What is an element?

An element is a `pure substance` consisting of atoms of the same kind. Elements cannot be broken down into simpler substances, but they can combine with other elements to make new substance. Each element  has a unique symbol, for example, `O` means oxygen, `Na` means sodium (Latin: naturium),and `Cl` means chlorine. The number of protons in the atomic nucleus determines the element. The number is called the atomic number of the element.