Exercise 3 solution

Guide (Chemical polarity article): difference below 0.5 nonpolar; roughly 0.5 to 2.0
polar; above 2.0 ionic. The Electronegativity article itself gives no cut-offs, so
this is a rough guide.

Differences (run in Python, larger value minus smaller):
N-H: 3.04 - 2.20 = 0.84  -> between 0.5 and 2.0: polar
H-F: 3.98 - 2.20 = 1.78  -> between 0.5 and 2.0: polar (the largest of the three)
C-O: 3.44 - 2.55 = 0.89  -> between 0.5 and 2.0: polar
None of the three is below 0.5 or above 2.0.

In each polar bond the more electronegative atom (N, F, O) is at the negative end of
the dipole, as the Electronegativity article says.

Why a molecule with polar bonds can be nonpolar: the Chemical polarity article says the
C=O bonds in carbon dioxide are polar, but "the geometry of CO2 is linear so that the
two bond dipole moments cancel". The two bonds pull in opposite directions by equal
amounts, so there is no net dipole. Methane works the same way through its symmetric
tetrahedral arrangement. Water is the contrast: its bent shape means the two O-H dipoles
do not cancel, so water is polar.

Not covered by the pages: why the numbers behave this way (check, a deeper topic).