Syllabus Edition

First teaching 2014

Last exams 2024

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Resonance, Shapes & Giant Structures (DP IB Chemistry: SL)

Exam Questions

3 hours43 questions
1a3 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]
1b4 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]
1c4 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 8 of the Data booklet.

1d2 marks

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

Explain why PCl4+ is not a polar molecule.

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2a3 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]

2b3 marks

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

Explain your answer.

2c3 marks

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

2d3 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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3a4 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.

3b3 marks

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

3c4 marks

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

3d2 marks

Graphene can be made from graphite.

Describe a similarity and difference between these two structures.

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4a4 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.

4b3 marks

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

Explain how this links to the formula of each compound.

4c2 marks

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

4d4 marks
Predict and explain the solubility of both SiO2 and CO2 in water.

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1a2 marks

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

1b3 marks

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

1c4 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.

1d2 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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2a2 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.

2b5 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.

2c4 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.            

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

2d4 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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3a3 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.

3b3 marks

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

3c3 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.

3d4 marks

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

i)        BF3 

ii)       NBr3

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4a5 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.

4b2 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.

4c4 marks

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

4d1 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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5a2 marks

Draw the resonance structures for the following ions:

i)        Methanoate, HCOO-.

ii)       Nitrate(III), NO2.

5b3 marks

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

5c3 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.

5d2 marks

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

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1a2 marks

A simple amide is HCONH2.

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

1b6 marks

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

1c4 marks

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

1d3 marks

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

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2a2 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.

2b5 marks

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

2c4 marks

Tetrafluorohydrazine is a polar molecule but tetrafluoroethene is not.

Explain the difference in molecular polarity.

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3a3 marks

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

3b3 marks

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

3c3 marks

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

3d2 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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4a2 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.

4b2 marks

Predict the bond order in both diamond and graphite.

4c2 marks

Graphene has the structure of a single layer of graphite. 

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

4d6 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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