Elemental phosphorus (P) is composed of 4 atoms. How can the periodic table show this? ?

This is for personal knowledge. I've been reading a chemistry book but can't recall how to discover the number of atoms in an element. The periodic table should disclose this information, correct?
Update: Well suppose the textbook read, elemental phosphorus (P) is composed of how many atoms? I looked in the back of the book and found the answer to be (4). How could I have found this information on my own though, without scientific means?
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