Choose from: Br2, H2, BeCl2, CCl4, CH4, H2O, CO2, PH3

Question

a) which have AT LEAST one polar covalent bond

b) that have only nonpolar bonds

 

Answers i have that might not be right:

 

a) H2O, CO2, BeCl2, CCl4

-i dont understand why should it be CO2, BeCl2, CCl4 when they are nonpolar

-isnt there supposed to be also PH3?

b)Br2, H2 , PH3, CH4

- shouldnt there be BeCl2, Br2, H2 , CH4, CCl4, CO2?

Answer 1

The question asks for polar and non polar BONDS, not polar and non polar molecules. So, in (a) all have polar covalent BONDS except for Br2, H2 (which are non polar covalent) and BeCl2 which is ionic. Actually, in checking further, there is not difference in EN values between P and H, so it is a NON polar bond. In (b), Br2 and H2 are non polar covalent. I dont think Lewis dot and VSEPR need to be considered when determining if a BOND is polar, only if the molecule is polsr. 

Answer 2

To answer the first part of the question we must consider the structures of the molecules, both Lewis dot and VSEPR.

 

CO2, BeCl2, CCl4 are all nonpolar because they exhibition symmetry around the central atom. When there is an even distribution of charge, the molecules does not have a dipole, or separation of charge, and is therefore non-polar. For example, the shape of CO2 is linear. The oxygens on either side of carbon pull the negative charge in both directions. PH3 is polar because the Phosphorus atom has a lone pair of electrons (negative charge).

 

To answer the second part of the question, we must know that a polar bond occurs between atoms with a significant difference in electronegativity. The C-O and C-Cl bonds have a significant difference in electronegativity and are therefore polar bonds (even though the molecules they’re in here are non-polar overall due to symmetry.)