Question #79c23

1 Answer
Feb 11, 2014

Answer:

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.

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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.

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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.