (0)Electron (−)
Discovered byHumphry Davy, 1808Humphry Davy: 7 elements
Davy isolated calcium from lime using electricity. Its name comes from the Latin calx, meaning lime.
Did you know?
- It is the most common metal in the human body.
- The Taj Mahal is built from marble, a form of calcium carbonate.
Where it's found
- Limestone, marble and chalk
- Bones, teeth and eggshells
- Milk
What it's used for
- Cement and plaster
- Calcium supplements
- Making steel
Try it
The naked eggSafe at home
- 1Put a raw egg in a glass and cover it with vinegar.
- 2Watch for bubbles, then leave it for 2 days.
- 3Rinse it gently.
What you'll see: The shell dissolves, leaving a bouncy egg held by its membrane. Vinegar reacts with calcium carbonate, giving off carbon dioxide.