Classical elements typically refer to water, earth, fire, air, and (later) aether, which were proposed to explain the nature and complexity of matter in terms of simpler substances. Ancient cultures in Greece, Tibet, and India had similar lists, sometimes referring in local languages to "air" as "wind" and the fifth element as "void". Modern science doesn’t support the classical elements as the material basis of the physical world. Atomic theory classifies atoms into more than a hundred chemical elements such as oxygen, iron, and mercury. These elements form chemical compounds and mixtures, and under different temperatures and pressures, these substances can adopt different states of matter. The most commonly observed states of solid, liquid, gas, and plasma share many attributes with the classical elements of earth, but these states are due to similar behavior of different types of atoms at similar energy levels, and not due to a certain type of atom or a certain type of substance.

Source: Wikipedia