Question

How many electrons would be in a calcium cation with a positive 2 charge?

Answer 1

Number of electrons in a Ca²⁺ = 18

Further explanation  

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:

$\tt 20-2 = 18$

and the electron configuration (Ca²⁺ ) becomes:

1s², 2s², 2p⁶, 3s², 3p⁶