Who suggested the word isotope to Frederick Soddy?

Margaret Todd suggested the word “isotope” to Frederick Soddy.

Todd was a Scottish physician, writer, and family friend of Soddy. In 1913, while Soddy was explaining his research on radioactive elements, she proposed “isotope,” built from Greek words meaning “same place.” The name captured the puzzle Soddy was trying to describe: atoms with different masses could occupy the same position in the periodic table because they belonged to the same element.

The concept emerged from radioactive decay chains. Chemists found that some supposedly different radioelements could not be separated chemically, even though they had different radioactive behavior. The later discovery of the neutron explained why: isotopes have the same number of protons but different numbers of neutrons.

Soddy popularized the term and received the 1921 Nobel Prize in Chemistry partly for his work on isotopes. Todd’s contribution is often overlooked because she was not the principal laboratory researcher, but her suggested name became standard scientific vocabulary.