Syllabus Edition

First teaching 2023

First exams 2025

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The Covalent Model (HL IB Chemistry)

Exam Questions

10 hours149 questions
1a
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1 mark

Using Section 9 of the data booklet to state which of the following single covalent bonds is the most polar.

C-O C-H O-H

1b1 mark

Using Section 11 of the data booklet, list the following molecules in order of increasing bond length between the carbon atoms.

C2H6 C2H4 C2H2
1c1 mark

Using Section 12 of the data booklet, list the following molecules in order of decreasing bond strength between the carbon atoms.

C2H6 C2H4 C2H2
1d1 mark

CO contains three covalent bonds, one of which is a coordinate bond.

Describe how a coordinate bond arises in CO.

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2a2 marks

Calcium nitrate contains both covalent and ionic bonds.

State the formula of both ions present and the nature of the force between these ions.

2b1 mark

State the formula of the compound that boron forms with chlorine.

2c1 mark

Draw the Lewis structure for boron chloride.

2d1 mark

Explain why boron trichloride is able to form coordinate (covalent) bonds with other molecules. 

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3a2 marks

State the formula for benzene and draw the displayed structure.

3b1 mark

State the bond angle in the planar regular hexagon structure of benzene.

3c1 mark

Cyclohexene is an unsaturated hydrocarbon and can undergo hydrogenation as shown below.

3-8


When benzene undergoes the same reaction with three hydrogen molecules the 
expected enthalpy change of the reaction is lower than expected. 

State the expected value of the hydrogenation of benzene.

3d2 marks

Explain why the enthalpy value for the hydrogenation of benzene is lower than expected. 

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4a2 marks

Two types of covalent bond are sigma and pi bonds.

i)
Describe how a sigma (straight sigma) bond is formed

[1]

ii)
Describe how a pi (straight pi) bond is formed

[1]

4b2 marks

Describe the difference in the location of the electron dense regions in sigma (straight sigma) and pi (straight pi) bonds.

4c2 marks

Deduce the number of sigma (straight sigma) and pi (straight pi) bonds in methane, CH4.

4d2 marks

Deduce the number of sigma (straight sigma) and pi (straight pi) bonds in oxygen, O2.

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5a2 marks

Sulfur can form bonds with six fluorine atoms to form sulfur hexafluoride, SF6.

i)
How many electrons are in the outer shell of the sulfur in SF6?

[1]

ii)
State the minimum and maximum numbers of electrons possible in the outer shell of sulfur.

[1]

5b1 mark

Sulfur has no lone pairs when bonded to fluorines in SF6. Predict the molecular geometry of sulfur hexafluoride, SF6.

5c1 mark

State the F-S-F bond angles in SF6.

5d3 marks

Phosphorus pentafluoride, PF5, is also a molecule with an expanded octet around the central atom.

i)
Draw a Lewis (electron dot) structure for PF5

[1]

ii)
Predict the molecular geometry of PF5

[1]

iii)
State the F-P-F bond angle(s)

[1]

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6a2 marks

Although noble gases do not normally react, a few compounds are possible. One is xenon tetrafluoride.
Draw the Lewis structure (electron dot) for XeF4.

6b2 marks

Predict the molecular geometry and electron domain geometry for the XeF4 molecule.

6c2 marks

Predict and explain the F-Xe-F bond angle in XeF4

6d
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2 marks

The formal charge on an atom can be calculated by the following: 

FC = (Number of valence electrons) - ½(Number of bonding electrons) - (Number of non-bonding electrons)

Calculate the formal charge on the xenon and the fluorines in xenon tetrafluoride, XeF4.

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7a2 marks

Draw a Lewis (electron dot) structure for carbon dioxide, CO2.

7b2 marks

Predict the molecular geometry and the O-C-O bond angle in carbon dioxide, CO2.

7c2 marks

An alternative way to draw the carbon dioxide molecule is:

co2-resonance-lewis-structure-ib-hl-sq-14-1-4c

Identify the formal charge on each of the oxygen atoms.

7d2 marks

State which of the Lewis structures, that from part a) or part c), is preferable and explain your choice.

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8a2 marks

There are a number of different types of intermolecular force possible between molecules.

Which types of forces can be classified as 'van der Waals' forces?

8b2 marks

Methanol, CH3OH, is a small alcohol molecule that forms hydrogen bonds with water.

Sketch 2 different hydrogen bonding interactions between methanol and water.

8c4 marks

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

Identify the strongest type of intermolecular force between:

i)
Methanal molecules
[1]
ii)
Methanoic acid molecules
[1]
iii)
Water and methanal
[1]
iv)
Water and methanoic acid
[1]
8d3 marks

Methanoic acid reacts with sodium hydroxide to form sodium methanoate:

HCOOH + NaOH rightwards arrowHCOONa + H2O

Explain why sodium methanoate is a solid at room temperature and methanoic acid is a liquid.

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9a2 marks

Group 17 of the Periodic Table contain non-metals that are often referred to as the halogens.

Iodine, I2, is one of these halogens. At room temperature and pressure it exists as a grey-black solid.

Describe the bonding and forces present in I2 in the solid state.

9b2 marks

The state of the halogens changes down the group, with fluorine being a gas and astatine being a solid.

Explain why the melting point of the halogens increases down the group.

9c3 marks

The halogens are all diatomic covalent molecules.

Predict the most probable physical properties shown by all of the elements in Group 17.

9d3 marks

The halogens can also form interhalogen compounds, such as iodine monochloride, ICl.

Predict the state of iodine monochloride at room temperature and pressure, and explain your answer with reference to the intermolecular forces present.

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10a1 mark

State what is meant by the term delocalisation of electrons.

10b3 marks

Delocalisation is common in some types of organic molecule.
 

i)
Identify whether ethanoic acid, CH3COOH, has delocalised straight pi electrons.

[1]

ii)
Identify where the ethanoate ion, CH3COO-, has delocalised electrons.

[1]

iii)
Give a reason for your choices.

[1]

10c2 marks

Draw two resonance structures for the ethanoate ion, CH3COO-.

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11a1 mark

Benzene, C6H6, has two resonance structures. Draw skeletal formulae of these two structures.

11b2 marks

Benzene is commonly drawn in the following manner:

benzene-ib-hl-sq-14-2-2b

Explain what this represents and why this is a useful way to draw benzene.

11c2 marks

Some of the sigma bonds in benzene are formed from hybrid orbitals. The type of hybridisation present is sp2.

State which orbitals hybridise to form sp2 orbitals.

11d2 marks

The sp2 hybridized orbitals form sigma bonds in the benzene molecule. The delocalised electrons from pi bonds.
 

i)
Deduce the number of sigma (straight sigma) bonds in benzene.
[1]
ii)
Deduce the number of pi (straight pi) bonds in benzene.
[1]

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12a3 marks

Methane contains sp3 hybridised orbitals.

i)
Explain the formation of sp3 hybridised orbitals.

[2]

ii)
How many sp3 hybridised orbitals are present in methane?

[1]

12b4 marks

Ethyne, C2H2, is another hydrocarbon, in this case containing sp hybrid orbitals.

 
i)
Explain the formation of the sp hybrid orbitals in ethyne

[2]

ii)
Deduce the number of sp hybrid orbitals in a molecule of ethyne.
[1]
iii)
State if these sp hybrid bonds form sigma (σ) or pi (π) (bonds)

[1]

12c2 marks

Explain, using the concept of hybridisation, how the triple bond in ethyne, C2H2, forms.

12d2 marks

Ethanenitrile, CH3CN, is an organic molecule with a tetrahedral molecular geometry around one carbon and a linear molecular geometry around the other carbon. The structure is shown below:

ethanenitrile-ib-hl-sq-14-2-q4d

i)
Identify how many sp3 hybrid orbitals are present in this molecule.

[1]

ii)
Identify how many sp hybrid orbitals are present in this molecule.

[1]

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13a3 marks

Yellow phosphorus reacts with chlorine to form phosphorus trichloride, PCl3.

i)
Draw the Lewis (electron dot) structure of phosphorus trichloride.
[1]
ii)
Predict the Cl-P-Cl bond angle and molecular geometry of the phosphorus trichoride molecule.
[2]
13b4 marks

Phosphorus trichloride, PCl3, can form a co-ordinate bond with a hydrogen ion to form HPCl3+.

i)
Draw the Lewis (electron dot) structure of HPCl3+.
[2]
ii)
Predict the bond angle and molecular geometry of HPCl3+.
[2]
13c4 marks

BCl3 has three electron domains in a trigonal planar structure.

BCl3 is not a polar molecule, but PCl3 is.

Explain this difference using section 9 of the Data booklet.

13d2 marks

PCl4+ has the same electron domain geometry as HPCl3+.

Explain why PCl4+ is not a polar molecule.

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14a3 marks

This question is about the geometry of a number of common molecules.

simple-molecules

i)
Which molecule(s) has/ have tetrahedral structures with respect to the electron domain geometry?
[1]
ii)
What is the molecular geometry of CO2?
[1]
iii)
Draw the 3D representation of ammonia, NH3.
[1]

14b3 marks

Estimate the H-O-H bond angle in water, H2O, using VSEPR theory.

Explain your answer.

14c3 marks

Suggest a way in which the bond angle in ammonia / NH3 could become 109.5o and explain your answer.

14d3 marks

Ozone, O3, is another simple molecule which has the following structure:

4-2-ib-sl-sq-easy-q2d-ozone-display-formula-with-lone-pairs

i)
Estimate the O-O-O bond angle in ozone using VSEPR theory.
[1]
ii)
Explain why the actual bond lengths present in ozone are equal.
[2]

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15a4 marks

Carbon has three naturally occurring allotropes; diamond, graphite and buckminsterfullerene, C60.

State how many atoms each carbon is directly bonded to in each of the allotropes, explaining any differences.

15b3 marks

Describe the differences in the structures of the three allotropes of carbon.

15c4 marks

Describe and explain the differences in electrical conductivity between the three allotropes of carbon.

15d2 marks

Graphene can be made from graphite.

Describe a similarity and difference between these two structures.

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16a4 marks

Silicon and carbon are in the same group of the Periodic Table. They both form covalent bonds.

4-2-ib-sl-sq-easy-q4a-silicon-dioxide

O=C=O (carbon dioxide)

Both silicon and carbon form dioxides, but silicon dioxide has a melting point of 1710 oC whilst carbon dioxide has a melting point of -78 oC.

Explain this difference with reference to the structure and bonding present in each dioxide.

16b3 marks

How many oxygen atoms are bonded to each carbon and to each silicon?

Explain how this links to the formula of each compound.

16c2 marks

Predict the O-C-O and O-Si-O bond angles respectively in CO2 and in SiO2.

16d4 marks
Predict and explain the solubility of both SiO2 and CO2 in water.

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1a6 marks

For each of the molecules below, draw the Lewis (electron dot) structure and use the valence shell electron pair repulsion theory (VSEPR) to predict the shape of each molecule.

Oxygen difluoride (OF2), phosphorus trifluoride, (PF3) and boron trichloride, (BCl3).

1b2 marks

Crystalline ionic compounds do not conduct electricity. 

State and explain in which states ionic compounds conduct electricity.

1c3 marks

The melting point of sodium chloride, NaCl, is 801° C. 

Explain, with reference to structure and bonding, why sodium chloride melts at such a high temperature.

1d2 marks

We can use electronegativity values to deduce whether a compound is likely to be ionic or covalent.

Use Section 9 of the Data Booklet to state and explain whether each of the following compounds are ionic or covalent:

   ICl

   SrCl2

   RbI

   HI

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2a2 marks

Diimide, N2H2, is a useful reagent in organic synthesis and can be made by the thermal decomposition of azodicarboxylic acid.

N(COOH)2 (g) → N2H2 (g) + 2CO2 (g) 

Another useful compound of nitrogen is hydrazine, N2H4. 

Draw Lewis (electron dot) structures for diimide and hydrazine.

2b2 marks

Deduce the molecular geometry of diimide and estimate its H-N-N bond angle.

2c3 marks

List, with an explanation, the three compounds in order of increasing carbon to oxygen bond length (shortest first). 

               H3COCH3              CO              CO2       

2d2 marks

Use Section 9 of the Data Booklet to predict which bond in each of the following pairs is more polar:

i)         C–H or C–Cl

[1]

ii)        Si–Li or Si–Cl

[1]

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3a3 marks

Three types of covalent bonds are present in the molecules in the following equation. 

            2C2H2 (g) + 5O2 (g) → 4CO2 (g) + 2H2O (l) 

Identify one bond in these molecules that is correctly described by the following: 

i)       A polar single bond. 

[1]

ii)       A non-polar double bond. 

[1]

iii)      A non-polar triple bond.

[1]

3b2 marks

Explain which of the bonds in part (a) is the shortest.

3c3 marks

Table 1 shows the carbon-carbon bond enthalpy values for three different hydrocarbons. 

Table 1 

Hydrocarbon

C2H6

C2H4

C2H2

Bond enthalpy /

kJ mol-1

346

614

839

Explain the difference in carbon-carbon bond enthalpy values for the three hydrocarbons.

3d2 marks

We can use electronegativity values to deduce whether a compound is likely to be pure covalent (non-polar) or polar covalent. 

Use Section 9 of the Data Booklet to state and explain whether each of the following covalent compounds is polar or non-polar:

H2       HCl       CO

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4a2 marks

Ammonia, NH3, is a chemical that is key in the manufacture of certain fertilisers and cleaning products.

An ammonia molecule will react with an H+ ion, to form the ammonium ion, NH4+.

Draw a Lewis (electron dot) diagram to show the bonding in the ammonium ion and name the type of bond formed between the ammonia molecule and the hydrogen ion. 

4b3 marks

Lewis (electron dot diagrams) are used to show the electron arrangement in the valence shells of covalently bonded molecules.

Draw Lewis diagrams for the following molecules:

i)         Hydrogen cyanide.

[1]

ii)        Carbon dioxide.

[1]

iii)        Boron trifluoride.

[1]

4c2 marks

Using your answer to part (b), identify and explain the species that is likely to form a coordinate covalent bond.

4d3 marks

Using your answer to part (c), Explain, with the help of a diagram, the covalent bond formed between the species in part (c) and ammonia.

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5a2 marks

Benzene is an aromatic hydrocarbon which is often drawn as Figure 1.

Discuss the physical evidence that justifies this structure for benzene.

Figure 1

10-1-ib-chemistry-sq-q5a-medium

5b3 marks

Benzene and cyclohexene are both unsaturated molecules, but cyclohexene reacts with bromine water and benzene does not.

i)

State the meaning of the terms saturated and unsaturated as applied to organic molecules. 

[1]

ii)
Explain this difference in reactivity and write an equation for the reaction between cyclohexene and bromine. 
[2]
5c3 marks

Table 1 below shows the enthalpy changes for the hydrogenation of cyclohexene, benzene, and the theoretical molecule 1,3,5-cyclohexatriene.

Table 1

Compound

Enthalpy of hydrogenation

Cyclohexene, C6H10

-120

Benzene, C6H6

-208

1,3,5-cyclohexatriene, C6H6

?

 

The equations for the hydrogenation reactions are:

Cyclohexene               C6H10 + H2 ⭢ C6H12

Benzene                      C6H6 + 3H2 ⭢ C6H12

i)
Use the data in Table 1 to determine the enthalpy of hydrogenation of the theoretical molecule 1,3,5-cyclohexatriene. 
[1]
ii)
Discuss the difference between the enthalpy of hydrogenation of benzene and of 1,3,5-cyclohexatriene. 
[2]
5d2 marks

An unknown aromatic compound has the molecular formula C8H8O2.

Deduce the structural formula of two isomers of this compound which contain an ester group.

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6a2 marks

Phosphorus tribromide and sulfur tetrafluoride are two colourless compounds which both react with water to form toxic products. 

Deduce the Lewis (electron dot) structure of both molecules.

6b2 marks

Predict the shapes of the two molecules of phosphorus tribromide and sulfur tetrafluoride

6c2 marks

Explain why both phosphorus tribromide and sulfur tetrafluoride are polar.

6d2 marks
Compare the formation of a sigma (σ) and a pi (π) bond between two carbon atoms in a molecule.

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7a2 marks

But-2-ene-1,4-dioic acid exists as both cis and trans isomers. The cis isomer is shown below:

q2a_14-1_ib_hl_medium_sq

Describe the type of covalent bond between carbon and hydrogen in the molecule shown above and how it is formed.

7b2 marks

Identify how many sigma bonds and how many pi (π) bonds are present in cis but-2-ene-1,4-dioic acid.

7c3 marks
Draw the Lewis structures, predict the shape and deduce the bond angles for xenon tetrafluoride.
7d3 marks
Compare the polarity of xenon tetrafluoride with chlorine trifluoride.

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8a2 marks

Carbon dioxide can be represented by at least two resonance structures, I and II.

q3a_14-1_ib_hl_medium_sq

Calculate the formal charge on each oxygen atom in the two structures.

Structure

I

II

O atom labelled (1)

 

 

O atom labelled (2)

 

 

8b2 marks

Deduce, giving a reason, the more likely resonance structure from part a)

8c3 marks

Nitrous oxide can be represented by different Lewis (electron dot) structures. 

Deduce the formal charge (FC) of the nitrogen and oxygen atoms in three of these Lewis (electron dot) structures, A, B and C, represented below. 

LHS: atom on the left-hand side; RHS: atom on the right-hand side

 

Lewis (electron dot) structure

FC of O on LHS

FC of central N

FC of N on RHS

A

q3c1_14-1_ib_hl_medium_sq      

B

q3c2_ib_hl_medium_sq      

C

q3c_14-1_ib_hl_medium_sq      
8d3 marks

Based on the formal charges assigned in part c), deduce which Lewis (electron dot) structure of N2O (A, B, or C) is preferred.

Explain another factor that also must be taken into account in determining the preferred structure.

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9a2 marks

Use the concept of formal charge to explain why BF3 is an exception to the octet rule.

9b2 marks

Compounds containing two different halogen atoms bonded together are called interhalogen compounds. They are interesting because they contain halogen atoms in unusual oxidation states. One such compound is BrF3

Deduce the electron domain geometry and molecular geometry of BrF3.

9c2 marks

Give the approximate bond angle(s) and a valid Lewis (electron dot) structure for BrF3

9d2 marks

Explain why bromine trifluoride, BrF3 has its lone pairs of electrons located in equatorial positions. 

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10a2 marks

Draw two different Lewis (electron dot) structures for SO42–, one of which obeys the octet rule for all its atoms, the other which has an octet for S expanded to 12 electrons. 

10b2 marks

Explain which of the two SO42– structures is preferred using formal charges.

10c2 marks

Consider the molecule shown below.

q5c_14-1_ib_hl_medium_sq

Identify the number of sigma and pi bonds in this molecule.

10d3 marks

One of the intermediates in the reaction between nitrogen monoxide and hydrogen is dinitrogen monoxide, N2O. This can be represented by the resonance structures belowq5d_14-1_ib_hl_medium_sq

 Analyse the bonding in dinitrogen monoxide in terms of sigma and pi bonds.

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11a2 marks

Based on the type of intermolecular force present, explain why butan-1-ol has a higher boiling point than butanal.

11b2 marks

Ethane, C2H6, and disilane, Si2H6, are both hydrides of Group 4 elements with similar structures but different chemical properties.

Explain why disilane has a higher boiling point than ethane.

11c3 marks

Put the following molecules in order of increasing boiling point and explain your choice:

CH3CHO

CH3CH2OH

CH3CH2CH3

11d4 marks

Based on the type of intermolecular force present, explain the difference in solubility in water between ethane and ethanol.

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12a3 marks

The melting points of some Group 1 elements are listed in Table 1.

Table 1

 

Na

K

Rb

Melting point / °C

98

63

 

 

Predict, with a reason, the melting point of Rb.

12b2 marks

Explain why ammonia, NH3, is a gas at room temperature. 

12c3 marks

Phosphine (IUPAC name phosphane) is a hydride of phosphorus, with the formula PH3. Phosphine has a much greater molar mass than ammonia.

Explain why phosphine has a significantly lower boiling point than ammonia.

12d2 marks

Identify the type of interaction that must be overcome when liquid hydrazine, N2H4, vaporizes. Suggest, with a reason, whether hydrazine has a lower or higher boiling point than diimide, N2H2.

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13a4 marks

Cyclohexane C6H12 has a puckered, non-planar shape whereas benzene C6H6 is planar. 

Explain this difference by making reference to the C–C–C bond angles and the type of hybridisation of carbon in each molecule.

13b4 marks

Urea, CO(NH2)2, is present in solution in animal urine. 

What is the hybridisation of C and N in the molecule, and what are the approximate bond angles?

13c4 marks

Describe the hybridisation of the carbon atom in methane and explain how the concept of hybridisation can be used to explain the shape of the methane molecule

13d1 mark

A molecule of ethanol is shown below.

q2d_14-2_ib_hl_medium_sq

Deduce the hybridisation of the carbon atom marked in the diagram below.

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14a1 mark

Carbonation is the process of increasing the concentration of carbonate ions in water to produce carbonated drinks.

Identify the hybridisation of the central carbon atom.

14b3 marks

Explain, with the use of diagrams, how there are three valid structures for the carbonate ion.

14c3 marks

Describe the distribution of pi (π) electrons and explain how this can account for the structure and stability of the carbonate ion, CO32–.

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15a3 marks

Explain how the concept of hybridisation can be used to explain the triple bond present in propyne.

15b1 mark

Consider the molecule below which contains both sigma and pi bonds.

q4b_14-2_medium_ib_hl_sq

 How many carbon atoms exhibit sp2 hybridisation in this molecule?

15c3 marks

Deduce the hybridisation shown by the nitrogen atoms in NF4+, N2H2 and N2H4.

   NF4+ N2H2 N2H4
Hybridisation      

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16a2 marks

Draw the structure of silicon dioxide and state the type of bonding present.

16b3 marks

Describe the similarities and differences you would expect in the properties of silicon and diamond.

16c4 marks

The boiling point of diamond is 3550 ℃, but for carbon dioxide it is -78.5 ℃. Both are covalent substances. 

Explain this difference with reference to structure and bonding.

16d2 marks

Silicon dioxide has a similar name to carbon dioxide, but its boiling point is 2230 ℃. 

Briefly outline the reason for this difference.

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17a2 marks

In 1996 the Nobel prize in Chemistry was awarded for the discovery of a new carbon allotrope, known as fullerenes. 

Outline the structure of buckminsterfullerene.

17b5 marks

Like carbon dioxide, graphite is also a covalent substance, but it is a solid at room  temperature. Graphite has a melting point of around 3600 oC.           

Describe the structure and bonding of graphite and explain why it has such a high melting point.

17c4 marks

Graphite is made purely of carbon, a non-metal, yet it conducts electricity.
Diamond, which is also made purely of carbon, cannot conduct electricity. 

i)
Explain this difference in electrical conductivity between graphite and diamond. 

[3]

ii)
Give one other difference in the properties of graphite and diamond.

[1]

17d4 marks

Graphite is soft and so is used as a lubricant, whereas diamond is hard and so is used in many cutting tools. Both are giant covalent structures.

Explain this difference with reference to structure and bonding.

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18a3 marks

The Valence Shell Electron Pair Repulsion Theory (VSEPR) is used to predict the shapes of many chemical molecules.

Describe the main features of the VSEPR theory for predicting shapes of molecules.

18b3 marks

State and explain the bond angle F-O-F in OF2.

18c3 marks

Deduce whether each of the three molecules oxygen difluoride, OF2, phosphorus trifluoride, PF3, and boron trichloride, BCl3, are polar or non-polar.

Give a reason in each case.

18d4 marks

Predict and explain the shapes and bond angles of the following molecules:

i)        BF3 

[2]

ii)       NBr3 

[2]

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19a5 marks

Ethene, C2H4, and hydrazine, N2H4, are hydrides of adjacent elements in the periodic table. 

State and explain the H一C一H bond angle in ethene and the H一N一H bond angle in hydrazine.

19b2 marks

Hydrazine can be oxidised to form diimide, which is a useful compound used in organic synthesis. 

Deduce the molecular geometry of diimide, N2H2, and estimate its H–N–N bond angle.

19c4 marks

Explain whether ethene and hydrazine are polar or non-polar.

19d1 mark

Hydrazine forms a cation with an ethane-like structure called hydrazinediium,  N2H62+.

Predict the value of the H–N–H bond angle in N2H62+.

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20a2 marks

Draw the resonance structures for the following ions:

i)        Methanoate, HCOO-.

[1]

ii)       Nitrate(III), NO2.

[1]

20b3 marks

Deduce the resonance structures of the carbonate ion, giving the shape and the oxygen-carbon-oxygen bond angle.

20c3 marks

In December 2010, researchers in Sweden announced the synthesis of N,N–dinitronitramide, N(NO2)3. They speculated that this compound, more commonly called trinitramide, may have significant potential as an environmentally friendly rocket fuel oxidant. 

Deduce the N–N–N bond angle in trinitramide and explain your reasoning.

20d2 marks

Predict, with an explanation, the polarity of the trinitramide molecule.

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1a3 marks

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

Silver chloride has a high melting point and a structure similar to sodium fluoride.

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

1b1 mark

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

Draw the Lewis structure for a CN- ion. 

Show the outer electrons only.

1c3 marks

Ammonia, NH3, and boron trifluoride, BF3, react together to form NH3BF3. Each of the molecules NH3 and BF3 have different features of its electronic structure which allows them to bond together.

Explain how the two molecules bond together and what type of bond is formed between NH3 and BF3.

You may use a labelled diagram to help you.

1d4 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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2a1 mark

State why magnesium and oxygen form an ionic compound while carbon and oxygen form a covalent compound.

2b2 marks

Explain why the melting point of phosphorus(V) oxide is lower than that of sodium oxide in terms of their bonding and structure.

2c2 marks

N, N–dinitronitramide N(NO2)3, also known as trinitramide, has been identified as a potentially more environmentally friendly rocket fuel oxidant.

Using Section 11 of the data booklet, outline how the length of the bond between nitrogen atoms in trinitramide compares with the bond between nitrogen atoms in nitrogen gas, N2.

2d2 marks

Describe the bonding within the carbon monoxide molecule.

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3a2 marks

Draw a diagram to show the resonance structure in a molecule of benzene. 

3b
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3 marks

The energy change for hydrogenation of cyclohexene is -120 kJ mol-1. However, when benzene undergoes hydrogenation, the energy change is 152 kJ mol-1 less than expected. 


Use this data to explain the relative stabilities of benzene and the theoretical
cyclohexa-1,3,5-triene molecule. 

3c4 marks
With reference to bonding and hybridisation, describe the structure of benzene.

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4a4 marks

Deduce the number of possible resonance structures for the carbonate ion, CO32-, and draw two of them.

Include the formal charges for each oxygen.

4b2 marks

An alternative structure for the carbonate ion is proposed:

ib-hl-sq-14-1-h-proposed-incorrect-carbonate-structure-q1b

Explain why this structure is not accepted as another resonance structure for the carbonate ion.

4c2 marks

Deduce the number of sigma (σ) and pi (π) bonds present in any of the resonance structures of the carbonate ions shown in part a).

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5a6 marks

Silicon can form silicon tetrachloride SiCl4 and also silicon hexachloride, SiCl62-.

i)
Draw the Lewis structure for SiCl4 and SiCl62-.
[2]
ii)
Use VSEPR theory to deduce the Cl-Si-Cl bond angles in both the SiCl4 and SiCl62- molecules.
[2]
iii)
Predict the molecular geometry of each molecule.
[2]
5b3 marks

Carbon can form CCl4 but cannot form CCl62-. Explain why.

5c2 marks

Deduce which, if any, of SiCl4 and SiCl62-, are polar molecules and explain your choice.

5d6 marks

Formal charge can be used to decide on the most stable, and therefore most likely, form a molecule can take. Resonance structures occur when more than one Lewis diagram describes a structure equally well.

i)
Deduce the formal charge on the silicon and each chlorine within SiCl4 and SiCl62-

[2]

ii)
Predict which will be the most stable molecule and explain your answer.

[2]

iii)
Predict if any resonance structures are possible for SiCl62- and explain your answer.

[2]

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6a4 marks

Natural rubber, polyisoprene, forms a flexible polymer in the following reaction:

 ib-hl-sq-14-1-h-structures-of-isopropene-and-polyisopropene-q3a

i)
Deduce the number of sigma (σ) and pi (π) bonds in the monomer.

[2]

ii)
Deduce the number of sigma (σ) and pi (π) bonds in the repeating unit.

[2]

6b2 marks

Deduce the number of carbons with a tetrahedral geometry in both the monomer, isoprene, and the repeating unit of the polymer, polyisoprene.

6c4 marks

Polymer formation involves a radical intermediate to lengthen the polymer chain.

The radical in the formation of polyisoprene is shown below, where X represents the existing chain:

 

X-CH2CCH3CHCH2

i)
Identify the atom that is the radical in the structure shown.
[1]
ii)
Deduce the formal charge on the radical atom.
[1]
iii)
Use the information above, and your knowledge of structure and bonding, to predict if the structure is stable or not.
[2]

6d2 marks

Isoprene is not produced directly by the rubber tree, but is the product of a series of biochemical reactions from the isopentenyl pyrophosphate molecules present in the tree.

 

The structure of isopentenyl pyrophosphate is shown below:

ib-hl-sq-14-1-h-structure-of-isopentenyl-pyrophosphate-q3d

Deduce the number of sigma (σ) and pi(π) bonds present in one molecule of isopentenyl pyrophosphate.

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7a4 marks

One interhalogen compound is IF5.

 
i)
Draw the Lewis structure for IF5.

[1]

ii)
Use VSEPR theory to deduce the bond angles in IF5.

[1]

iii)
Predict whether IF5 will be a polar molecule and explain your choice.

[2]

7b4 marks

Iodine can also form the triiodide ion, I3-.

 
i)
Draw the Lewis structure for I3-.
[1]
ii)
Use VSEPR theory to deduce the bond angles in I3-.
[1]
iii)
Explain the position of the lone pairs on the central iodine.
[2]
7c2 marks

Deduce the formal charge on each of the iodine atoms in the triiodide molecule, I3-.

7d3 marks

An alternative Lewis structure for the triiodide ion, I3-, is suggested:

ib-hl-sq-14-1-h-alternative-lewis-structure-for-the-triiodide-ion-q4d

Deduce the formal charges and use them to suggest if the structure is stable and likely to occur.

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8a3 marks

Explain why methanol is soluble in water.

8b4 marks

Methanol, ethanol and propan-1-ol are all primary alcohols. Describe and explain the trend in their melting points shown below.

 
Alcohol

Methanol

CH3OH

Ethanol

C2H5OH

Propan-1-ol

C3H7OH

Melting point / oC -97 -114 -126

8c4 marks

These longer primary alcohols have the following melting points:

 

Alcohol C4H9OH C5H11OH C6H13OH C7H15OH C8H17OH C9H19OH C10H21OH
Melting point / oC -90 -79 -52 -34 -16 -6 6

Describe and explain this trend.

8d2 marks

Predict, with a reason, whether ethanol or ethane-1,2-diol will have the higher melting point?

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9a6 marks

C2H6, C4H10 and C3H8 are alkanes.

i)
Put them in order of increasing boiling point and explain your answer.
[3]
ii)
Put them in order of increasing volatility and explain your answer.

[3]

9b5 marks
Predict, with a reason, whether the alkanes are soluble in water and propanone.

9c5 marks

Pentane can exist as isomers, including pentane, CH3CH2CH2CH2CH3 and 2,2-dimethylpropane, CH3C(CH3)2CH3.

i)
Draw skeletal formula for each isomer shown above.
[2]
ii)
Predict and explain which isomer of pentane would have the greater volatility.

[3]

9d5 marks

There are two isomers possible with the molecular formula C2H6O.

i)
Draw the skeletal formulae of both isomers

[2]

ii)
Identify the strongest type of intermolecular force present in each isomer

[2]

iii)
Predict which isomer would have the higher melting point

[1]

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10a1 mark

Ibuprofen is a common non-steroidal anti-inflammatory drug (NSAID). It contains a benzene ring and a carboxylic acid at the end of one of the branches.

ibuprofen-structure-ib-hl-sq-h-14-2-q1a

Deduce the number of resonance structures possible in the deprotonated form of ibuprofen.

10b2 marks

Deduce the number of:

i)
Sigma (σ) bonds in ibuprofen

[1]

ii)
Pi (π) electrons in ibuprofen

[1]

10c2 marks

The ibuprofen molecule contains both sp3 and sp2 hybridised orbitals.

i)
Identify how many sp3 hybrid orbitals are present.

[1]

ii)
Identify how many sp2 hybrid orbitals are present.

[1]

10d3 marks

Explain why the benzene ring is a regular, planar hexagon.

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11a2 marks

2-hydroxypropanenitrile, CH3CHOHCN, is a hydroxynitrile that can be formed from ethanal in a nucleophilic addition reaction.

Deduce the number of sigma (σ) and pi (π) bonds in a molecule of 2-hydroxypropanenitrile.

11b3 marks

Deduce the number of sp3, sp2 and sp hybrid orbitals in a molecule of 2-hydroxypropanenitrile.

11c5 marks

Describe how the concept of hybridisation can be used to explain the formation of the triple bond and C-C-N bond angle in 2-hydroxypropanenitrile.

11d3 marks

Explain why, despite the high electron density in the triple bond, the triple bonded nitrile group is a more stable structure than the following alternative Lewis structure:

alternative-lewis-structure-for-2-hydroxypropanenitrile-ib-hl-sq-h-14-2-q2d

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12a2 marks

A simple amide is HCONH2.

Draw the Lewis (electron dot) structure for this molecule.

12b6 marks

Predict and explain the bond angle around the C and N atoms.

12c4 marks

Predict the molecular geometry and the electron domain geometry around the C and N in HCONH2.

12d3 marks

State, with a reason, whether HCONH2 is a polar molecule.

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13a2 marks

Tetrafluoroethene, C2F4, and tetrafluorohydrazine, N2F4, are fluorides of adjacent elements in the Periodic Table.

Draw the Lewis (electron dot) structures for C2F4 and N2F4 showing all valance electrons.

13b5 marks

Predict and explain the F-C-F bond angle in tetrafluoroethene and the F-N-F bond angle in tetrafluorohydrazine.

13c4 marks

Tetrafluorohydrazine is a polar molecule but tetrafluoroethene is not.

Explain the difference in molecular polarity.

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14a3 marks

Draw the Lewis (electron dot) structure of the carbonate ion, CO32-.

14b3 marks

Deduce the number of possible resonance structures for the carbonate ion, CO32-, and draw two of them.

14c3 marks

Discuss how the bonding in the carbonate ion, CO32-, evidences the presence of the resonance structures.

14d2 marks

Organic molecules can also show resonance. The methanoate ion, HCOO-, shows similar resonance forms to the carbonate ion, CO32-.

The corresponding organic acid, methanoic acid, also has resonance structures.

4-2-ib-sl-sq-hard-q3d-methanoic-acid-structure

Draw another resonance structure of methanoic acid.

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15a2 marks

Some of the physical and structural properties of diamond and graphite are shown below:

 
Property Diamond Graphite
Melting Point at 1 atmosphere / K 4200 4300
Density / g cm-3 3.51 2.26
Average bond length / nm 0.155 0.142
Delocalisation No Yes
Hybridisation sp3 sp2
Electron mobility / cm2 V-1 s-1 1000 - 2000 15000 - 200000

Suggest why the melting point of graphite is higher than that of diamond, using the information in the table.

15b2 marks

Graphene has the structure of a single layer of graphite. 

Suggest, giving a reason, the electron mobility of graphene compared to graphite.

15c6 marks

Graphite is a layered giant structure, containing London dispersion forces between the layers, whereas diamond has covalent bonds across all planes.

Describe and explain, based on structure and bonding, the differences expected when each of graphite and diamond are moved across a paper surface.

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