im not to sure if thats so... The periodic table does not disclose the identity of the di-atomic elements you just gotta remember them. Most elements are represented as monoatomic substances those exclusions i belive are only the diatomic elements, carbon, silicon, and phosphorus.... i might be wrong but thats my two cents... this is wikipedias explanation about the structure of white phosphorus.
"White phosphorus, or yellow phosphorus, or simply tetraphosphorus (P4) exists as individual molecules made up of four atoms in a tetrahedral arrangement, resulting in very high ring strain and instability. It contains 6 single bonds."