Calcium (Ca)
Calcium is element 20, a alkaline earth metal in period 4, group 2 of the periodic table. At room temperature it is a solid.
Electron configuration [Ar] 4s2
Electrons per shell 2, 8, 8, 2
Calcium data
| Atomic number | 20 |
|---|---|
| Symbol | Ca |
| Atomic mass | 40.078 u |
| Category | Alkaline earth metal |
| Group | 2 |
| Period | 4 |
| Block | s |
| State at 25 °C | solid |
| Melting point | 1115 K (841.9 °C) |
| Boiling point | 1757 K (1483.9 °C) |
| Density | 1.55 g/cm³ |
| Electronegativity (Pauling) | 1 |
| Atomic radius | 174 pm |
| 1st ionization energy | 590 kJ/mol |
| Electron affinity | -2 kJ/mol |
| Oxidation states | +2 |
| Common ion charge | 2+ |
| Discovered | Known since antiquity |
Orbital diagram
Each box is one orbital holding up to two electrons of opposite spin. Following Hund’s rule, electrons spread out singly across a subshell before pairing.
Work through calcium’s configuration and its ions →
Where calcium sits
Calcium belongs to the alkaline earth metals. Its Pauling electronegativity of 1 is among the lowest on the table, so it gives up electrons readily; see the electronegativity chart and periodic trends for context. To use its mass in a calculation, try the molar mass calculator.
Calcium FAQ
What is the electron configuration of calcium?
Calcium (Z = 20) has the configuration 1s2 2s2 2p6 3s2 3p6 4s2. In noble-gas shorthand that is [Ar] 4s2.
How many valence electrons does calcium have?
2 (outer shell (n = 4)).
What is the atomic mass of calcium?
The standard atomic weight of calcium is 40.078 u, so one mole weighs 40.078 g.
Is calcium a metal?
Yes. Calcium is a alkaline earth metal.
What is the charge of a calcium ion?
Calcium most commonly forms Ca2+.