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Do we need to memorize that a tetrahedral bond angle is 109.5 degrees if all the atoms bonded to the central atom are the same. Dr. Lavelle approximated the bond angle for trigonal pyramidal from the bond angle of tetrahedral.
I'm not sure how essential it would be to memorize the angles, but I feel like there could be questions dealing with the bond angles on the final? I think it's still helpful to know the bond angles, maybe not exactly the number but their length relative to the other shapes.
I believe Dr. Lavelle said that we don't need to memorize exact bond angles, but we need to know when bond angles differ and the causes for those differences. An example is like how a molecule with a trigonal pyramidal shape(such as SO32-) has smaller angles than a tetrahedral one(like SO42-) because lone pairs exert more repulsion than bonded pairs. Feel free to correct me if I'm wrong though
Yes, I think Dylan is correct! It's important to know the order of increasing distortion between regions of electron density. Lone pair-lone pair > lone-pair-bonded pair > bonded pair-bonded pair. So at least know that trigonal pyramidal has a slightly smaller bond angle than tetrahedral due to the repulsion exerted by the lone pair.
I don't think remembering the bonding angle (109.5) is important but knowing how the bonding angle changes depending on the number of lone pairs presence is more important. Lone pair(s) strongly repulse, causing a shift in bonding angle.
When dealing with shapes like tetrahedral(109.5 degrees) and trigonal planar(120 degrees), those shapes have consistent bond angles, so I feel that it's best to memorize those. However, for shapes like trigonal pyramidal, seesaw, bent, etc., knowing if they're above/below 109.5 or above/below 120 is usually what you need to know.
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