AQA Chemistry (8462) 4.2.1.1 · Classify
Chemical bonds
Name two elements. Can you say how they will bond, and what the substance will do, before you ever see it?
Triple Science · Higher tier
Start here
Same chlorine. Two partners. Two different worlds.
Sodium is a soft metal that fizzes on water. Chlorine is a poisonous green gas. Together they make table salt: a white crystal that stays solid until 801 °C. Swap sodium for hydrogen and chlorine makes hydrogen chloride, which stays a gas until it is cooled below −85 °C.
Commit first
What decides whether chlorine ends up in a high-melting crystal or in a gas?
Atoms bond because a full outer shell is more stable, and there are only three ways to get one. Most metal atoms have one, two or three outer electrons and give them away. Most non-metal atoms have four to seven and take more in, or share.
Metal with non-metal: electrons are transferred, the atoms become oppositely charged ions, and the ions attract. That is ionic bonding. Two non-metals: neither gives way, so they share pairs of electrons. That is covalent bonding. Metal atoms on their own release their outer electrons into a sea that belongs to the whole lump. That is metallic bonding. So the first question is always the same: metal or non-metal?
The bond decider
Pick two elements. Call the bond. Watch it form.
0 pairs called
Tap an element, then its partner. Tap the same element twice for the element on its own.
Part of the periodic table, by group. Most transition metals and Group 3 are left out.
No pair yet
The bond decides what the substance does. Ionic compounds and metals are giant structures, held by strong attraction all the way through, so most melt only when very hot. Covalent substances split two ways. Most are small molecules that melt and boil at low temperatures; a few, like diamond and sand, are giant networks that melt only when very hot. To carry a current you need charged particles that can move: a metal's electron sea always can, but ions only can once the solid melts or dissolves.
Think again
“Ice melts at 0 °C and salt at 801 °C, so the covalent bonds in water must be weak.”
Spot the flaw
ExplainWhat is wrong with that reasoning?
Sort it
Ionic, covalent or metallic?
Eight substances. Decide from the elements in each, not from what you remember about it.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Command words in this lesson
- Identify
- Name it. One word or a short phrase is enough.
- Predict
- Give a likely outcome. Here, say which elements are metals.
- Deduce
- Reach a conclusion from the data you are given.
- Justify
- Back your answer with evidence from the question.
Key fact
Metal with non-metal: ionic, electrons transferred. Non-metal with non-metal: covalent, electrons shared. Metal on its own or with other metals: metallic, electrons delocalised.
Examiner tip
Key note · AQA 4.2.1.1 (8462)
Chemical bonds
- Atoms bond to reach a full outer shell, like a noble gas.
- Metal + non-metal: ionic. The metal transfers electrons; the ions attract.
- Non-metal + non-metal: covalent. The atoms share pairs of electrons.
- Metal alone or in an alloy: metallic. Positive ions in a sea of delocalised electrons.
- Hydrogen is a non-metal, even though it has one outer electron like Group 1.
- Justify every prediction from the elements: say which ones are metals.
Photograph this card. Tomorrow, cover it and say each line first.
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Ask Mr Badmus AI
Stuck on an element that does not fit the rule?
The decider uses the GCSE rule: metal with non-metal is ionic, two non-metals are covalent, metals are metallic. Real bonding is a sliding scale and a few metal compounds, such as aluminium chloride, behave covalently; GCSE questions avoid them. Dot-and-cross figures show outer shells only for covalent molecules and full shells for ions.