A chemical element is a species of atom having the same number of protons in its atomic nuclei. There are 118 known elements, of which 94 are known to occur naturally on Earth. The number of protons in an atom's nucleus is known as its atomic number, and it is this number that defines the element. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon, and all atoms with 92 protons in their nuclei are atoms of the element uranium.
The concept of an element dates back to ancient times, when philosophers such as Empedocles and Aristotle proposed that all matter was composed of a small number of fundamental substances. However, the modern concept of a chemical element was not developed until the 17th century, when Robert Boyle defined an element as a substance that cannot be broken down into simpler substances by chemical means. In 1869, Dmitri Mendeleev created the periodic table, which organized the known elements according to their atomic properties.
The elements are the building blocks of all matter, and they are essential for life. The human body is composed of about 25 different elements, and the vast majority of these are essential for health. The elements are also used in a wide variety of industrial and technological applications. For example, silicon is used to make computer chips, and lithium is used in batteries.