The identity of lithium is determined by its atomic number, which is 3. Lithium is a chemical element that is defined by the number of protons in its nucleus, which is 3. This number distinguishes lithium from other elements on the periodic table, which have different numbers of protons. The number of protons also determines the number of electrons in a neutral atom of lithium. Because the number of electrons determines the chemical properties of an element, the identity of lithium is determined by its atomic number and the unique arrangement of its electrons. In addition to its atomic number, other properties that define lithium include its atomic mass, which is 6.94, and its position in the periodic table, where it is located in the alkali metal group.