Phosphorus and fluorine can combine to form two different compounds. One is phosphorus trifluoride (PF3) and the other is phosphorus pentafluoride (PF5). Naturally occurring phosphorus can occur in different forms but the most common form of elemental phosphorus is P4 (white or red phosphorus). Fluorine is a gas consisting of two fluorine atoms bonded together (F2). The balanced chemical equations are shown below:
P4 + 6 F2 ---> 4 PF3
P4 + 10 F2 ---> 4 PF5
As you can see, both chemical reactions require an excess of fluorine as compared to phosphorus (6 molecules of F2 to every 1 molecule of P4 in the first reaction and 10 molecules of F2 to every 1 molecule of P4 in the second reaction).