AQA Chemistry (8462) 4.1.1.1 · Classify
Atoms, elements and compounds
Every substance is atoms. So what makes one substance an element, another a compound and a third a mixture, and how can you tell from a drawing of its particles?
Triple Science · Foundation tier
Start here
A metal that burns, a gas that poisons, a crystal you eat.
Sodium is a soft metal that reacts violently with water. Chlorine is a toxic yellow-green gas. Bring the two together and you get sodium chloride: table salt, safe to sprinkle on food.
If you had to guess, are the sodium and chlorine in salt just mixed together, or joined up into something new?
All substances are made of atoms. An atom is the smallest part of an element that can exist. An element contains only one type of atom. There are about 100 elements (118 are known today), each with a symbol in the periodic table: C is carbon, Fe is iron, Na is sodium.
A compound forms when two or more elements react and become chemically combined in fixed proportions. It is a new substance with different properties, and only a chemical reaction can separate it into its elements. A mixture is two or more elements or compounds not chemically combined: each keeps its chemical properties, the proportions can vary, and physical processes such as filtration or distillation separate it.
Zoom in
Call each box of particles before it is named.
0 of 6 called
Commit first. Is box 1 an element, a compound or a mixture?
Sort it
Element, compound or mixture?
Ten substances, named but not drawn. Decide from the name or formula.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Every compound has a formula. The small number after a symbol counts the atoms of that element only: H₂SO₄ has 2 hydrogen, 1 sulfur and 4 oxygen atoms. A symbol equation shows reactants turning into products. Atoms are not created or destroyed in a reaction, only rearranged, so the equation must be balanced: the same number of each type of atom on both sides. Written as H₂ + O₂ → H₂O, hydrogen + oxygen → water is not balanced: 2 O on the left, 1 on the right.
Think again
“H₂ + O₂ → H₂O has one oxygen too few on the right, so I will write the water as H₂O₂.”
Spot the flaw
ExplainWhat is wrong with that fix?
Balance it · numbers in front only
Watch one balanced. Then balance three yourself.
0 of 3 balanced
Worked · hydrogen + oxygen → water
magnesium + oxygen → magnesium oxide
Command words in this lesson
- Identify
- Pick out the answer from what you are shown: a particle diagram, a formula or a list.
- Give
- Only the answer is needed, not an explanation.
- Complete
- Write the missing parts in the spaces: here, the numbers that balance an equation.
- Explain
- Give the reason: chemically combined or not, fixed proportions or not, chemical or physical separation.
Key fact
Reading a particle diagram: an element has only one type of atom. A compound has atoms of two or more elements chemically combined in the same fixed ratio throughout. A mixture has two or more different substances that are not chemically combined with each other.
Key note · AQA 4.1.1.1
Atoms, elements and compounds
Photograph this card. Tomorrow, cover it and say each line first.
Previous and next
Connects to
Ask MrBadmus
Not sure whether a substance is an element, a compound or a mixture?
The particle boxes are flat models: real atoms have no colours or letters, and a real gas is far more spread out than drawn. In the mixture boxes the substances slide apart to show they are not chemically combined; a real separation needs a physical process such as filtration or distillation. The iron sulfide and bronze boxes show one layer of a giant structure.