Shapes of Molecules and Ions

Question 1

What is the Electron Pair Repulsion theory?

Answer 1

• The groups of electrons surrounding the centre atom of a molecule determines it’s shape
• Electrons will repel each other so that they are as far apart as possible
• Different numbers of electron groups result in different 3D shapes

Question 2

Linear

Answer 2

No. of Bonded groups = 2
Bond Angle = 180
No. of Lone pairs = 0

Question 3

Trigonal Planar

Answer 3

No. of Bonded groups = 3
Bond Angle = 120
No. of Lone pairs = 0

Question 4

Tetrahedral

Answer 4

No. of Bonded groups = 4
Bond Angle = 109.5
No. of Lone pairs = 0
Eg. CH4

Question 5

Trigonal Pyramidal

Answer 5

No. of Bonded groups = 3
Bond Angle = 107
No. of Lone pairs = 1
Eg. NH3

Question 6

Octahedral

Answer 6

No. of Bonded groups = 6
Bond Angle = 90
No. of Lone pairs = 0

Question 7

Non-linear

Answer 7

No. of Bonded groups = 2
Bond Angle = 104.5
No. of Lone pairs = 2
Eg. H2O

Question 8

Trigonal Bipyramidal

Answer 8

No. of Bonded groups = 5

No. of Lone pairs = 2

Question 9

Bonded-pair and lone-pair repulsions

Answer 9

• Lone pairs repel more strongly as they are closer to the central atom and they occupy more space.
• Bond angle is reduced by about 2.5 degrees for each lone pair