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

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:

and the electron configuration (Ca²⁺ ) becomes:

1s², 2s², 2p⁶, 3s², 3p⁶

periodic trends is an atom that gets larger as the number of electronic shells increase, the radius of atoms increases as you go down a certain group in the periodic table of elements. in general, the size of an atom will decrease as you move from left to right of a certain period.