Ions made of several atoms
Polyatomic ions.
A group that carries one charge
Some ions are not single atoms. The sulfate ion, SO₄²⁻, has one sulfur atom and four oxygen atoms together, with a charge of 2−.
What do you think such an ion is called?
What this lesson covers
The idea
Ions formed by the combination of atoms of two or more elements are polyatomic ions; unlike simple anions, their names generally lack the -ide ending.
A group that carries one charge
Some ions are not single atoms. The sulfate ion, SO₄²⁻, has one sulfur atom and four oxygen atoms together, with a charge of 2−.
What do you think such an ion is called?
- A polyatomic ion
- A monoatomic ion
- A molecule
What is it made of?
Match each polyatomic ion with the atoms in it.
Polyatomic ions
An ion made of atoms of two or more elements is a polyatomic ion. Most of their names do not end in -ide: sulfate, nitrate, carbonate, ammonium. The simple anions chloride, oxide and sulfide do end in -ide.
Ions formed by the combination of atoms of two or more elements are polyatomic ions. Unlike simple anions, their names generally lack the -ide ending.
- Name of ion | Formula | Valency
- Hydroxide | OH⁻ | 1
- Nitrate | NO₃⁻ | 1
- Hydrogencarbonate | HCO₃⁻ | 1
- Carbonate | CO₃²⁻ | 2
- Sulfate | SO₄²⁻ | 2
- Ammonium | NH₄⁺ | 1
Notes
Polyatomic ions are ions of two or more elements combined, such as SO₄²⁻ and NO₃⁻. Their names generally lack -ide.
Check yourself
Which of these is a polyatomic ion?
How many atoms are there in one ammonium ion, NH₄⁺?
Answer: 5
One nitrogen atom and four hydrogen atoms make 5 atoms.
Which name belongs to a polyatomic ion?
How are polyatomic ions formed?
- Chloride, Cl⁻. Chloride is a simple ion made of one kind of atom, chlorine.
- Nitrate, NO₃⁻ — correct. Yes!
- Sodium, Na⁺. Sodium is a simple ion made of one kind of atom, sodium.
- Oxide. Oxide, O²⁻, is a simple anion. Simple anions end in -ide.
- Sulfide. Sulfide, S²⁻, is a simple anion. Simple anions end in -ide.
- Sulfate — correct. Yes!
- By atoms of two or more elements combining — correct. Yes!
- By a single atom losing one electron. An ion from a single atom is a simple ion, not a polyatomic one.
- By a molecule splitting into atoms. A polyatomic ion is formed when atoms of two or more elements combine, and it carries a charge.