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Posted: Thu Dec 06, 2018 4:25 pm
How do we determine a molecule's polarity by looking at it's VSEPR formula? I know we can draw it out but is there an easier way?
Posted: Thu Dec 06, 2018 5:54 pm
Lone pairs can cause asymmetric shapes in a molecule because they will repel bonds away from them. Depending on the number of lone pairs as seen in the 'E' subscript in the AXE method, a molecule can be identified as polar if they have polar bonds and their shape is asymmetrical in a way that doesn't allow the polar bonds to cancel themselves out. For example H20 is AX2E2. Because Oxygen (the central atom) has two lone pairs, its molecular geometry is bent which causes it to be polar. This can be distinguished from CO2 (AX2) because Carbon (the central atom), doesn't have lone pairs, and the molecular geometry is linear, allowing the polar bonds between carbon and oxygen on either side of carbon to cancel each other out.
Posted: Fri Dec 07, 2018 2:30 pm
The VSEPR format allows you to be able to tell what the molecular geometry is. If the geometry is asymmetrical or the atoms have a large difference in electronegativity, the molecule is polar. Generally, any lone pairs will cause areas of asymmetry.