5 VSEPR VSEPR: Valence Shell Electron Pair Repulsion The pairs of valence electrons in a molecule want to be as far apart from each other as possible.VSEPR allows us to predict the geometry or shape of the molecule.
6 VSEPRTo determine the shape of the molecule you need to count the number of bonded atoms and the number of lone pairs on the center atom of the Lewis structure.A double or triple bond only counts as 1 bonded atom.
7 2 Bonded Atoms 0 Lone Pairs Ex: CO2This is a linear shapeLinear molecules have a bond angle of 180°180°O C O●●
8 3 Bonded Atoms 0 Lone Pairs Ex: CH2OThis is a trigonal planar shapeTrigonal planar has a bond angle of 120°HC O●●120°
9 N H O 2 Bonded Atoms 1 Lone Pair Ex: HNO This is a bent shape This bent has a bond angle of 120°NH O●●120°
10 4 Bonded Atoms 0 Lone Pairs Ex: CH4 (AKA methane)This is a tetrahedral shapeTetrahedral has a bond angle of 109.5°HH C H109.5°
11 H N H H 3 Bonded Atoms 1 Lone Pair Ex: NH3 (AKA ammonia) This shape is trigonal pyramidalTrigonal pyramidal has a bond angle of 109.5°H N HH●●109.5°
12 2 Bonded Atoms 2 Lone Pairs Ex: H2O (AKA water)This shape is bentThis bent has a bond angle of 109.5°O HH●●109.5°
13 PracticeDraw the Lewis structure and predict the shape and bond angle for the following molecules:SiCl4SI2HCNBrPS