What are some common mistakes students make with molecular geometry?
I'll share some common ones I've observed in my teaching experience. Hopefully others will add...
Trying to make all atoms of the molecule meet the octet rule. Some elements can be exceptions, for example - aluminum will have only six valence electrons in a Lewis structure of something like aluminum triiodide.
Using more or fewer valence electrons than what the formula allows for. In carbon dioxide (
#CO_2#) you can only use 16 valence electrons (4 from the carbon, and 6 from each oxygen). Adding or removing electrons will produce a charged structure (ion).
Failure to put the most electronegative atom in the center of the molecule. Water is an exception to this...