The basic units of chemical elements are called atoms. An atom is the smallest unit of matter that retains the properties of an element. Each atom is composed of a nucleus, which contains protons and neutrons, surrounded by a cloud of electrons.
Atoms are unique to each element; for example, a hydrogen atom has one proton and one electron, while a carbon atom has six protons and six electrons. The arrangement and number of these subatomic particles determine the chemical behavior and characteristics of the element. Understanding atoms is fundamental to the study of chemistry, as they form the building blocks for molecules and compounds that make up the various substances in our world.