* Definition of Heavy Metals: Heavy metals are generally defined as elements with high atomic weights and densities. They often have atomic numbers greater than 20.

* Sodium's Atomic Weight: Sodium has an atomic number of 11 and an atomic weight of 22.99. It is a relatively light element.

* Toxicological Properties: Heavy metals are often associated with toxicity due to their ability to disrupt biological processes. While sodium is essential for human life, it can become toxic in high concentrations. However, its toxicity is not due to its heavy metal properties.

In summary: Sodium is not considered a heavy metal because it has a low atomic weight and is not typically associated with the toxicological properties often seen in heavy metals.