choose the molecule or compound that exhibits dispersion forces as its strongest intermolecular force.
a) HF
b) Cl2
c) NaCl
d) CO
e) all of these have intermolecular forces stronger than dispersion.

I know the answer is B but how would you solve this question on an exam. Im trying to go over this study guide before my exam

Question

choose the molecule or compound that exhibits dispersion forces as its strongest intermolecular force.
a) HF
b) Cl2
c) NaCl
d) CO
e) all of these have intermolecular forces stronger than dispersion.

I know the answer is B but how would you solve this question on an exam. Im trying to go over this study guide before my exam

sweetburger · Answer

Well there is no electronegativity difference in Cl2. This is because both atoms composing the molecule have identical EN's because they are the same element. Because there is no polarity in Cl2 the only intermolecular interaction that can occur is London Dispersion Forces.

alinaalba · Answer

how would you find the electronegativity between all the other answer choices in case an element like cl2 doesn't appear on the exam.

sweetburger · Answer

Well you wouldn't be able to find the EN's of each element. But say you run into something like I2. I2, has no en difference. I determined that without knowing what the EN of I is. 
So basically if you have a compound/molecule made up of different elements you will have some degree of polarity.