Polyatomic Ions
Groups of atoms carry a charge together.
About this topic
Polyatomic ions are groups of atoms covalently bonded together carrying an overall charge. Common ones include ammonium (NH4+), hydroxide (OH−), nitrate (NO3−), sulfate (SO4²−), carbonate (CO3²−) and phosphate (PO4³−). They behave as a single unit in reactions and are kept in brackets in formulas when more than one is needed.
Inside the ion atoms are held by covalent bonds, while the ion as a whole forms ionic bonds with oppositely charged ions. Many ions follow the -ate and -ite pattern: sulfate is SO4 2- and sulfite SO3 2-, with one fewer oxygen; adding the prefix per- or hypo- changes it again, as in perchlorate and hypochlorite. Hydrogen-containing versions, such as hydrogen carbonate (bicarbonate), have a lower charge. Memorising the common list saves a lot of time.
For example, aluminium sulfate has Al3+ and SO4 2-, so you need two aluminium and three sulfate to balance: Al2(SO4)3. Polyatomic ions are in fertilisers (nitrates, phosphates, ammonium), cleaning products (hypochlorite), antacids (carbonate and hydroxide) and baking soda.
Common mistakes are leaving out brackets, writing NaOH2 for Na(OH)2 type errors, and thinking the charge belongs to just one atom. The charge belongs to the whole group. Notice also that ammonium is the common positive polyatomic ion.
Key ideas
- Nitrate NO₃⁻, sulfate SO₄²⁻
- Ammonium NH₄⁺
- Memorise the common ones
Quick check
Use cases: where Polyatomic Ions helps
- Homework: review the key idea behind Polyatomic Ions before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Polyatomic Ions without notes.
- Visual learning: play with the interactive lab to see how Polyatomic Ions changes when you adjust its inputs.
- Teaching a friend: explain Polyatomic Ions in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Polyatomic Ions?
Groups of atoms carry a charge together.
What will I learn in Polyatomic Ions?
Nitrate NO₃⁻, sulfate SO₄²⁻. Ammonium NH₄⁺. Memorise the common ones.
Is Polyatomic Ions part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Polyatomic Ions lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Polyatomic Ions?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.