The electronegativity difference #(Delta"EN")# between two bonded atoms determines the bond character. A #Delta"EN"##<=0.4# is a nonpolar covalent bond. A #Delta"EN"##>0.4<1.7# is considered a polar covalent bond. A #Delta"EN"##>=2.0# is ionic. #Delta"EN"##>1.6<2.0# is polar covalent if a nonmetal is bonded to another nonmetal, and ionic if a metal is bonded to a nonmetal.
The #"EN"# of carbon is 2.55. The #"EN"# of oxygen is 3.04. The #Delta"EN"## = 3.04-2.55=0.49#, which means the C=O bond is mostly nonpolar with a slight polar character.
The #"EN"# of fluorine is 3.98. The #Delta"EN"# of the F-F bond is #3.98-3.98=0#. The F-F bond is completely nonpolar covalent.
Refer to the following website for an electronegativity chart.
https://en.wikipedia.org/wiki/Electronegativity
