Isotopes of phosphorus

Although phosphorus (₁₅P) has 22 known isotopes from P to P, only P is stable; Phosphorus is thus considered a monoisotopic element. P is also the only naturally occurring isotopes of phosphorus, so phosphorus is considered a mononuclidic element as well. The longest-lived radioactive isotopes are P with a half-life of 25.35 days and P with a half-life of 14.269 days. All others have half-lives of under 2.5 minutes, most under a second.