COVALENT BONDING PRACTICE
Q1. The diagram represents a particle of methane.
(a)
What is the formula of methane? ...............................................................................
(1)
(b)
Choose a word from the box to answer the question.
atom
ion
molecule
Which of the words best describes the methane particle shown in the diagram?
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(1)
(c)
Choose a word from the box to answer the question.
covalent
ionic
metallic
What is the type of bonding shown in the diagram?
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(1)
(Total 3 marks)
Q2. This barbecue burns propane gas.
The structure of propane is shown below.
(a)
Complete the diagram to show how the outer energy level (shell) electrons of hydrogen
and carbon are arranged in a molecule of propane.
(1)
(b)
The graph shows how the vapour pressure of propane changes with temperature.
The vapour pressure of a liquid is the pressure of the vapour above the liquid.
(i)
Describe, as fully as you can, how the vapour pressure of propane changes with
temperature.
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(2)
(ii)
The boiling point of a liquid is the temperature at which its vapour pressure is equal
to the air pressure above the liquid.
Use the graph to find the boiling point of propane when the air pressure is 100
kilopascals.
Boiling point ................................................... °C
(1)
(c)
Explain, in terms of molecules, why propane has a low boiling point.
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(2)
(Total 6 marks)
Q3. The diagrams represent the atomic structures of two gases, hydrogen and helium.
Hydrogen gas is made up of diatomic molecules (molecules with two atoms).
Helium gas exists as single atoms.
(i)
How is a molecule of hydrogen formed from two hydrogen atoms?
(You may use a diagram as part of your answer)
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(2)
(ii)
Why does helium exist only as single atoms?
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(2)
(b)
Hydrogen combines with carbon to form methane.
Each molecule contains four hydrogen atoms strongly bonded to a carbon atom.
Explain why methane has a low boiling point.
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(2)
(Total 6 marks)
Q4. The diagram shows one molecule of the compound ammonia.
Write down everything that the diagram tells you about each molecule of ammonia.
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(Total 4 marks)
Q5. The questions which follow refer to the element hydrogen.
(a)
Draw a diagram to show the bonding in one molecule of hydrogen.
(2)
(b)
The table gives information about two compounds which contain hydrogen.
Use the information in the table to explain why it is difficult to classify hydrogen as a metal
or a non metal.
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(4)
(Total 6 marks)
Q6..
Chlorine will combine with the non-metal element, carbon, to form this molecular
compound.
(a)
What is the type of bond in this molecule?
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(1)
(b)
Explain how these bonds are formed. (You may use a diagram).
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(2)
(Total 3 marks)
Q7. Complete the drawing to show the electron structure of a hydrogen fluoride molecule. Draw
electrons as dots or crosses.
(1)
(ii)
Explain why hydrogen fluoride is a gas at room temperature.
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(2)
(Total 3 marks)
Q8. Sulphur hexafluoride is a colourless, odourless, non-flammable gas, which is insoluble in water
and extremely unreactive. It is used as an insulator in high voltage transformers and switchgear.
The diagram below represents a molecule of sulphur hexafluoride.
(a)
What type of chemical bond holds the sulphur and fluorine atoms together in sulphur
hexafluoride molecules?
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(1)
(b)
Explain why sulphur hexafluoride has a low boiling point.
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(2)
(c)
Explain how three of the properties of sulphur hexafluoride make it suitable for use as an
insulator inside electrical transformers.
Property 1: ..................................................................................................................
Explanation: ...............................................................................................................
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Property 2: ..................................................................................................................
Explanation: ...............................................................................................................
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Property 3: ..................................................................................................................
Explanation: ...............................................................................................................
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(3)
(Total 6 marks)
MS
Q1.
CH4
4 should be below halfway up H / tail of 4 below the dotted line
1
(b)
molecule
1
(c)
covalent
Q2. (a)
allow all dots
or
all crosses
or
combination
or
all e / e–
or –
or other suitable symbols
centre of symbols must be on or inside overlapping
areas within reason
1
(b)
(i)
any two from:
•
no change initially or stays constant at the beginning
•
increase
•
slowly at first and then more rapidly
accept converse arguments
allow vapour pressure is 0 at any temperature <–100oC for 1 mark
accept positive correlation
accept explanation based on kinetic theory eg particles have more
kinetic energy
allow reasonable attempt at using numbers
2
(ii)
–44 (using graph) accept –43 to –45
1
(c)
•
intermolecular forces / bonds or forces / bonds between molecules
1
•
bonds / forces are weak
covalent bonds are weak = 0 marks
if they do not gain either of the marks on the left then allow simple
covalent / molecular / made of small molecules for 1 mark
1
[6]
Q3. (a)
(i)
idea that
•
two hydrogen atoms share one pair of electrons
•
linked by a covalent bond
•
each then has two outer electrons / a full outer shell / two
•
electrons in the highest (occupied) energy level
(2 marks may be awarded for a correct electron diagram i.e. with electrons on
boundary of or within marked area).
any two for 1 mark each
2
(ii)
idea that
•
helium atoms do not give / take / share electrons / react
•
because the (outer) shell / orbit is full
or
•
highest (occupied) energy level is full
(but not just “contains two electrons”)
for 1 mark each
2
(b)
idea that
•
the (attractive) forces between molecules are weak
(not bonds between atoms)
•
so little energy is required / it is easy for molecules to escape from the liquid*
/ escape from other molecules*
(allow evaporate / change into a gas)
for 1 mark each
2
[6]
Q4. idea that
•
contains nitrogen atoms
•
contains hydrogen atoms
•
atoms are chemically bonded
•
ratio of one nitrogen to three hydrogen (atoms) formula of ammonia is NH3
for 1 mark each
NOT linked/joined
Q5. correct representation of 1 atom of hydrogen e.g.
gains 1 mark
but correct representation of 1 molecule of hydrogen e.g. or H-H
gains 2 marks
2
(b)
idea that:
hydrogen/metals form positive ions/lose electrons
gains 1 mark
but hydrogen and the metals form positive ions/lose electrons
gains 2 marks
hydrogen/non-metals form covalent bonds/share electrons
gains 1 mark
but hydrogen and the non-metals form covalent bonds/share electrons
gains 2 marks
4
[6]
Q6. covalent bonds
for 1 mark
1
(b)
any reference to shared electrons
gains 1 mark
but idea that bond is shared pair of electrons
gains 2 marks
2
[3]
Q7. 1
(ii)
weak forces
accept weak bonds
1
between molecules / intermolecular
reject intramolecular
1
[3]
Q8. covalent/description of covalent
for 1 mark
1
(b)
forces/bonds between the molecules/particles (not atoms) are weak
for 1 mark each
2
(c)
non-flammable so it will not burn etc.
extremely unreactive so it will not react with materials in the transformer,
does not conduct electricity so it can insulate the transformer
gas so it has freedom to move and insulate whole area
for 1 mark each
3
[6]