Shapes of Covalent Molecules

Question 1

What is the shape of a covalent molecule determined by?

Answer 1

The angles between bonds that join atoms together

Question 2

What does Sidgewick and Powell’s theory - VSEPR (Valence Shell Electron Pair Repulsion) - conclude?

Answer 2

Electron pairs in the outer shell of atoms try to stay as far apart as possible to reduce electrostatic repulsion.

Molecules take up the shape that minimises the repulsion between electron pairs within the molecule.

Question 3

What is the bond angle in a ‘linear’ molecule?

Answer 3

180 degrees

Question 4

What is the bond angle in a ‘bent’ molecules?

Answer 4

109.5 degrees

Question 5

What ‘bent’ molecule has a different bond angle?

Answer 5

Water, 104.5 degrees

Question 6

What is the only possible bond angle in a ‘linear’ molecule?

Answer 6

180 degrees

Question 7

What is the bond angle in a ‘tetrahedral’ molecule?

Answer 7

109.5 degrees

Question 8

What is the bond angle in a ‘trigonal planar’ molecule?

Answer 8

120 degrees

Question 9

What is the bond angle in a ‘trigonal pyramidal’ molecule?

Answer 9

107 degrees

Question 10

What is the bond angle in an ‘octahedral’ molecule?

Answer 10

90 degrees

Question 11

How many atoms can there be in a ‘linear’ molecule?

Answer 11

2 or 3

Question 12

How many atoms are there in a ‘bent’ molecule?

Answer 12

3

Question 13

How many atoms are there in a ‘tetrahedral’ molecule?

Answer 13

5

Question 14

How many atoms are there in a ‘trigonal planar’ molecule?

Answer 14

4

Question 15

How many atoms are there in a ‘trigonal pyramidal’ molecule?

Answer 15

4

Question 16

Are there any unshared pair of electrons in ‘linear’ molecules?

Answer 16

In a ‘linear’ molecule with 3 atoms, there will be no unshared pairs of electrons; if there were, the molecule would be non linear or ‘bent.’

In a ‘linear’ molecule with 2 atoms, any unshared pairs of electrons will not affect the bond angle.

Question 17

What group typically form ‘bent’ molecules and why?

Answer 17

Group 6 as there are 2 pairs of unshared electrons in elements such as oxygen and silicon (both group 6) which will repel any other atoms downwards.

Question 18

What group typically form ‘tetrahedral’ molecules and are there any unshared pairs of electrons?

Answer 18

Group 4 elements, no unshared pairs of electrons

Question 19

What group typically form ‘trigonal planar’ molecules and are there any unshared pairs of electrons?

Answer 19

Group 3 elements, no unshared electrons

Question 20

What group typically form ‘trigonal pyramidal’ molecules and are there any unshared pairs of electrons?

Answer 20

Group 5 elements, 1 pair of unshared electrons will repel the bonded pairs down.

Question 21

Give an example of 2 ‘linear’ molecules.

Answer 21

CO2, O2

Question 22

Give an example of 2 ‘bent’ molecules.

Answer 22

H2O, SH2

Question 23

Give an example of a ‘tetrahedral’ molecule.

Answer 23

CH4

Question 24

Give an example of a ‘trigonal planar’ molecule.

Answer 24

BF3

Question 25

Give an example of a ‘trigonal pyramidal’ molecule.

Answer 25

NF3

Question 26

Give an example of an ‘octahedral’ molecule.

Answer 26

SF6