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Atomic Structure

Anions that contain more than one element
are called Compound Anions.

Below are common compounds that form anions
(negatively charged ions).
NO₃^-,   CO₃^2-,   SO₄^2-,   PO₄^3-.
They are called
nitrate, carbonate, sulfate and phosphate.

In most chemical reactions that you will come across,
compound anions do not split up
but stay as a single species carrying a charge.

For example the Nitrogen and Oxygen in Nitrate (NO₃)
usually stay together as if nitrate is just one thing
(click here for an example).

Examples of ionic compounds that have compound anions are

LiNO₃, Mg(NO₃)₂,   lithium nitrate, magnesium nitrate,           
Na₂CO₃, CaCO₃,    sodium carbonate, calcium carbonate,     
K₂SO₄, MgSO₄,      potassium sulfate, magnesium sulfate,    
 K₃PO₄, Ca₃(PO₄)₂, potassium phosphate, calcium phosphate.

The other common compound anion is hydroxide, (OH)^-.
See acids and alkalis.

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