What is an element?
An element is a pure substance made of only one type of atom, defined by its number of protons. There are 118 known elements, from hydrogen to oganesson, listed in the periodic table.
Each element has a unique atomic number, which is the number of protons in the nucleus of its atoms. Hydrogen has 1 proton, carbon has 6, oxygen has 8 and gold has 79. Elements cannot be broken down into simpler substances by chemical reactions. They are the basic building blocks of all matter.
About 90 elements occur naturally on Earth. The rest have been created in laboratories, usually by smashing atoms together in particle accelerators. Many of these synthetic elements are highly unstable and exist for only fractions of a second. The most recent were officially named in 2016.
The periodic table
Russian chemist Dmitri Mendeleev created an early periodic table in 1869, arranging elements by their properties and leaving gaps for undiscovered ones. Today, the table is arranged by atomic number in rows called periods and columns called groups, where elements share similar properties.
Did You Know?
Hydrogen is the most abundant element in the universe, making up about three-quarters of all normal matter. Oxygen is the most abundant element in Earth's crust.