What term describes a pure chemical substance made up of only one type of atom?

The term that describes a pure chemical substance made up of only one type of atom is "element." Elements are the fundamental building blocks of matter and cannot be broken down into simpler substances by chemical means. Each element is defined by the number of protons in its atomic nucleus, which is unique to that particular type of atom.

For example, oxygen is an element consisting entirely of oxygen atoms, and gold is composed solely of gold atoms. Elements are listed in the periodic table, where each entry represents a different type of atom.

In contrast, a compound consists of two or more different elements that are chemically bonded together, forming a new substance with properties different from those of the individual elements. A solution involves a homogenous mixture of substances, often a solute dissolved in a solvent, while a mixture is a combination of two or more substances that retain their individual properties and can be separated by physical means. These distinctions emphasize the uniqueness of elements as pure substances comprised of a single type of atom.