Cambridge IGCSE Chemistry · Syllabus 0620 · Atoms, Elements and Compounds
Element
What is Element?
A substance that contains only one type of atom, meaning every atom in it has the same proton number. An element cannot be broken down into simpler substances by chemical means. Its atoms may exist separately, as in argon, joined in molecules, as in oxygen, or joined in a giant structure, as in diamond, and in every one of those cases the substance is still an element.
This definition is part of the Atoms, Elements and Compounds chapter in Cambridge IGCSE Chemistry.
Common mistakes with Element
- 1. “An element is a substance made of single, separate atoms.” Core 2.1.1 Repair An element contains only one type of atom. Those atoms may be separate (argon), joined in molecules (\(\mathrm{O_2}\), \(\mathrm{S_8}\)) or joined in a giant structure (diamond). It is still an element. Taught fully in Lesson 2.1.
- 2. “Mass number and relative atomic mass are the same thing.” Supplement 2.3.4 Repair Mass number belongs to one atom and is always a whole number. Relative atomic mass belongs to the element and is an abundance-weighted mean, so it is usually not a whole number. Taught fully in Lesson 2.3B, which is a Supplement — Extended candidates section. Core candidates still need to know that the two quantities are different (mass number is Core 2.2.4); only the calculation is Supplement.
- 3. “An ion forms when an atom gains or loses protons.” Core 2.4.1 Repair Only electrons move. The nucleus is untouched, so the proton number — and therefore the element — never changes when an ion forms. Taught fully in Lesson 2.4A.
- 4. “Change the number of neutrons and you get a different element.” Core 2.3.1 Repair You get a different isotope of the same element. Identity is set by the proton number alone. Taught fully in Lesson 2.3A.