1.

Radiowaves can provide information about the molecules found in some regions of space. (i) One molecule found in the coldest regions of outer space has the formula H2CO. This molecule can be represented as: H C H O

Draw the dot-and-cross diagram for this molecule.[3]

(ii)

Use your diagram from (i) to help you describe and explain the shape of H2CO, giving the bond angle. ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... .........................................................................................................................[5] [Total 8 marks]

2.

(a) The strength of metals and metal alloys is due to their strong metallic bonding. Draw a labelled diagram to show a simple model of metallic bonding.

[3]

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(b)

Many beryllium compounds are covalent in character. An example is beryllium chloride. The left-hand box below shows the bonding in a beryllium chloride molecule in the vapour state. Complete the dot-and-cross diagram for this molecule in the right-hand box.

Cl

B

e

Cl C

l B

e

C[2]

l

(c)

The chlorides of the other Group 2 metals are all ionic. Name two physical properties of ionic chlorides which you would expect to be different from those of simple covalent chlorides. State how the properties would differ. ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... .........................................................................................................................[3] [Total 8 marks]

3.

Low sulphur fuel is now a familiar label on the pumps at petrol stations. The removal of sulphur from diesel and petrol significantly reduces the emission of toxic oxides of sulphur from vehicle exhausts. (i) One oxide of sulphur is the gas sulphur dioxide, SO2. One way to represent the bonding in sulphur dioxide is given below.

O = S OUse the structure above to draw a dot-cross diagram in the box below. Show all outer electrons.

O

S

O[3]

(ii)

The actual shape of the sulphur dioxide molecule is V-shaped. Explain why you would predict this shape for the SO2 molecule. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[3] [Total 6 marks]

4.

Atoms react together to form molecules in the dense gas clouds in interstellar space. Molecules of H2S, NH3 and OCS (similar in structure to CO2) have been detected. (i) Complete the dot-and-cross diagram for each molecule in the boxes below.

H

S

H H

H

OH C S N

[3]

(ii)

Use the theory of electron pair repulsion to decide which of the possible shapes below represents the shape of each molecule. Write the formula of each of the molecules H2S, NH3 and OCS underneath its shape.

[3]

(iii)

What is the significance of the wedge ( shape on the left?

) and the dotted line (-------) in the

..................................................................................................................................... .....................................................................................................................................[2] [Total 8 marks]

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5.

A rocket is powered by the reaction between methylhydrazine and dinitrogen tetroxide. 4CH3NHNH2(l) + 5N2O4(l) 4CO2(g) + 12H2O(l) + 9N2(g) A partially completed dot-cross diagram and a full structural formula for methylhydrazine are shown below. (i) Complete the dot-cross diagram for methylhydrazine, showing all the outer shell electrons.H H C H H H H N HA

C H

NN H

HN H

H

B[2]

(ii)

Give approximate values for the bond angles A and B in the methylhydrazine molecule. A ............................................................ B ............................................................[2] [Total 4 marks]

6.

In colder parts of the universe, between stars, molecules have been identified. One such molecule is carbon monoxide, CO. (i) The structure of carbon monoxide is represented as C What type of covalent bond is represented by the arrow? .....................................................................................................................................[1]

O

(ii)

Draw a dot-cross diagram for a molecule of carbon monoxide.

C

O[3]

(iii)

Another molecule found in space is OCS, which has the same shape as CO2. OCS is not stable under the conditions on Earth. We can, however, predict the shape of the molecule using electron pair repulsion theory. Explain this theory and use it to predict the shape of the OCS molecule. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[5] [Total 9 marks]

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