Chemistry is the science that deals with construction, composition and decomposition of substances. If we want to extract usable elements from minerals or substances to purify and concentrate we need chemistry.

A substance is composed of very small particles. The smallest individual particle is an atom. It looks a bit like a mini - solar system: as planets are in various orbits electrons circling (with a negative charge) around the nucleus which consists of protons (positively charged, their number = atomic number) and neutrons (no charge, count < = protons).

A fabric with only one type of atom is an element. All the elements are arranged in a table (Periodic Table). They are classified into metals and non- metals. Metals are shining, are good conductors of electricity and temperature, and have (except mercury) a high melting point.
An ion is an atom that has one or more electrons given up or added.
Usually, metals have a positive ion, non-metal a negative (e.g. Na+ Cl-). The valence is the charge of an ion type. Which ranges from -2 to 3.

If two atoms have one jointly pair of electrons together, this is called a covalent bond.
Carbon always has 4 covalent bonds, hydrogen 1, oxygen 2.
By binding 2 or more atoms, may result a larger whole: a molecule.
A pure substance consists of only one type of molecules (e.g. water, glucose...). Otherwise it is a mixture.