Soddy, Frederick (1877-1956), an English chemist and physicist. A pioneer of research into radioactivity, Soddy, with Ernest Rutherford, discovered (1900-02) that elements are changed through radioactivity. He also discovered that an element can be made up of atoms that are chemically identical, but have different weights. In 1913 Soddy introduced the term isotope for such atoms. He was awarded the Nobel Prize for chemistry in 1921.

Soddy was born in Sussex and graduated from Oxford University in 1898. He taught chemistry at Canadian and British universities until his retirement in 1936.