Nitrogen (N). Diagram showing the nuclear composition and electron configuration of an atom of nitrogen-14 (atomic number: 7), the most common isotope of the element nitrogen. The nucleus consists of 7 protons (red) and 7 neutrons (yellow). Seven 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. Nitrogen, vital for life on Earth, is a non-metal in group 15, period 2, and the p-block of the periodic table. As a gas (N2) it forms 78 percent of the atmosphere. It liquefies at minus 196 degrees Celsius.