AS LEVEL CHEMISTRY

ASSESSMENT POINT 2
PAPER 1 - TOPICS 1 AND 3
Answer all questions
Max 80 marks

	
Name		……………………………………………………………..

Mark		……../80	……....%	Grade ………

1.     (a)     Define the term relative atomic mass.
An organic fertiliser was analysed using a mass spectrometer. The spectrum showed that the nitrogen in the fertiliser was made up of 95.12% 14N and 4.88% 15N
Calculate the relative atomic mass of the nitrogen found in this organic fertiliser.
Give your answer to two decimal places.
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(4)
(b)     In a mass spectrometer, under the same conditions, 14N+ and 15N+ ions travel at different speeds. State the property of these ions that causes them to travel at different speeds.
State one change in the operation of the mass spectrometer that will change the speed of an ion.
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(2)
(c)     Organic fertilisers contain a higher proportion of 15N atoms than are found in synthetic fertilisers.
State and explain whether or not you would expect the chemical reactions of the nitrogen compounds in the synthetic fertiliser to be different from those in the organic fertiliser. Assume that the nitrogen compounds in each fertiliser are the same.
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(2)
(Total 8 marks)

2.      (a)     In 1963, krypton was found to react with fluorine. State why this discovery was unexpected.
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(1)

      (b)      Use a suitable model of atomic structure to explain the following experimental observations.
(i)      The first ionisation energy of krypton is greater than that of bromine.
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(ii)     The first ionisation energy of aluminium is less than the first ionisation energy of magnesium.
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(4)
(Total 5 marks)
 
3.	Use the Periodic Table and your knowledge of electron arrangement to write the formula of lithium nitride.
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(1)
(Total 1 mark)

4.	Predict whether an atom of 88Sr will have an atomic radius that is larger than, smaller than or the same as the atomic radius of 87Rb. Explain your answer.
Atomic radius of 88Sr compared to 87Rb .........................................................
Explanation ....................................................................................................
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(3)
(Total 3 marks)
 5.    (a)     Explain why sodium has a lower melting point than magnesium.
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(3)

(b)     Sodium reacts with ammonia to form the compound NaNH2 which contains the NH2– ion. Draw the shape of the NH2– ion, including any lone pairs of electrons.
Name the shape made by the three atoms in the NH2– ion.
Shape of NH2–

Name of shape ............................................................................................
(2)
(c)      In terms of its electronic configuration, give one reason why neon does not form compounds with sodium.
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(1)
(Total 6 marks)
 
6.      There are several types of crystal structure and bonding shown by elements and compounds.
(a)     (i)      Name the type of bonding in the element sodium.
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(1)
(ii)     Use your knowledge of structure and bonding to draw a diagram that shows how the particles are arranged in a crystal of sodium.
You should identify the particles and show a minimum of six particles in a two-dimensional diagram.

(2)
(b)     Sodium reacts with chlorine to form sodium chloride.
(i)      Name the type of bonding in sodium chloride.
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(1)
(ii)     Explain why the melting point of sodium chloride is high.
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 (2)

(c)     The table below shows the melting points of some sodium halides.
 
 	NaCl	NaBr	NaI	
Melting point /K	1074	1020	920	
Suggest why the melting point of sodium iodide is lower than the melting point of sodium bromide.
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(1)
(Total 7 marks)
 
7.      (a)     (i)      Complete the electronic configuration of aluminium.
1s2 .......................................................................................................
(ii)     State the block in the Periodic Table to which aluminium belongs.
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(2)
(b)     Describe the bonding in metals.
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(2)
(c)     Explain why the melting point of magnesium is higher than that of sodium.
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(3)
(d)     Explain how metals conduct electricity.
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(2)
(Total 9 marks)

8.       A molecule of ClF3 reacts with a molecule of AsF5 as shown in the following equation.
ClF3 + AsF5 → ClF2+ + AsF6–
Use your understanding of electron pair repulsion to draw the shape of the AsF5 molecule and the shape of the ClF2+ ion. Include any lone pairs of electrons.
Name the shape made by the atoms in the AsF5 molecule and in the ClF2+ ion.
Predict the bond angle in the ClF2+ ion.
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 (Total 5 marks)
 
9.      (a)     Name the strongest type of intermolecular force between hydrogen fluoride molecules and draw a diagram to illustrate how two molecules of HF are attracted to each other.
In your diagram show all lone pairs of electrons and any partial charges. Explain the origin of these charges.
Suggest why this strong intermolecular force is not present between HI molecules.
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(7)

(b)     Crystals of sodium chloride and of diamond both have giant structures. Their melting points are 1074 K and 3827 K, respectively. State the type of structure present in each case and explain why the melting point of diamond is so high. 
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(4)
(Total 11 marks)
 
10.      (a)     An ammonium ion, made by the reaction between an ammonia molecule and a hydrogen ion, can be represented as shown in the diagram below.
			
(i)      Name the type of bond represented in the diagram by N—H
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(ii)     Name the type of bond represented in the diagram by N→H
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(iii)     In terms of electrons, explain why an arrow is used to represent this N→H bond.
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(iv)    In terms of electron pairs, explain why the bond angles in the NH4+ ion are all 109° 28’
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(7)

(b)     Define the term electronegativity.
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(2)
(c)     A bond between nitrogen and hydrogen can be represented as —
(i)      In this representation, what is the meaning of the symbol δ+ ?
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(ii)     From this bond representation, what can be deduced about the electronegativity of hydrogen relative to that of nitrogen?
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(2)
(Total 11 marks)
 
11.         The following table gives the melting points of some elements in Period 3.
 
Element	Na	Al	Si	P	S	
Melting point / K	371	933	1680	317	392	

(a)     State the type of structure shown by a crystal of silicon.
Explain why the melting point of silicon is very high.
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(3)
(b)     State the type of structure shown by crystals of sulfur and phosphorus.
Explain why the melting point of sulfur is higher than the melting point of phosphorus.
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(3)

(c)     Draw a diagram to show how the particles are arranged in aluminium and explain why aluminium is malleable.
(You should show a minimum of six aluminium particles arranged in two dimensions.)
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(3)
 (Total 9 marks)

12.	In 2009 a new material called graphane was discovered. The diagram shows part of a model of the structure of graphane. Each carbon atom is bonded to three other carbon atoms and to one hydrogen atom.

(a)     Deduce the type of crystal structure shown by graphane.
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(1)
(b)     State how two carbon atoms form a carbon–carbon bond in graphane.
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(1)
(c)     Suggest why graphane does not conduct electricity.
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(1)
(d)     Deduce the empirical formula of graphane.
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(1)
(Total 4 marks)

13.	Which one of the following is the most likely value for the bond angle α shown in the diagram of SF4 below?
 
A       118°
B       101°
C       90°
D       88°
(Total 1 mark)