Determining Molecular Shape and Polarity

Question 1

What is the VSEPR theory?

Answer 1

the Valence Shell Electron Pair Repulsion explains that each pair of electrons repel each other so they are as far apart as possible
-based on 5 basic shapes (geometric arrangement)

Question 2

What is the method to determine the molecular shape of a molecule?

Answer 2

1. draw the lewis structure of the compound
2. determine total # of electron groups (EG) around the CENTRAL atom (each bond and lone pair counts as 1)
3. determine the EA (electron arrangement) based on # of EG
4. determine molecular shape (MS) by erasing lines of the EA if there is a lone pair in the arrangement and explaining the structure now

Question 3

What are the 5 basic molecular shapes?

Answer 3

2 groups: linear - 180 
3 groups: trigonal planar- 120
4 groups: tetrahedral- 109.5
5 groups: trigonal bipyramidal- 90, 120, 180
6 groups: octahedral- 90, 180

Question 4

What are the variations due to lone pairs for the 5 basic molecular shapes?

Answer 4

3 groups: 1 LP=bent 120
4 groups: 
-1 LP=trigonal pyramid
-2 LP= bent 109.5 
5 groups: 
-1 LP= seesaw
-2 LP= T-shape 
-3 LP= linear 
6 groups:
-1 LP= square pyramid 
-2 LP= square planar 
-3 LP= T-shape 
-4 LP= linear

Question 5

Why are there different electron arrangements for different molecules?

Answer 5

each electron arrangement is meant to achieve minimal electron repulsion between atoms in a molecule

Question 6

How do you determine the polarity of a molecule?

Answer 6

• using the symmetry shape test
• compare the arms of the atom ( same=np, different =p)
• To be non-polar, the molecule must have a symmetrical shape AND have same arms*

Question 7

What is H2O’s polarity?

Answer 7

polar compound (any molecule that is polar will form DD with water and dissolve)