Atomic structure and the periodic table: GCSE Chemistry
Atoms, elements, compounds, mixtures, the nuclear model, relative masses and Groups 1, 7 and 0
The short version
Atoms have a nucleus of protons and neutrons, with electrons in shells. The periodic table orders elements by proton number. Groups share similar reactions.
Key idea
O2 is a molecule of an element, not a compound
Grade 2–3: Gold is an element. Water is a compound because it is hydrogen and oxygen joined.
Grade 5–6: I write chemically combined in a fixed ratio. H2O means 2 H and 1 O. Air is a mixture, not a compound.
Grade 9: I balance CH4 + 2O2 → CO2 + 2H2O by changing only the big numbers. I never change H2O into HO to make the counts easier.
Go a bit deeper
A word equation names reactants and products. A symbol equation uses formulae and must be balanced: the same number of each atom on both sides. Fe + O2 → Fe2O3 becomes 4Fe + 3O2 → 2Fe2O3.
Worked example
Worked example
Grade 2–3: Gold is an element. Water is a compound because it is hydrogen and oxygen joined. Grade 5–6: I write chemically combined in a fixed ratio. H2O means 2 H and 1 O. Air is a mixture, not a compound. Grade 9: I balance CH4 + 2O2 → CO2 + 2H2O by changing only the big numbers. I never change H2O into HO to make the counts easier.
Lessons in this topic
- Atoms, elements and compounds
- Mixtures
- The model of the atom
- Relative masses and moles intro
- The periodic table
- Groups 1, 7 and 0
In the app each lesson is video (when we have a real YouTube id) then intro, learn and summary steps.
What the examiner wants
State: atoms of an element have the same proton number. Compounds are two or more elements chemically combined in a fixed ratio. Use A_r as a weighted mean of isotope masses.
Try these questions
Cover the answers and have a go first. Worked solutions are underneath.
Which statement about a compound is correct?
O₂ is best described as
Which method separates sand from salt water after stirring?
Simple distillation is used to
Common mistakes
- O2 is not a compound. Compounds include H2O, CO2 and NaCl. Never change a formula to balance an equation.
- Boiling a solution dry often gives a powder, not well-formed crystals, and can decompose the salt. Chromatography has its own required practical in Chemical analysis.
- Mass number is the top number. Students swap A and Z. Every atom has a nucleus — plum pudding was rejected because some alpha particles bounced back.
- Brackets: Mg(NO3)2 has two nitrate groups, not one. A_r is not always a whole number because of isotopes, not because electrons weigh 0.5.
Answers and working
Frequently asked questions
Is GCSE Atomic structure and the periodic table on Combined Science and Triple?
Atomic structure and the periodic table is on Combined Science and on Triple Chemistry. Progress is shared in the ReviseEasy app.
Which exam board is this Atomic structure and the periodic table page for?
The ideas are board-agnostic for AQA, Edexcel, OCR, WJEC and CCEA. Paper lengths and question numbers differ — check your specification.
Is Atomic structure and the periodic table Foundation or Higher?
The core ideas appear on both tiers. Higher papers add extra application and some HT-only detail, marked in lessons with a Higher badge.
Learn, try, get feedback, fix the mistake
Open the stepped lesson, then the quiz with hints. Required-practical and calculation questions use the same method you will need in the paper.
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