Question

Question #79c23

Answer 1

Polyatomic ions have a charge because they have more or fewer valence electrons than the neutral atoms that make up the ions.

Explanation:

The most common polyatomic cation is the ammonium ion, `"NH"_4^+`.

It has eight valence electrons.

The neutral `"N"` atom originally had 5 valence electron, and each `"H"` atom originally had 1 valence electron, for a total of 9 valence electrons.

The positive charge arises because the 8 negative electrons in `"NH"_4^+` cannot balance the positive charges of the 9 protons in the `"N"` and `"H"` nuclei.

Phosphate ion, `"PO"_4^(3-)`, is a polyatomic anion.

The phosphate ion has 32 valence electrons.

The neutral `"P"` and `"O"` atoms originally had only 5 + 4×6 = 29 valence electrons.

The negative charge is caused by the three extra electrons that came from some outside source, e.g., metal atoms that donated their valence electrons and formed cations.