Metals are classified into three main categories.
- Very reactive metals: These are metals which usually occur naturally in the combined state.
These include metals which occupy the upper position of the electrochemical (activity) series like potassium, sodium, calcium, aluminum and zinc. They can therefore be extracted by Electrolysis of their molten or fused salts.
- Less reactive metals: These include metals which occur naturally in the form of carbonates, oxides and sulphides, They occupy the middle position in the activity series and can be extracted by chemical reduction. Examples include iron and lead.
- Least reactive metals: These are metals which occupy the lower position in the activity series. They can be extracted by thermal reduction.
Examples include copper, mercury, silver and gold.