Shapes of molecules

Question 1

What does molecular shape depend on?

Answer 1

Molecules and molecular ions come in loads of different shapes.

The molecular shape depends on the number of electron pairs around the central atom.

Question 2

Whatbi the difference between lone pairs and bonding pairs of electrons?

Answer 2

Question 3

Why do electron pairs repel each other?

Answer 3

Electronare all negatively charged so electrons will repel each other as much as they can.

Question 4

What factor influences electron repulsion?

Answer 4

The type of electron pair affects how much it repels other electron pairs - lone pairs repel more than bonding pairs.

Question 5

Describe electron pair repulsion theory. How does this affect angles between electron pairs?

Answer 5

Lone pairs repel more than bonding pairs. This means the greatest angles are between lone pairs of electrons, and bond angles between bonding pairs are ofetn reduced because they are pushed together by lone pair repulsion.

• lone pair/lone pair angles are the biggest
• lone pair/ bonding par angles are the second biggest
• bonding pair/bonding pair angles are the smallest

Question 6

Methane, Ammonia and water all have 4 pairs of electrons in the the outer shells of their central atom. Draw them and explain their shapes.

Answer 6

For ammonia, think of it as a pyramid shape with three 107° bond angle as the base.

Question 7

What is the method for predicting the shape of molecules?

Answer 7

Question 8

==What are the common shapes of molecules you need to be able to draw?

Answer 8