How do you find the "largest dipole moment"?

[Vivian Tan 3F]

This is question 3B on the 2014 Final exam:

Which of the following molecules has the largest dipole moment?
CO
NO
HI
HBr
HF

How do I find the dipole moments of these molecules, and how do I know which one is the "largest"?


Thanks!

[Jamlah Dalie 1K]

HF has the largest dipole moment, you can tell which molecule has the largest by looking on the periodic table, they are usually the pair that are furthest from each other and it is also due to them having the biggest difference in electronegativity, usually the closer two elements are, the weaker the dipole moment.

[Vivian Tan 3F]

How about HBr? And HI?

[Richard_4E]

HBr would have a larger dipole moment than HI since as Jamlah said, there's a greater electronegativity difference between H and Br than between H and I. In other words HBr is more polar and Bromine will attract electrons to itself more.

[Zoe Robertson 2H]

HBr would have a larger dipole moment than HI since as Jamlah said, there's a greater electronegativity difference between H and Br than between H and I. In other words HBr is more polar and Bromine will attract electrons to itself more.

I'm not understanding why HBr has a larger dipole moment than HI. Aren't H and Br closer to each other on the periodic table than H and I? Wouldn't that mean the opposite?

[Chem_Mod]

Dipole moments are indicative of how polar a bond is. So you must find the most polar bond, or bond which has the greatest electronegativity difference.

[Linh Vo 2J]

HBr would have a larger dipole moment than HI since as Jamlah said, there's a greater electronegativity difference between H and Br than between H and I. In other words HBr is more polar and Bromine will attract electrons to itself more.

I'm not understanding why HBr has a larger dipole moment than HI. Aren't H and Br closer to each other on the periodic table than H and I? Wouldn't that mean the opposite?

The reason why HBr has a larger dipole moment is because electonegativity increases across and decreases down the periodic table. Since Br is above I, this means that Br is more electronegative, thus making HBr more electronegative than HI.