Calcium (Ca): electron configuration, atomic mass and facts
Calcium (Ca) is element 20 of the periodic table, an alkaline earth metal in period 4, group 2. Its electron configuration is [Ar] 4s2, with electrons arranged in shells 2, 8, 8, 2, and its standard atomic weight is 40.078 u.
💡 Builds bones and teeth. Its compounds give a brick-red flame.
▶ Watch Calcium’s electrons orbit in the interactive periodic tableCalcium at a glance
| Symbol | Ca |
|---|---|
| Atomic number | 20 |
| Atomic mass | 40.078 u |
| Category | Alkaline earth metal |
| Group | 2 |
| Period | 4 |
| Block | s-block |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 |
| Noble-gas shorthand | [Ar] 4s2 |
| Electrons per shell | 2, 8, 8, 2 |
| Outer-shell electrons | 2 |
| Electronegativity (Pauling) | 1 |
| State at 20 °C | solid |
| Flame test colour | brick red |
Experiments with calcium
🫧 CO₂ and limewater
Marble + acid makes CO₂. Bubble it through limewater: milky, then clear again in excess.
🧊 Hot & cold packs
Dissolving salts can absorb heat (NH₄NO₃) or release it (CaCl₂, NaOH).
Where is Calcium on the periodic table?
Calcium is in period 4, group 2, in the s-block. The period number matches its 4 electron shells, and the block names the subshell its last electrons fill. In the same group, Magnesium sits directly above it and Strontium sits directly below it. Elements in one group have the same number of outer-shell electrons (2 here), which is why they react in similar ways.
How to work out the electron configuration of Calcium
Put 20 electrons into subshells in order of rising energy, filling each before starting the next: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁶ (18), 4s² (20). In shorthand, [Ar] stands for the 18 electrons of argon, giving [Ar] 4s².
How electronegative is Calcium?
Calcium has a Pauling electronegativity of 1, ranking 91 of the 100 elements with a known value (fluorine is highest at 3.98). That is low: it tends to give up electrons and form positive ions.
Calcium in the virtual lab
Faradium’s chemistry workbench includes these chemicals that contain calcium: Calcium granules, Marble chips, Quicklime, Slaked lime, Calcium chloride, Limewater. Open the Chemistry Lab to experiment with them.
Frequently asked questions
What is the electron configuration of Calcium?
The electron configuration of Calcium (Ca) is 1s2 2s2 2p6 3s2 3p6 4s2. In noble-gas shorthand it is written [Ar] 4s2.
How many electrons does Calcium have in each shell?
Calcium has 20 electrons arranged in shells as 2, 8, 8, 2. It has 2 electrons in its outer shell.
What is the atomic mass of Calcium?
The standard atomic weight of Calcium is 40.078 u, so one mole of Calcium atoms has a mass of about 40.078 g.
Is Calcium a metal?
Yes. Calcium is an alkaline earth metal.
Explore nearby elements
More alkaline earth metals: Beryllium, Magnesium, Strontium, Barium, Radium. See all elements on the periodic table.