any given atom has a propensity to attract electrons which is known as their electronegativity, the greater their electronegativity the more electrons they want to pull
that being said when these atoms form bonds, depending on their electronegativities the way they might share these electrons is going to be different.
take oxygen and hydrogen for example, hydrogen has a much lower electronegativity (2.2) value than oxygen (3.5) so the electrons, will be pulled by the greedy oxygen more than the hydrogen resulting in the bond becoming polar.
however it is important to draw and understand bond dipoles (the arrows showing where the e- are being pulled) because although a single bond may be polar the entire molecule might not be because the polar bonds are canceling eachother out by pulling in equal and opposite directions.
ie ch4, in each individual bond between carbon and hydrogen there is polarity but because of the way the molecule is arranged, bond dipoles highlighting the individual bond polarities cancel out
i hope this is somewhat okay, it's been a while since I've done Chem, so this might be a little confusing, but this person kinda sums up IM forces and polarity and it's a lot more detailed than what I said and possibly more accurate lol
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