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GCSE Chemistry · key term
A pure substance made from only one type of atom.
Used by AQA, Edexcel and OCR
Specification 4.1.1.1 · Paper 1, Paper 2
Revise: Atoms, Elements and the Periodic TableAn atom is the smallest part of an element that can exist. For example, an oxygen atom is the smallest unit that is still oxygen. Atoms contain smaller particles, but an isolated proton or electron is not an atom of oxygen—or an atom of any other element.
A pure substance made from atoms that all have the same number of protons.
Specification 1.8, 1.16, 1.17, 2.5 · Paper 1, Paper 2
A pure substance whose atoms all contain the same number of protons in their nuclei.
Revise: Atoms and ProtonsOf these particles, it is the number of protons in the nucleus that determines which element the atom belongs to.
A substance whose atoms all have the same number of protons.
A substance made from only one type of atom, identified by its unique atomic number.
A substance made from only one type of atom; it may contain single atoms or molecules of that element.
Specification C2.1a, C2.2b · Paper 1 (Foundation), Paper 3 (Higher)
A substance made from only one type of atom.
Revise: Defining PurityA pure compound can contain more than one element. For example, water contains hydrogen and oxygen atoms chemically bonded together, but a sample containing water and no other substance is still pure.
A substance containing only one type of atom, identified by its number of protons.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
Revise: Purity definitionA pure substance contains only one element or only one compound. There are no other substances mixed with it.
You will be given a periodic table in the exam. Use the atomic numbers to locate elements rather than relying only on the table’s shape.
When writing an electronic structure, check that its numbers add up to the atom's atomic number. For the first 20 elements, fill the shells in the pattern 2,8,8,2.
Do not apply the simple 2,8,8 filling method to every element: it is the model used here for the first 20 elements, and transition elements make the later pattern more complicated.
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