Group 7: the halogens

This question is about trends in the periodic table.

The graph shows the melting points for Period 3 elements from sodium to silicon.

Complete the graph to show approximate melting points for P, S, C l and Ar.

Explain why silicon has a higher melting point than aluminium.

Use ideas about structure and bonding in your answer.

The table shows the first ionisation energies for the elements in Period 3.

Write an equation to represent the first ionisation energy of sulfur. Include state symbols.

The table shows that there is a general increase in first ionisation energies across Period 3, but that this trend is not followed by phosphorus to sulfur.

Explain why the first ionisation energy of sulfur is lower than the first ionisation energy of phosphorus.

A student adds an aqueous solution of bromine, Br₂(aq), to two test tubes.

The student adds aqueous sodium iodide, NaI(aq), to the Br₂(aq) in one test tube, and aqueous sodium chloride, NaCl (aq), to the Br₂(aq) in the other test tube.

Complete the table to show the student's observations.

Write ionic equation(s) for any reaction(s) that take place.

Ionic equation(s)........

* The hydrides of silicon, phosphorus and sulfur have simple molecular structures, but their molecules have different shapes.

Explain why molecules of SiH₄, PH₃ and H₂S have different shapes.

Your answer should include ‘dot-and-cross’ diagrams (outer shells only), the names of the shapes and an explanation of why the bond angles are different.

Which statement explains the trend in boiling points down the halogens group?

A The bond enthalpy of the covalent bonds increases.

B The halogens become less electronegative.

C The induced dipole–dipole interactions (London forces) become stronger.

D The reactivity of the halogens decreases.

Your answer

Which equation does not represent a disproportionation reaction?

Your answer

Chlorine has the electron configuration [Ne]3s²3p⁵.

Which statement(s) about chlorine is/are correct when it reacts in redox reactions?

1 It can gain one electron to form 1– ions.

2 It can lose its 3s² electrons to form 2+ ions.

3 It can lose its 3p⁵ electrons to form 5+ ions.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

This question is about elements in the periodic table.

Chlorine has many uses.

Chlorine is used to treat water in large-scale water treatment plants.

Suggest why chlorine is added to water in large-scale water treatment plants.

Sea water contains aqueous bromide ions.

Chlorine is used to extract bromine from sea water.

Construct the ionic equation for this reaction and explain why chlorine is suitable for this extraction of bromine but iodine is not.

Equation........

Explanation........

Fluorine, F₂, reacts with nitrogen dioxide, NO₂, to form nitryl fluoride, NO₂F, as shown in Reaction 20.1 below.

The mechanism for this reaction involves two steps. Step 1 is the ‘slow’ step and Step 2 is the ‘fast’ step.

The equation for Step 2 is shown below:

Suggest the equation for Step 1 and the rate equation for Reaction 20.1.

Equation for Step 1:........

Rate equation for Reaction 20.1:........

* The table shows the melting points of some of the elements in Period 3 of the periodic table.

Element	Al	Si	P4	S8
Melting point / C	660	1410	44	119

Explain the melting points in terms of bonding and structure.

The three elements that, when in a molecule, can form hydrogen bonds with other suitable molecules.

An element that is a solid at RTP with a simple molecular lattice structure.

The two elements with atoms containing five unpaired electrons.

The element in Period 3 that exists in the solid state as a network of atoms bonded by strong covalent bonds.

The p-block element in Period 3 that forms a compound with fluorine with octahedral molecules.

The element that forms 1– ions most readily.

The element with an average atomic mass of 1.244 10^–22 g.

This question is about redox reactions.

‘Calcium hypochlorite’, Ca(Cl O)₂, is an ionic compound used in ‘bleaching powder’.

The Cl O^– ion in Ca(Cl O)₂ is the active ingredient that kills bacteria.

Calcium hypochlorite is prepared by reacting chlorine gas with calcium hydroxide.

A student analyses the redox reactions shown below. State symbols have been omitted.

The student concludes that different ions containing chromium can act as oxidising or reducing agents.

Using the terms oxidising agent and reducing agent, and ideas about electrode potentials and equilibrium, explain how the student is correct.

Include overall equations.

A student bubbles hydrogen sulfide gas, H₂S(g), through an acidified solution containing manganate(VII) ions, MnO₄^–(aq).

A redox reaction takes place, forming aqueous manganese(II) ions, a yellow precipitate and one other product.

Construct the equation for this reaction. State symbols are not required.

Which statement(s) explain(s) the trend in boiling points down the halogens group?

1: The induced dipole–dipole interactions (London forces) become stronger.

2: The covalent bonds become stronger.

3: The permanent dipole–dipole interactions become stronger.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

Which statement about the reactions of halogens with halide ions is correct?

A I₂(aq) can oxidise Br⁻(aq).

B Cl₂(aq) can reduce Br⁻(aq).

C Br⁻(aq) can reduce Cl₂(aq).

D Cl⁻(aq) can oxidise I₂(aq).

Your answer

This question is about the halogen group of elements and some of their compounds.

The halogens show trends in their properties down the group.

The boiling points of three halogens are shown below.

Explain why the halogens show this trend in boiling points.

Hydrogen iodide, H I, is decomposed by heat into its elements:

The decomposition is much faster in the presence of a platinum catalyst.

Complete the enthalpy profile diagram for this reaction using formulae for the reactants and products.

• Use E_a to label the activation energy without a catalyst.

• Use E_c to label the activation energy with a catalyst.

• Use H to label the enthalpy change of reaction.

Compound A is an oxide of chlorine that is a liquid at room temperature and pressure and has a boiling point of 83 °C.

When 0.4485 g of A is heated to 100 °C at 1.00 × 10⁵ Pa, 76.0 cm³ of gas is produced.

Determine the molecular formula of compound A.

Show all your working.

Complete Table 20.1 and calculate the mean titre that the student should use for analysing the results.

The uncertainty in each burette reading is ±0.05 cm³.

Calculate the percentage uncertainty in the titre obtained from titration 1.

Give your answer to two decimal places.

Describe and explain how the student should determine the end point of this titration accurately.

Determine the relative formula mass and formula of the Group 1 iodate(V), B.

Show your working.

Select an element from the first three periods that fits each of the following descriptions.

The element that forms a 1– ion with the same electron configuration as helium.

The element with the highest first ionisation energy.

The element in Period 3 which has the successive ionisation energies shown below.

The element which forms a compound with fluorine that has octahedral molecules.

An element which reacts with water to form an acidic solution.

The element X, which forms a compound with hydrogen, XH₃, with a molar mass of 34.0 g mol^–1.

An element which forms a compound with hydrogen in which the element has an oxidation number of –4.

The element which has a density of 1.33 × 10^–3 g cm^–3 at room temperature and pressure.

Table 1.1 shows some properties of Period 3 chlorides.

Explain the properties shown in Table 1.1 in terms of bonding and structure.