Phosphorus (P). Diagram of the nuclear composition,electron configuration,chemical data,and valence orbitals of an atom of phosphorus-31 (atomic number: 15),the most common isotope of this element. The nucleus consists of 15 protons (red) and 16 neutrons (orange). 15 electrons (white) occupy available electron shells (rings). The stability of an element's outer (valence) electrons determines its chemical and physical properties. Phosphorus,a solid non-metal,is in group 15,period 3,and the p-block of the periodic table. Its compounds are essential for life. In elemental form it has two main allotropes,white and red phosphorus |