Phosphorus
Atomic number 15 means that every Phosphorus nucleus contains 15 protons. That proton count is the element's identity: change it and you no longer have Phosphorus.
Start with the nucleus
Atomic number 15 means that every Phosphorus nucleus contains 15 protons. That proton count is the element's identity: change it and you no longer have Phosphorus.
Phosphorus (P) is chemical element 15. It belongs to the nonmetals, and its reference state at room temperature is a solid. Those basic facts are a useful starting point for its chemistry and applications.
In practice, it turns up most often in fertiliser production, biology and matches.
See the atom
Conceptual visual: electron shells are a learning aid, not a literal picture of quantum orbitals.
What this number means
Atomic number 15 means that every Phosphorus nucleus contains 15 protons. That proton count is the element's identity: change it and you no longer have Phosphorus.