Gallium (Ga). Diagram of the nuclear composition and electron configuration of an atom of gallium-69 (atomic number: 31), the most common isotope of this element. The nucleus consists of 31 protons (red) and 38 neutrons (yellow). 31 electrons (white) bind to the nucleus, successively occupying available electron shells (rings). The stability of an element's outer electrons determines its chemical and physical properties. Gallium is a post-transition metal in group 13, period 4, and the p-block of the periodic table. It is one of the elements used in semiconductors, forming the basis of computer technology. It has a melting point of 30 degrees Celsius.