Sodium

Sodium is a chemical element, symbol Na and atomic number 11.

It is a soft silvery metal which is one of the alkali metals. It is not found in the pure state in nature but is very abundant in the form of compounds, for example in common salt. It burns with a yellow flame.

Na⁺: metal ion, main cation in the extracellular environment, important for maintaining osmotic pressure and water balance. It is transported through the plasma membrane by the sodium pump.