How do I determine the number of electrons in an ion with 20 protons and an ionic charge of 2- ?

Remember: Number of protons in an atom = number of eectrons in that atom.

Therefore, in such an atom, there must be 20 electrons. Since this ion has a charge of -2, this means that there are 2 more lectrons in the ion or 2 less protons. But since the number of protons cannot change, there are 2 more electrons. Can you do it now?

If the charge was +2, then, there would have been 2 less electrons.

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