Calcium (Ca)
Element 20 · alkaline earth metal · group 2, period 4
Calcium is element 20, a alkaline earth metal in group 2 and period 4. Its electron configuration is [Ar] 4s2. That leaves 2 valence electrons in the outer shell, with the shells filling 2, 8, 8, 2. Losing its 2 valence electrons is the shorter route to a full shell, so it carries a charge of +2.
- 20 protons
- 2 valence e−
- +2
- s-block
Calcium Lewis dot structure
Calcium has 2 valence electrons, so its Lewis symbol carries 2 dots: two single dots. The dots go one to a side before any of them pair up, so the unpaired ones show exactly how many bonds the atom tends to form. The ion has given those electrons away, which is why it is drawn in brackets with none.
Draw it in the Lewis structure generator →
Properties
| Atomic number | 20 |
|---|---|
| Symbol | Ca |
| Standard atomic weight | 40.078 u |
| Group | 2 |
| Period | 4 |
| Block | s-block |
| Category | alkaline earth metal |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 |
| Noble-gas notation | [Ar] 4s2 |
| Electrons per shell | 2, 8, 8, 2 |
| Valence electrons | 2 |
| Common ionic charge | +2 |
| Electronegativity (Pauling) | 1 |
| Protons / electrons | 20 / 20 |
Electron configuration of calcium
Orbitals fill from the lowest energy upward. Writing that out for calcium gives 1s2 2s2 2p6 3s2 3p6 4s2, which is 1s2 2s2 2p6 3s2 3p6 4s2 in plain text.
Everything up to Ar is the same as in that noble gas, so it is usually abbreviated to [Ar] 4s2. The part outside the bracket is what does the chemistry.
| Subshell | Electrons | Capacity |
|---|---|---|
| 1s | 2 | 2 |
| 2s | 2 | 2 |
| 2p | 6 | 6 |
| 3s | 2 | 2 |
| 3p | 6 | 6 |
| 4s | 2 | 2 |
Calcium ion charge
Calcium commonly forms ions with a charge of +2.
It has 2 valence electrons, so it is 6 short of a full octet and 2 above an empty outer shell. An atom takes whichever route is shorter, which is why the charge comes out as it does.
Common questions
What is the Lewis dot structure of calcium?
The symbol Ca with 2 dots, one for each valence electron: two single dots. Dots go one to a side before any pair up, the same way electrons fill separate orbitals before sharing one. The Ca2+ ion is drawn in brackets with no dots, because it has lost them.
How many valence electrons does calcium have?
Calcium has 2 valence electrons. For groups 1 and 2 the count is the group number, and calcium is in group 2.
What is the electron configuration of calcium?
1s2 2s2 2p6 3s2 3p6 4s2, or [Ar] 4s2 written from the previous noble gas. Orbitals fill lowest energy first.
What is the charge of calcium?
Calcium commonly forms ions with a charge of +2. With 2 valence electrons it is 6 short of an octet and 2 above an empty shell, so it takes whichever route is shorter.
How many protons, electrons and neutrons does calcium have?
A neutral calcium atom has 20 protons and 20 electrons. Its standard atomic weight is 40.078, so the most common isotope has about 20 neutrons.
Nearby elements
See the ionic charge of every element →