Elements consist of a single type of atom. 

Elements are the fundamental building blocks of matter. They are pure substances that cannot be broken down into simpler substances by ordinary chemical means. Each element is defined by the specific number of protons in its atoms, known as the atomic number. Crucially, all atoms of a given element have the same number of protons. For example, all gold atoms have 79 protons, making them gold. While atoms of the same element can have different numbers of neutrons (isotopes), they must have the same number of protons to be considered the same element. This uniformity in atomic composition is what distinguishes elements from compounds and mixtures.