Number of electrons in a Ca²⁺ = 18
In an atom there are levels of energy in the shell and sub shell
This energy level is expressed in the form of electron configurations.
Writing electron configurations starts from the lowest to the highest sub-shell energy level. There are 4 sub-shells in the shell of an atom, namely s, p, d and f. The maximum number of electrons for each sub shell is
• s: 2 electrons
• p: 6 electrons
• d: 10 electrons and
• f: 14 electrons
Charging electrons in the sub shell uses the following sequence:
1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁶, 5s², 4d¹⁰, 5p⁶, 6s², etc.
The element Ca has an atomic number of 20, so the number of electrons and protons (in neutral atoms) is also 20
Electron configuration of Ca : 1s², 2s², 2p⁶, 3s², 3p⁶, 4s² ⇒[Ar] 4s²
When Ca releases 2 electrons to gain stability (forming Ca²⁺ cations), the number of electrons becomes:
[tex]\tt 20-2 = 18[/tex]
and the electron configuration (Ca²⁺ ) becomes:
1s², 2s², 2p⁶, 3s², 3p⁶
