Here's why:
* Electronegativity: Phosphorus and iodine have relatively similar electronegativities. Electronegativity is the ability of an atom to attract electrons towards itself in a chemical bond. The difference in electronegativity between phosphorus and iodine is not large enough to create an ionic bond.
* Sharing of electrons: Since they have similar electronegativity, phosphorus and iodine share electrons to achieve a stable electron configuration. This electron sharing is the defining characteristic of a covalent bond.
Therefore, the bond in phosphorus iodide (PI3) is covalent.
