What are substances made of only one type of atom called in chemistry?

In chemistry, substances made of only one type of atom are termed elements. Elements are the fundamental building blocks of matter and cannot be broken down into simpler substances through chemical means. Each element is represented by a unique symbol on the periodic table, which categorizes them based on their atomic structure and properties.

For example, hydrogen, oxygen, and gold are all elements that consist solely of one type of atom. This distinguishes them from compounds, which are made of two or more different types of atoms chemically bonded together, and from mixtures, which consist of two or more substances physically combined but not chemically bonded. Molecules refer to groups of two or more atoms bonded together, which can be made up of the same kind of atoms (as in O2, which is molecular oxygen) or different kinds of atoms (as in H2O, which is water). Hence, the designation of substances made up of only one type of atom as elements is critical for understanding the basic structure of matter in chemistry.