Structure 1. Models of the particulate nature of matter

1.1 Introduction to the particulate nature of matter

1.2 The nuclear atom

1.3 Electron configurations

1.4 The mole

1.5 Ideal gases

Structure 2. Models of bonding and structure

2.1 The ionic model

2.2 The covalent model

2.3 The metallic model

2.4 From models to materials

Structure 3. Classification of matter

3.1 The periodic table

3.2 Functional groups: Organic compounds

Reactivity 1. What drives chemical reactions?

1.1 Measuring enthalpy changes

1.2 Energy cycles

1.3 Energy from fuels

Reactivity 2. How much, how fast and how far?

2.1 Amount of chemical change

2.2 Rate of chemical change

2.3 Extent of chemical change

Reactivity 3. What are the mechanisms of chemical change?

3.1 Proton transfer reactions

3.2 Electron transfer reactions

3.3 Electron sharing reactions (Radicals)

3.4 Electron-pair sharing reactions

IB Chemistry SL 2.2 The covalent model Question Bank

[Maximum number: 2]

Ethane-1,2-diol, $\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}$ , has a wide variety of uses including the removal of ice from aircraft and heat transfer in a solar cell.

(a)

Explain why the boiling point of ethane-1,2-diol is significantly greater than that of ethene.

[ 2 ]

[Maximum number: 2]

Alkanes are commonly occurring organic compounds.

(a)

The first four straight chain alkanes are gases at room temperature.

Boiling points of straight chain alkanes

[ 2 ]

(i)

Explain why the boiling point increases from methane to propane.

[ 2 ]

[Maximum number: 1]

Chlorine undergoes many reactions.

(a)

(i)

Predict, giving a reason, whether ethane or chloroethane is more reactive.

[ 1 ]

[Maximum number: 2]

Ethanedioic acid is a diprotic acid. A student determined the value of x in the formula of hydrated ethanedioic acid, $\mathrm{HOOC}-\mathrm{COOH} \bullet \times \mathrm{H}_{2} \mathrm{O}$ , by titrating a known mass of the acid with a $0.100 \mathrm{~mol} \mathrm{dm}^{-3}$ solution of NaOH(aq).
0.795 g of ethanedioic acid was dissolved in distilled water and made up to a total volume of $250 \mathrm{~cm}^{3}$ in a volumetric flask.
$25 \mathrm{~cm}^{3}$ of this ethanedioic acid solution was pipetted into a flask and titrated against aqueous sodium hydroxide using phenolphthalein as an indicator.

The titration was then repeated twice to obtain the results below.

(a)

Identify the strongest intermolecular force in solid ethanedioic acid.

[ 1 ]

(b)

Deduce the Lewis (electron dot) structure of ethanedioic acid, HOOC-COOH.

[ 1 ]

[Maximum number: 2]

The absorption of infrared (IR) radiation by molecules in the atmosphere affects global temperatures.

Graph of IR absorbances for oxygen and ozone molecules

(a)

The following data has been compiled for a range of molecules that may be found in the atmosphere.

*Integrated IR intensity is a measure of the extent to which the molecule absorbs infrared radiation passing through the atmosphere.
**GWP: The global warming potential (GWP) is a relative measure of the total contribution of the compound to global warming over the specified time period. It is compared to the same mass of $\mathrm{CO}_{2}$ , which has a GWP of 1 .

[ 2 ]

(i)

Explain the increase in molecular dipole moment as one chlorine atom in $\mathrm{CCl}_{4}$ is replaced with fluorine to produce $\mathrm{CCl}_{3} \mathrm{~F}$ .

[ 2 ]

[Maximum number: 2]

Two groups of students (Group A and Group B) carried out a project* on the chemistry of some group 7 elements (the halogens) and their compounds.

(a)

Although the molar masses of ICl and $\mathrm{Br}_{2}$ are very similar, the boiling point of ICl is $97.4^{\circ} \mathrm{C}$ and that of $\mathrm{Br}_{2}$ is $58.8^{\circ} \mathrm{C}$ . Explain the difference in these boiling points in terms of the intermolecular forces present in each liquid.

[ 2 ]

[Maximum number: 1]

In order to determine the oil content of different types of potato crisps (chips), a student weighed 5.00 g of crushed crisps and mixed them with $20.0 \mathrm{~cm}^{3}$ of non-polar solvent.

She assumed all the oil in the crisps dissolved in the solvent.
The student then filtered the mixture to remove any solids, and gently heated the solution on a hot plate to evaporate the solvent.

She measured the mass of the oil that remained from each type of crisps.

(a)

Suggest why a non-polar solvent was needed.

[ 1 ]

[Maximum number: 8]

Phosphine (IUPAC name phosphane) is a hydride of phosphorus, with the formula $\mathrm{PH}_{3}$ .

(a)

(i)

Draw a Lewis (electron dot) structure of phosphine.

[ 1 ]

(ii)

Outline whether you expect the bonds in phosphine to be polar or non-polar, giving a brief reason.

[ 1 ]

(iii)

Explain why the phosphine molecule is not planar.

[ 2 ]

(iv)

Phosphine has a much greater molar mass than ammonia. Explain why phosphine has a significantly lower boiling point than ammonia.

[ 2 ]

(b)

Phosphine is usually prepared by heating white phosphorus, one of the allotropes of phosphorus, with concentrated aqueous sodium hydroxide. The equation for the reaction is:

\mathrm{P}_{4}(\mathrm{~s})+3 \mathrm{OH}^{-}(\mathrm{aq})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow \mathrm{PH}_{3}(\mathrm{~g})+3 \mathrm{H}_{2} \mathrm{PO}_{2}^{-}(\mathrm{aq})

[ 2 ]

(i)

Identify one other element that has allotropes and list two of its allotropes.

Element:

Allotrope 1:

Allotrope 2:

[ 2 ]

[Maximum number: 7]

Phosphorus is an element that is an essential part of the biological molecules involved in both respiration and photosynthesis.

(a)

7.75 g of phosphorus was combusted in a limited supply of oxygen, the mass of the oxide produced was 13.75 g .

[ 4 ]

(i)

This oxide of phosphorus has a melting point of 296.9 K .

Outline, with reference to structure and bonding, the reasons why the melting point of this oxide is low.

[ 2 ]

(ii)

Describe the nature of the bond between oxygen and phosphorus. Use sections 9 and 17 of the data booklet.

[ 2 ]

(b)

Another compound of phosphorus is phosphine, $\mathrm{PH}_{3}$ , it forms a phosphonium ion, $\mathrm{PH}_{4}^{+}$ .

State the types of bonds present in the phosphonium ion, $\mathrm{PH}_{4}{ }^{+}$ , and explain how these bonds are formed.

[ 2 ]

(c)

Phosphorus trichloride, $\mathrm{PCl}_{3}$ , is a common compound of phosphorus.

Deduce the Lewis formula of $\mathrm{PCl}_{3}$ .

[ 1 ]

[Maximum number: 4]

The equations show steps in the formation and decomposition of ozone in the stratosphere, some of which absorb ultraviolet light.

Step $1 \quad \mathrm{O}_{2} \rightarrow 2 \mathrm{O} \cdot$

Step $2 \quad \mathrm{O} \bullet+\mathrm{O}_{2} \rightarrow \mathrm{O}_{3}$

Step $3 \quad \mathrm{O}_{3} \rightarrow \mathrm{O} \bullet+\mathrm{O}_{2}$

Step $4\quad{O} \bullet+\mathrm{O}_{3} \rightarrow 2 \mathrm{O}_{2}$

(a)

Draw the Lewis structures of oxygen, $\mathrm{O}_{2}$ , and ozone, $\mathrm{O}_{3}$ .

[ 2 ]

(b)

Discuss how the different bond strengths between the oxygen atoms in $\mathrm{O}_{2}$ and $\mathrm{O}_{3}$ in the ozone layer affect radiation reaching the Earth's surface.

[ 2 ]

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