AQA GCSE Chemistry topic revision

Structure of the atom -
● The atomic number of an atom is the number of protons in an atom.
● The mass number is the number of protons plus neutrons in an atom.
● Atoms have no overall electrical charge, as they contain an equal number
of protons and electrons.
● An ion is a charged atom, so atoms that gain electrons form negative ions,
and atoms that lose electrons form positive ions.
● Isotopes are atoms of the same element but with a different number of
neutrons.
● The relative atomic mass equation is :


● The electrons in an atom occupy the energy levels/shells, and each shell
can occupy max. 8 electrons, excluding the first shell which can only hold
2.




C1 : A
History of the atom -

, Transition elements -
● A transition element can create ions with different charges, form many
coloured compounds and are useful as industrial catalysts.
● Compared to the alkali metals, they have a higher melting point,
stronger, harder, less reactive, don’t react as vigorously




C2 : P
Group 7 (halogens) -

● The elements in group 7 are called the halogens, and are a group of toxic