Here's why:
* Valence electrons: Phosphorus has 5 valence electrons, and chlorine has 7.
* Octet rule: Atoms tend to gain, lose, or share electrons to achieve a stable configuration of 8 valence electrons (octet rule).
* Bonding: Phosphorus needs to gain 3 electrons to achieve a full octet. Each chlorine atom needs to gain 1 electron. This means that 3 chlorine atoms will bond with one phosphorus atom, sharing 1 electron each.
Therefore, 3 atoms of chlorine are likely to combine with one atom of phosphorus to form PCl₃.
