Every living and non-living component that comprises matter consists of molecules, which are formed from the chemical combination of microscopic particles known as atoms. Unlike atoms, molecules are able to transition from one state of matter into another.
In science, matter is defined as anything that occupies space and has rest mass. The most predominant forms of matter on Earth are categorized into three: solid, liquid and gas. A fourth classification, called plasma, has the biggest proportion of matter in the universe.
A chemical element is a pure substance that cannot be further divided into another type of material by any chemical means or transformation. In the early 17th century, the English chemist John Dalton proposed that chemical elements are made up of distinct atoms that retain all the properties of the element. Atoms fundamentally constitute all known matter. Dalton discovered that atoms have variable masses, which was used as the basis for the laws of definite and multiple proportion. Dalton further suggested that when different types of atoms form chemical bonds, the compound that is created comprises a proportionate number of atoms to its mass. The smallest unit of a compound is referred to as a molecule. One of the most commonly occurring molecules is a water molecule. In its solid form, a water molecule exists as ice, in liquid form as water and in gaseous form as vapor.