All substances, both living and non-living, are composed of matter
The fundamental unit of matter is the atom, which consists of:
- Protons (+ve charge) and neutrons (no charge) within a central nucleus
- Electrons (–ve charge) circling the nucleus in regions called orbitals
Different atoms will possess different chemical properties (how they react)
Atoms can be grouped by properties and displayed according to a periodic table
Periodic Table of Elements
Atoms in the same group (columns) share chemical properties as they have the same number of electrons in their outer shell
Atoms in the same period (rows) have the same number of electron shells but do not share any consistent chemical properties
Atoms always have the same number of protons and electrons - when they gain or lose electrons they become charged ions
An atom may have a different number of neutrons - these different forms are called isotopes and can cause radioactive decay