What is defined as a substance that cannot be broken down into another substance?

An element is defined as a substance that cannot be broken down into simpler substances through chemical means. Elements are the fundamental building blocks of matter and consist of only one type of atom. For example, elements like oxygen, carbon, and gold cannot be separated into different substances while retaining their chemical properties.

In contrast, compounds are substances formed when two or more elements chemically combine in a fixed ratio. Molecules are groups of atoms bonded together, which can include multiple elements or the same element. Mixtures consist of two or more substances that are physically combined but not chemically bonded, meaning they can be separated without breaking chemical bonds. Understanding these distinctions helps clarify the unique role elements play in the study of chemistry and the composition of matter.