Shapes of Molecules

Question 1

What can be used to predict the shapes of molecules and polyatomic ions?

Answer 1

VSPER ( valence shell electron pair repulsion )

Question 2

Why is the shape of a molecule important?

Answer 2

It will determine its properties and uses.

Question 3

How do you work out the shape of a molecule?

Answer 3

1. the number of electron pairs ( outer electrons, same as group number )
2. How many of the electron pairs are bonded to other atoms and non-bonded.
3. the number of atoms attached to the central atom.

Question 4

How do you work out the number of electron pairs in a molecule or polyatomic ion?

Answer 4

(number of valence e ( group number ) of the central atom (usually first atom)
+ number of atoms attached to central atom ) / 2

** if it is an ion, you subtract the charge if its a positive charge from the top row and you add thew charge if its a negative charge.

Question 5

What are the shapes of molecules where al e- are bonding pairs?

Answer 5

Linear - 2 bonding pairs
Trigonal planer - 3 bonding pairs
Tetrahedral - 4 bonding pairs
Trigonal bipyramidal - 5 bonding pairs
Octahedral - 6 bonding pairs

Question 6

How are shapes of molecules determined?

Answer 6

The shapes adopted by the atoms present based on the arrangement of electron pairs

Question 7

Describe how electron pair repulsions decrease in strength in the order.

Answer 7

Greatest Atrraction/ smallest angle - (non-bonding pair/ non-bonding pair) > (non-bonding pair/ bonding pair) > (bonding pair/bonding pair) Weakest attraction / greatest angle

Question 8

How are bond angles kept as far apart as possible?

Answer 8

Electron pairs are negatively charged and repel each other. They are arranged to minimise repulsion and maximise separation.

Question 9

How many electron pairs gives you an angle of 90 degrees?

Answer 9

6