Matter can be classified into elements, compounds and mixtures.
An element is a substance, which cannot be split into two or more simple forms by any known chemical process. It can also mean a substance which cannot be decomposed into a simpler substance by ordinary chemical means.
There are 109 known elements, 90 occur naturally while the rest are artificial. Elements can be grouped in the periodic table as reactive elements, transition elements, lanthanide, actinide, pure metals, non-metals and rare (noble) gases.