What is the smallest unit of matter?

The smallest unit of matter is indeed the atom. Atoms are the basic building blocks of all matter and cannot be broken down into smaller parts using standard chemical methods. Each atom consists of a nucleus, which contains protons and neutrons, surrounded by a cloud of electrons. Atoms combine to form molecules and compounds, which are larger structures made up of two or more atoms.

A molecule consists of two or more atoms bonded together, which means it is a larger structure than a single atom. A compound is a type of molecule that includes at least two different elements. An ion refers to an atom or molecule that has a net electrical charge due to the loss or gain of electrons. While these other options are all related to atomic structure and the composition of matter, they are not the fundamental units of matter themselves. Thus, focusing on the definition of an atom is key to understanding why it is recognized as the smallest unit of matter.