Phosphorus

Phosphorus is atom number 15 — every Phosphorus atom has exactly 15 protons in its center, and that number is what makes it Phosphorus and nothing else. Its symbol is P. At room temperature it is a solid.

Phosphorus is a chemical element with symbol P and atomic number 15. As an element, phosphorus exists in two major forms—white phosphorus and red phosphorus—but due to its high reactivity, phosphorus is never found as a free element on Earth. Instead phosphorus-containing minerals are almost always present in their maximally oxidised state, as inorganic phosphate rocks.

Summary from the source dataset, derived from Wikipedia (CC BY-SA 3.0) · original article

Phosphorus sits in period 3, group 15 of the p-block. Its 15 electrons fill shells of 2, 8, 5 — written as [Ne] 3s2 3p3. Its electronegativity is 2.19 on the Pauling scale, and pulling the first electron off takes 1011.8 kJ/mol. The outermost shell holds 5 electrons — the ones that do all the chemistry.

Full configuration: 1s2 2s2 2p6 3s2 3p3
Ionization energies (kJ/mol): 1011.8, 1907, 2914.1, 4963.6, 6273.9, 21267, 25431, 29872 … (15 published)
Electron affinity: 72.037 kJ/mol · Electronegativity (Pauling): 2.19
Density: 1.823 g/cm³ · melts — · boils —

Values exactly as published — see where the data comes from.