What defines an element compared to a compound?

An element is a pure substance made of one type of atom, while a compound is a substance made of two or more different atoms.

An element is the simplest form of matter that cannot be broken down into simpler substances by ordinary chemical means. It is composed of atoms of the same type, each with the same number of protons in the nucleus. This number, known as the atomic number, defines the element. For example, all atoms with one proton are hydrogen, all atoms with two protons are helium, and so on. Elements can exist in different forms, or allotropes, such as carbon existing as graphite, diamond, or fullerene, but these are still the same element because they contain only carbon atoms.

On the other hand, a compound is a substance that is made up of two or more different elements that are chemically combined. The atoms in a compound are held together by chemical bonds, which can be either ionic (formed by the transfer of electrons) or covalent (formed by the sharing of electrons). The properties of a compound are usually different from the properties of the elements it contains. For example, sodium is a highly reactive metal and chlorine is a poisonous gas, but when they combine to form sodium chloride, the result is common table salt, which is safe to eat.

In summary, the key difference between an element and a compound is that an element is a pure substance made of one type of atom, while a compound is a substance made of two or more different atoms that are chemically combined. Understanding this distinction is fundamental to the study of chemistry.