Cation first, anion second

The idea

An ionic compound is named by writing the name of the cation first, followed by the name of the anion; names of simple anions end in -ide.

Reading a name

Common salt is called sodium chloride. Calcium oxide and magnesium sulfide are also ionic compounds.

Look at these names. Which ion do you think is named first?

• The positive ion, the cation
• The negative ion, the anion
• Whichever has more atoms

Build a name

Choose a cation and an anion and read the name of the compound.

The naming rule

The name of the cation is written first and the name of the anion second. A simple anion's name ends in -ide: chloride, oxide, sulfide.

An ionic compound is named by writing the name of the cation first, followed by the name of the anion. Names of simple anions end in -ide.

Notes

Name the cation first, then the anion. Simple anions end in -ide: sodium chloride, calcium oxide, magnesium sulfide.

Check yourself

Which is the correct name of the compound of Na⁺ and Cl⁻?

In the name of an ionic compound, which part is written first?

What is the name of the compound made of Mg²⁺ and S²⁻ ions?

What ending do the names of simple anions have?

• Chloride sodium. The cation is named first, then the anion.
• Sodium chloride — correct. Yes!
• Sodium chlorine. The simple anion's name ends in -ide, so it is chloride.
• The name of the anion. The cation's name comes first, followed by the anion's name.
• The name of the heavier ion. The order depends on charge, not on mass. The cation is named first.
• The name of the cation — correct. Yes!
• Magnesium sulfide — correct. Yes!
• Sulfide magnesium. The cation, magnesium, is named first.
• Magnesium sulfate. Sulfate is a different ion, SO₄²⁻. The simple anion S²⁻ is called sulfide.
• -ium. Names such as sodium, calcium and potassium are names of cations, not of simple anions.
• -ide — correct. Yes!
• -ate. Names such as sulfate and nitrate are names of polyatomic ions. Simple anions end in -ide.