Sodium is a metallic element on the periodic table with an atomic number of 11 and an atomic mass of 22.98 amu. This atomic mass is calculated by adding together the number of protons and neutrons present in the atom's nucleus. Sodium was discovered by Sir Humphrey Davy in 1807.
In addition to protons and neutrons, an atom consists of additional subatomic particles called electrons. Electrons orbit the nucleus in a cloud, but are so small when compared to protons and neutrons that their mass is not included in the calculation for atomic mass. Sodium's atomic nucleus contains 11 electrons.