How can I identify dipoles in molecules?

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Answer 1 · 2015-06-04T21:52:55

You look for electronegativity differences between the atoms that are bonded to each other.

A bond dipole depends on electronegativity differences (#Δ"EN"#) between the atoms in the bond.

This causes the electrons in the bond to spend more time around one atom than the other.

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For example, in #"HCl"#, the #"Cl"# is more electronegative than #"H"#, so the electrons spend more time around #"Cl"# than #"H"#.

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We indicate a bond dipole by an arrow with a "+" at one end and pointing towards the negative end of the bond.

If #Δ"EN" < 0.5#, we usually say that the bond is ionic.

EXAMPLE

Identify the bond dipoles on chloromethane, #"CH"_3"C"l#.

Solution

The structure of chloromethane is

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#Δ"EN"# for the #"C-H"# bond is 0.4. The #"C-H"# bond is nonpolar.

#Δ"EN"# for the #"C-Cl"# bond is 0.6. The #"C-Cl"# bond is polar.

The #"Cl"# atom is the negative end of the bond, so there is a #"C-Cl"# bond dipole.

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