Electrons, Bonding & Structure (OCR A Level Chemistry)

Exam Questions

3 hours39 questions
1a3 marks

This question is about how electrons are arranged inside the atom.

State the maximum number of electrons that can be held in each of the first three shells of an atom.

1b3 marks

From the second shell onwards, p-sub-shells exist. 

State how many orbitals there are in a p-sub-shell and how the electrons are arranged if this sub-shell is full.

1c1 mark

State why the 2s orbitals are filled before the 2p orbitals.

1d1 mark

Write the full electronic configuration of the Period 2 element, fluorine, Z = 9.

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2a1 mark

This question is about the Group 1 and Group 2 elements. 

The Group 1 and Group 2 metals are also known as s-block elements.

Explain this statement.

2b1 mark

Write the full electronic configuration of the sodium ion, Na+.

2c2 marks

Sodium ions and chloride ions form a giant ionic lattice in solid form. Sodium ions are smaller than chloride ions. 

Complete the diagram to show the location of the ions in the lattice of solid sodium chloride.

 

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2d2 marks

Explain the strength of the ionic bond in sodium chloride.

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3a2 marks

This question is about the ionic compound magnesium fluoride.

Magnesium forms a stable ion of Mg2+

i)
Which noble gas has the same electronic structure as Mg2+?

[1]

ii)
Write the electronic structure of the magnesium ion, Mg2+, in full.

[1]

3b2 marks

Magnesium reacts with fluorine to produce solid magnesium fluoride salt, MgF2

Draw dot-and-cross diagrams for the magnesium ion, Mg2+, and the fluoride ion, F-.

3c3 marks

Predict the electrical conductivity of magnesium fluoride in each of the following states:

 
State Electrical conductivity (Y / N)
Solid  
Liquid  
Aqueous  

 

3d2 marks

Explain why it is easier to use aqueous MgF2 than molten MgF2 in a laboratory setting.

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4a2 marks

This question is about covalent compounds.

Define a covalent bond.

4b2 marks

Oxygen can form single bonds with hydrogen across a number of compounds such as water, H2O, and methanol, CH3OH. 

The average bond enthalpy of an O-H bond is 463 kJ mol-1

Predict, with a reason, whether the enthalpy of the O-H bond in both H2O and CH3OH will be 463 kJ mol-1.

 
4c2 marks

Complete the dot-and-cross diagram of methanol, CH3OH. 

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4d1 mark

Methanol, CH3OH, can be oxidised to methanal, CH2O, and further oxidised to the methanoic acid, HCOOH. 

Methanoic acid contains a carbonyl bond, C=O, as well as a single carbon oxygen bond, C–O. 

State how the bond enthalpy of the C=O will compare to the bond enthalpy of the C–O.

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5a1 mark

A number of molecules can form dative covalent bonds.

Define what makes a dative covalent bond.

5b2 marks

Water molecules can form a dative covalent bond with a hydrogen ion, H+, to form the hydroxonium ion, H3O+

Draw a dot-and-cross diagram of H3O+

5c1 mark

Water is amphoteric and can also act as an acid and donate an H+ to another molecule, leaving an OH- ion behind.

One such example is the reversible reaction of water with ammonia, NH3, to form ammonium hydroxide.

Write a balanced equation for this reaction.

5d2 marks

State the number and type of covalent bonds present in the ammonium ion, NH4+.

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1a2 marks

Potassium and oxygen can react to form the ionic compound potassium oxide.

Write the full electron configuration for the potassium and oxygen atoms.

1b3 marks

Electrons are arranged in energy levels. The incomplete diagram below for the electrons in an oxygen atom shows just the two electrons in the 1s level.


Oxygen energy levels blank

Complete the diagram by populating the energy levels and adding labels for the sub-shells.

1c1 mark

Explain how ionic bonding holds the particles together in an ionic compound.

1d2 marks

Draw a dot-and-cross diagram to show the bonding in potassium oxide, K2O. Show outer electrons only.

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2a1 mark

The melting and boiling points of lithium and some lithium halides are shown below:

  Melting point / oC Boiling point / oC
Lithium 180 1342
Lithium bromide 550 1300
Lithium chloride 605 1382
Lithium fluoride 845 1676
Lithium iodide 469 1171

Identify the pattern, if any, in the melting and boiling points of the lithium halides. 

2b5 marks

Two students, A and B, are comparing the properties of lithium and lithium chloride.

Student A states that both lithium and lithium chloride will conduct electricity, but Student B states that only lithium will conduct electricity. 

State whether Student A, Student B, or neither student is correct. Explain your answer.

2c5 marks

Students A and B went on to discuss the solubility of lithium and the lithium halides in water.

Student A states that both lithium and all of the lithium halides will be soluble in water, but Student B states that only lithium bromide and lithium iodide will be soluble in water.

State which student, if any, is correct. Explain your answer. 

2d3 marks

Describe the bonding process that forms lithium halides, with respect to electrons.

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3a3 marks

Phosphorous trichloride, PCl3, bonds covalently.

Draw a dot-and-cross diagram to show the bonding in PCl3. Show the outer electrons only.

3b4 marks

Compare the bonding in phosphorous trichloride and ammonia.

3c2 marks

Boron trifluoride reacts with ammonia to form the trifluoroborane-ammonia complex.

Describe the type of bond that forms between the boron trifluoride and ammonia molecules.

3d2 marks

Draw a displayed formula showing the bonding for the trifluoroborane-ammonia complex, F3BNH3.

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4a2 marks

Combustion of carbon compounds is responsible for global warming, breathing and respiratory problems.

Write balanced symbol equations to show the complete and incomplete combustion of propane, C3H8.

4b2 marks

Draw a dot-and-cross diagram for a carbon dioxide molecule.

4c3 marks

Draw a dot-and-cross diagram for carbon monoxide.

4d3 marks

State the number of lone pairs and different types of bond in a carbon monoxide molecule.

4e1 mark

The average bond enthalpy for the carbon-oxygen bond is shown.

Molecule Bond enthalpy/ kJ mol-1 
Carbon monoxide  + 1077
Carbon dioxide + 805

Explain why the average bond enthalpy value for the carbon-oxygen bond found in carbon monoxide is higher than the carbon dioxide value.

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5a1 mark

The displayed formula of a carbonate ion, CO32-, is shown below.

carbonate-ion-displayed-formula

Draw the dot-and-cross diagram for the carbonate ion.

5b1 mark

The nitrate, NO3-, ion is a polyatomic ion containing one single covalent bond, one double covalent bond and one dative covalent bond.

Draw the displayed formula of the nitrate ion.

5c2 marks

When magnesium oxide is added to warm dilute nitric acid, a reaction takes place forming a solution containing ions.

Write an equation for this reaction, including state symbols.

5d2 marks

Solid magnesium oxide does not conduct electricity. When magnesium oxide reacts with dilute nitric acid, the solution formed does conduct electricity.

Explain the difference in the electrical conductivity of the magnesium oxide and the solution formed. 

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1a6 marks

The Periodic Table is shaped by patterns in physical and chemical properties. The electronic configuration is key to understanding these patterns.

Describe how the shape of the Periodic Table is linked to the electronic structure, with particular reference to sub-shell structure.

1b2 marks

Elements can be identified using their location within the Periodic Table. 

i)
Identify the name and block of the sixth element in the fourth period.

[1]

ii)
Write out the full electronic configuration of this element.

[1]

1c3 marks

Suggest why there are three possible p-sub-shells but only one possible s-sub-shell in an atom.

1d3 marks

Justify why hydrogen is positioned in the middle of the Periodic Table and not as the first element in Group 1.

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2a2 marks

This question is about ionic bonding and structure.

The strength of ionic bonding in different compounds can be compared by using the amount of energy required to separate the ions, as shown in Table 1.

Table 1

Fluoride compound Amount of energy needed to separate the ions/ kJ mol-1
LiF 1031
NaF 787
MgF2 2962

Using the data in Table 1, explain how changing the cation affects the bond strength in an ionic compound.

2b3 marks

Coal often contains traces of iron(II) disulfide, FeS2, also known as pyrite or 'fool's gold'.

FeS2 is an ionic compound made of Fe2+ and S22- ions.

i)
Describe the bonding in an S22- ion.

[1]

ii)
Draw a dot-and-cross diagram for FeS2. Show outer shell electrons only.

[2]

2c5 marks

Silver chloride, AgCl, is a chloride compound that has uses in photography films as well as having antiseptic properties. Silver chloride also has a high melting point. 

i)
Draw a diagram of a silver chloride lattice to show the arrangement of the ions.

[2]

ii)
Explain, with reference to structure and bonding, why silver chloride has such a high melting point.

[3]

2d4 marks

Aluminium chloride, Al2Cl6, does not conduct electricity when molten but aluminium oxide, Al2O3, does. Explain this in terms of the structure and bonding of the two compounds.

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3a2 marks

The nitrate (V) ion, NO3-, is a polyatomic ion, bonded by covalent bonds. 

The three oxygen atoms are bonded by one single covalent bond, one double covalent bond and one dative covalent bond.

Draw the Lewis structure for NO3-

3b2 marks

An ionic compound has the empirical formula H4N2O3

Suggest the formulae of the ions present in this compound.

3c2 marks

Cyanide is a fast-acting chemical, which can be found in various forms and can have toxic effects on the body.

Draw the dot-and-cross structure for a CN- ion. 

Show the outer electrons only.

3d2 marks

Compare the average bond enthalpy in the cyanide ion to the average bond enthalpy of the C-N bond in methylamine, CH3NH2. Explain your answer.

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4a2 marks

Ethyne, C2H2, is a hydrocarbon which can be used in the artificial ripening of fruits. It can be synthesised by a two-step process.

Firstly, calcium oxide and coal react together to form calcium carbide (CaC2) and carbon monoxide. The second step involves calcium carbide reacting with water to form calcium hydroxide and ethyne, C2H2.

Write two equations to represent the two-step process forming ethyne, C2H2. State symbols are not required.

4b1 mark

Draw a dot-and-cross diagram of the ethyne molecule, C2H2.

4c4 marks

Describe the bonding in calcium carbide, CaC2.

4d3 marks

Compare and contrast the expected physical properties of calcium oxide and calcium carbide.

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5a4 marks

Oxides of elements in the same period of the Periodic Table can have significantly different properties. 

The compounds SO2 and MgO are both oxides but with different melting points as shown below.

Compound Melting point / ℃
SO2 -72
MgO 2852

Describe the bonding in, and the structure of, SO2 and MgO and explain the difference in their melting points.

5b3 marks

Predict how the melting point of sodium chloride will compare the that of magnesium oxide and justify your answer.

5c3 marks

SO2 can be represented by more than one valid dot-and-cross diagram. One way of drawing it involves a single dative bond between the sulfur and one of the oxygens.

Draw this dot-and-cross diagram of SO2 and identify the types of bonds present.

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