Atoms, elements, compounds and reactions
Clear notes with worked examples, then 4 practice questions with answers. Written by Beyond Tutors tutors for the KS3 National Curriculum.
Atoms and elements
Everything is made of atoms. An element contains only one type of atom (iron, oxygen, carbon).
The periodic table lists all the elements. Metals: left and middle. Non-metals: right.
Elements in the same GROUP (column) react in similar ways.
Compounds
Two or more elements chemically joined. Water : 2 hydrogen + 1 oxygen.
Carbon dioxide : 1 carbon + 2 oxygen.
MIXTURE vs COMPOUND
Mixture: not joined, easy to separate (air, salt water).
Compound: chemically joined, new properties (water, salt).
Chemical reactions
reactants → products
magnesium + oxygen → magnesium oxide
Mass is conserved: atoms are rearranged, never created or destroyed.
Signs of a reaction
gas given off, colour change, temperature change, new solid (precipitate) forms
Practice questions
Try each one, then tap to see the answer and why.
- Question 1 · Periodic table
Elements in the same group of the periodic table ...
- Ahave similar chemical properties
- Bhave the same mass
- Care all gases
- Dwere discovered at the same time
Show the answer
A: have similar chemical properties
Elements in a group react in similar ways, e.g. the alkali metals.
- Question 2 · Periodic table
Where are the metals found on the periodic table?
- AOn the right
- BOnly at the bottom
- COnly at the top
- DOn the left and in the middle
Show the answer
D: On the left and in the middle
Metals are on the left and centre; non-metals are on the right.
- Question 3 · Chemical reactions
Magnesium burns in oxygen. What is the product?
- AMagnesium oxide
- BMagnesium oxygenate
- CMagnesium carbonate
- DOxygen magnesium
Show the answer
A: Magnesium oxide
Magnesium + oxygen → magnesium oxide.
- Question 4 · Atoms and elements
What is an element?
- AA mixture of atoms
- BA substance made of only one type of atom
- CTwo atoms bonded together
- DA liquid
Show the answer
B: A substance made of only one type of atom
An element contains only one type of atom, e.g. oxygen or iron.