What are elements?
What are elements? Elements are pure substances made of atoms that all have the same number of protons, called the atomic number, so an element cannot be broken into simpler substances by ordinary chemical reactions.
Hydrogen (1 proton), carbon (6) and gold (79) are examples. There are 118 known chemical elements, about 94 of them occurring naturally, and each has its own symbol, name, atomic mass and place on the periodic table. To see how atomic number, groups and periods organise every known substance, explore the periodic table of chemical elements at your own pace.
Atoms of the same element can differ in neutron count, which makes them isotopes, but they still behave as the same element chemically. Elements combine in fixed ratios to form compounds, such as water (hydrogen and oxygen) or table salt (sodium and chlorine), and they mix without bonding to form mixtures like air. The same series of answers also covers “how many elements are in the periodic table”.
Everything you can touch, from metals and gases to the matter in living cells, is built from these basic substances, which is why elements are often called the building blocks of matter. Elements differ from compounds and mixtures. Another common question on this site is “where are metals located on the periodic table of elements”.
A compound such as carbon dioxide has a fixed formula and properties unlike those of its elements, while a mixture such as air or seawater can be separated by physical means. Most elements are metals, a smaller group are nonmetals, and a handful are metalloids. Readers also ask “what are the 5 elements”, which has its own short answer.
About 94 elements occur naturally, from hydrogen and helium made in the Big Bang to heavier elements forged in stars and supernovae, and the rest, from americium (95) to oganesson (118), are synthetic elements made in laboratories. Each element is given a one- or two-letter symbol such as H, O, Fe or Au and is listed by atomic number.
Some, including gold, copper, iron, silver, lead, tin and mercury, have been known since ancient times, while others were found in the last century using particle accelerators. Isotopes of an element share chemical behavior but differ in mass, and some isotopes are radioactive. In science, each element is identified by its atomic number, and properties such as density and melting point help scientists tell it apart from every other element.