Electric dipole moment in gaseous species.

[V0ODO0CH1LD]

Homework Statement

Consider the following species in the gaseous state: $NF_3, \ BeF_2, \ BCl_3, \ KrF_4 \ and \ SeO^{2-}_4$.
Which of them have electric dipole moment?

Homework Equations

The Attempt at a Solution

I tried google, but I can't figure out how to check that..

 

[AGNuke]

Can you draw their representative structures, like you draw tetrahedral structure for methane? That can give you the clue.

 

[V0ODO0CH1LD]

How is drawing the representative structures supposed to give me a clue on which species have electric dipole moment? Is it like, in the case with $BeF_2$, where $Be$ is left with a positive charge of 2+ and each $F$ with a negative charge of 1-. So it will have electric dipole moment?

 

[AGNuke]

Example to what I said:

BeF₂ in gaseous form is a linear molecule, like F---Be---F, so the dipoles are F---Be and Be---F. Now can you determine the net dipole moment?

What I asked you is to draw the structures of molecules using VBT and VSEPR theory. Like in the case of NF₃