Sodium

Sodium was an element.

Sodium chloride was the chemical name for salt. (TV: The Sensorites, Image of the Fendahl, Four to Doomsday et al.)

Sodium ethoxide (C₂H₅ONa) was the derivative of sodium acting on ethyl alcohol. (TV: The Power of the Daleks)

Rex Matheson had low sodium levels in his blood and needed some salt. (TV: Rendition)