Prep work for unit 2.1 of the Edexcel AS Chemistry course

1. AS Chemistry prep - 2.1 ‘Shapes of molecules and ions’
• This sheet of problems is designed to help you learn and understand the material we cover in
class.
• In addition to attempting these problems you should be reading around the topic, which is
covered by pages 144-153 in your textbooks.
• We will be spending one week on this topic before moving on to 2.2, you may attempt these
problems at any point after we have started looking at 2.1 but I would like your completed
answers handed in at our first lesson on topic 2.2.
Exercise 1 - Dot- cross diagrams
Draw dot-cross diagrams for the following covalent molecules:
1. CH4
2. CCl4
3. BBr3
4. NH3
5. PF5
Exercise 2 - VSEPR theory basics
1. Explain how VSEPR theory is used to predict the shapes of covalent molecules.
2. Use VSEPR to predict the shapes of the following molecules:
a. BeCl2
b. BCl3
c. CCl4
d. PCl5
e. SF6 Be sure to include names for the shapes and bond
angles
Exercise 3 - The effect of lone- pairs
1. Explain what is meant by the term ‘lone-pair’ and why they are important in VSEPR theory.
2. Use VSEPR to predict the shapes of the following molecules:
a. NH3
b. H2O
c. H2S
d. XeF4 Be sure to include names for the shapes and bond
angles
Exercise 4 - The shapes of ions
Use VSEPR to predict the shapes of the following ions:
1. NH4+
2. MnO4-
3. I3- Be sure to include names for the shapes and bond
angles
Exercise 5 - Summary of VSEPR theory
1. Write a ‘recipe’ or list of instructions for predicting the shapes of molecules using VSEPR
theory that another student could easily follow.
2. Use the net on the attached sheet to build your own octahedron shape.
Extension
Impressive amounts of extra brownie points are available for anyone who is bold enough to build me
a 3D model of a trigonal bipyramid .