Elements are a form of matter that can not be broken down by ordinary chemical or physical means. Each element is represented on the periodic table of elements by its own symbol. Currently, 112 elements are known to exist although only 92 of these occur in nature. The other 20 are known as transuranium elements and have only been produced artificially. While elements were once thought to be irreducible, they have since been found to be composed of subatomic particles.

The idea that matter was made up of elements was first proposed by ancient Greek philosophers. Many of these early scholars believed that nature was not fundamentally complex, but was instead made up of a small number of basic materials. These ideas eventually led to a proposal by Empedocles (c. 490-430 B.C.) in the fifth century B.C. that all matter was based on four elements: earth, air, fire, and...