How to determine the bond angle based on the formula of molecules?
Just with the number of atoms, you can't do that. The angle will minimize the energy of the molecule. It is possible to simulate those molecules in a computer to find the angles, and there are approximate rules how to estimate the angles for various combinations of atoms.
Well many complex questions may be placed over this
the question becomes very diverse AND DIVERSE
firstly you must refer to vsepr theory
then facts like "lone pair lone pair" repulsion are more etc
adding to it someone mAY put forward the favorite exceptions like "drago's rule"
You need to know more than just an overall formula. Think structural isomers. For example C3H6 can be either propene or cyclopropane, and the bond angles between carbon atoms will be substantially different in each case.
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