Classifying Matter by Composition

Matter is made of atoms, the smallest basic units of matter, and molecules, which are formed by combining two or more atoms together. Based on its composition, matter can be classified into two groups — pure substances and mixtures.

By definition, a matter is said to be pure if it is made of only one component, with a uniform composition throughout. For example, take helium. Helium is made up of only helium atoms. Similarly, water is made of only water molecules. These compositions do not vary from sample to sample. 

Pure substances can be categorized into two types, elements and compounds, depending on whether or not they can be broken down. 

Elements are pure substances that cannot be broken down into simpler substances by chemical means. For example, helium is an element.

Compounds, on the contrary, are substances that can be separated into their constituents only by chemical means. For example, water, also a pure substance, can be chemically broken down into two simpler substances, hydrogen and oxygen, meaning it is a compound. 

On Earth, compounds are more common than pure elements because most elements will readily combine with other elements. For example, chalk used for writ