A Level Chemistry - AQA - Periodicity - Summary Notes

Unit 2 – Periodicity
Periodicity

 The Periodic Table provides chemists with a structured
organisation of the known chemical elements from which
they can make sense of their physical and chemical
properties.
 The historical development of the Periodic Table and
models of atomic structure provide good examples of how
scientific ideas and explanations develop over time.

The Periodic Table arranges elements by proton number:

The periodic table is arranged into periods and groups by
atomic number.

- All of the elements within a period have the same number of
electron shells.
E.g In Period 2 they have 2 electrons in their outer shell.

- All of the elements within a group have the same number of
electrons in the outer shell.
E.g Group 1 elements have 1 electron in their outer shell.

The exception is Group 0 however, which all have full outer
shells. There is 2 electrons for Helium and 8 electrons for the
others.

You can use the periodic table to work out electron
configurations:

An element is classified as
s block, p block, d
block or f block
according to its position
in the Periodic
Table, which is
determined by its proton
number.