Atoms, Elements and Compounds
Atoms, elements and compounds is the topic covering the structure of the atom and how atoms combine to form the substances around us. It introduces subatomic particles, atomic number and mass number, the periodic table's groups and periods, relative formula mass, and the difference between elements, compounds and mixtures.
Method
- Learn the three subatomic particles, their relative charges and relative masses, and where each is found in the atom.
- Use atomic number and mass number to work out the number of protons, neutrons and electrons in an atom.
- Classify substances as elements, compounds or mixtures from their formula or description.
- Learn how the periodic table is arranged into groups and periods, and what these tell you about an atom.
- Practise writing and balancing simple symbol equations, checking atoms of each element balance on both sides.
- Learn the separation techniques (filtration, evaporation, distillation, chromatography) and match each to the property it relies on.
Worked example
Calculate the relative formula mass (Mr) of magnesium oxide, MgO. Use these Ar values: Mg = 24, O = 16.
- Identify the atoms present in the formula: 1 magnesium atom and 1 oxygen atom.
- Write down the Ar value for each atom: Mg = 24, O = 16.
- Add the Ar values together: 24 + 16.
- Calculate: 24 + 16 = 40.
- State the final answer: Mr(MgO) = 40.
Practice questions
Type your answer and press Check to be marked straight away, or reveal the answer and mark yourself.
Q1Which subatomic particle has a relative charge of +1?Show answer
Answer: Proton
Q2State where electrons are found in an atom.Show answer
Answer: In shells (energy levels) surrounding the nucleus.
Q3Classify sea water as an element, compound or mixture.Show answer
Answer: Mixture
Q4An atom has atomic number 8 and mass number 16. Calculate the number of neutrons.Show answer
Answer: 8 (16 - 8 = 8)
Q5Calculate the relative formula mass (Mr) of carbon dioxide, CO2. Use Ar: C = 12, O = 16.Show answer
Answer: 44 (12 + 16 + 16)
Q6Balance this symbol equation by writing in the missing numbers: ___Fe + ___O2 -> ___Fe2O3Show answer
Answer: 4Fe + 3O2 -> 2Fe2O3
Exam-style questions
Written in the style of a KS3 Science exam paper, with a full mark scheme.
An atom of potassium has atomic number 19 and mass number 39. State the number of protons, electrons and neutrons in this atom.
Show mark scheme
Tick each line you got. Your score builds from the marks on the scheme.
Nothing ticked yet - 3 available
A student has a mixture of iron filings and sulfur powder. Describe a method, using a magnet, that she could use to separate the iron filings from the sulfur, and explain why this method works.
Show mark scheme
Tick each line you got. Your score builds from the marks on the scheme.
Nothing ticked yet - 4 available
A rock salt sample contains 24.0 g of salt mixed with 16.0 g of sand (40.0 g total mixture). A student dissolves the salt in water, filters off the sand, then evaporates the filtrate to recover 21.6 g of dry salt crystals, and separately dries and weighs 15.0 g of sand. Calculate the percentage of the original salt that was recovered as dry crystals, calculate the total mass of solid recovered, and explain why it is less than the original 40.0 g.
Show mark scheme
Tick each line you got. Your score builds from the marks on the scheme.
Nothing ticked yet - 5 available
Free printable worksheet
Want more practice on paper? Download the atoms, elements and compounds worksheet pack - 14 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
Next topics
Not quite what you needed?
Tell us what is missing on atoms, elements and compounds, or which topic to write up next. Every request is read, and we reply to every one.
Build a full practice pack.
This topic is one of hundreds in the library - pick the ones a student needs and generate a printable PDF in minutes.