Sodium was an element.
Sodium chloride was the chemical name for salt. (TV: The Sensorites, Image of the Fendahl, Four to Doomsday et al.) Rex Matheson once had low sodium levels in his blood and needed some salt. (TV: Rendition)
Captain Maitland's spectrograph of minerals in the vicinity of the Sense Sphere showed emission wavelengths of "ordinary" oxygen, hydrogen, and sodium, as well as the rare molybdenum. (TV: The Sensorites)