How is PCl5 a polyatomic compound and where did the ionic charge of 5 come from?

Question

On the periodic table phosphorus charge is 3- and chloride charge is -1. I'm confused where the ionic charge of 5 came from.

 

I'm told that PCl5 is Polyatomic compound HOWEVER neither element is listed in my list of polyatomic ions (ex: CO3, OH-, NO3 etc), so how is it polyatomic compound when it looks like an ionic compound?

Another example is AlN, that's apparently a polyatomic compound too but neither is a polyatomic ion?

 

Thank you so much in advance

Answer 1

Ions have a charge. Compounds are neutral (no charge).

Polyatomic ions are ions, charged particles, that contain more than one element.

Na⁺ is the sodium ion. it is not polyatomic.

NO₃^- , SO₄^-2 , HCO₃^- are polyatomic ions and contain 2 or more elements.

 

All compounds are polyatomic. If there is only one atom, it would be an element.

 

PCl₅ contains 2 different elements, therefore it is polyatomic, but it is not an ion because it is neutral.

 

The most common valence number for P is 3- but it can also be 5+.

 

When P combines with 5 chloride ions, the P has a 5+ charge.

 

Having said all that, I personally have never heard of calling a compound polyatomic.

 

Elements are made of atoms and compounds are made of molecules. Compounds have more than one element. Molecules also have more than one element with very few exceptions such as the gases H₂ O₂ N₂

 

These are molecules made up of 2 atoms of the same element.