The number of valence electrons in phosphorus is +5. Phosphorus, a non-metallic element discovered in 1669 by Hennig Brand, has the atomic symbol of P and an atomic number of 15.
One determines the number of valence electrons in phosphorus by learning the atomic number and knowing the number of electrons in each shell of an atom. A maximum of two electrons exists in the first outer shell, a maximum of eight in the second, a maximum of 18 in the third and a maximum of 32 in the fourth. Since the atomic number for phosphorus is 15, phosphorus has 15 electrons. It has two in the first shell and eight in the second, leaving five electrons in the outermost shell.