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Predicting Molecular Shapes with More than One Central Atom
Problem: Determine the shape around each of the central atoms in acetone, (CH3)2C=O.
Solution: 1. Lewis structure:
2. Each CH 3 group is AX4; its electron-group arrangement is tetrahedral. The third C is AX3, a trigonal planar arrangement.
3. The CH3 groups should have about 109.5° bond angles. The C=O double bond will compress C-C-C angle to less than the ideal 120°.
4. Shapes: CH3 groups are tetrahedral, the other C atom is trigonal planar.
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