Calculate the number of electrons for each ion by adjusting the number of electrons in the neutral atom by the charge of the ion:
- For Ca^{2+}, subtract 2 electrons from calcium's atomic number (20).
- For Na^{+}, subtract 1 electron from sodium's atomic number (11).
- For K^{+}, subtract 1 electron from potassium's atomic number (19).
- For Cl^{-}, add 1 electron to chlorine's atomic number (17).