Step 3: Calculate the number of electrons in each ion by adjusting for their charges:
- For Cl⁻ (chloride ion), add 1 electron to chlorine's atomic number (17 + 1 = 18 electrons).
- For Ca²⁺ (calcium ion), subtract 2 electrons from calcium's atomic number (20 - 2 = 18 electrons).
- For K⁺ (potassium ion), subtract 1 electron from potassium's atomic number (19 - 1 = 18 electrons).
- For Na⁺ (sodium ion), subtract 1 electron from sodium's atomic number (11 - 1 = 10 electrons).