Elements
The term “element” was first referred to as stoicheia by Plato, the Greek philosopher in 360 BCE in his dialogue on speculation of the physical world. This dialogue has been termed as Timaeus. The literal meaning of the term stoicheia is “letter of the alphabet”, a basic unit of a word. Plato used these elements in reference to air, fire, water and earth along with their properties of hot, cold, dry and wet. These elements were first created by Empedocles in 450 BC who called these elements as roots. To these four elements Aristotle added up a fifth one called the “aether” or “quintessence” derived from the word quint meaning fifth. Aristotle suggested that while there were no changes seen in the heavenly regions it clearly indicates that stars are made up of a heavenly substance that is unchangeable unlike the other four earthly, changeable elements.
An element is a pure chemical substance that contains atoms with an equal number of protons. In all there have been 117 elements observed to date of which 94 are the naturally occurring ones. Those elements with atomic numbers greater than 82 are unstable and undergo radioactive decay thereby loosing energy by emitting radiation.
