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How exactly do you determine if a molecule is polar or nonpolar? I understand it mainly regards to dipoles canceling out or not, but can anybody elucidate this concept, I'm not quite fully understanding. Thanks!
If the molecule has mirror symmetry, the dipoles will cancel and the net dipole will be zero, therefore it'll be nonpolar. Monatomic compounds will be nonpolar since there's no electronegativity difference. If there's not symmetry and it's polyatomic, often the more electronegative species will pull electrons towards it creating polarity. Just look at the electronegativity difference to determine if this will be the case.
Generally, you can look at the terminal toms to determine whether a structure will be polar or polar. With linear, trigonal planar, and tetrahedral structures, if the terminal atoms are the same the molecules will be nonpolar. But if the terminal atoms are different, the molecules will be polar. Regarding bent and pyramidal structures, the molecule will be polar regardless of whether or not the terminal toms are the same or different
Additionally, there is a table on page 113 in the textbook that helped me a lot with understanding polar and nonpolar. It also helped visualize polar and nonpolar with the shape of the molecule and VSEPR formula, withe examples. The figure is 2E.7 on page 113.
Another thing to remember when determining polarity is that many of these structures are 3 dimensional. For example, with CH2Cl2, placing the Cl atoms opposite each other and placing the H atoms opposite each other may seem like the dipoles would cancel, however due to the 3 dimensional shape the dipoles don't cancel and the molecule is still polar.
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