(a)

Gaseous ammonia and hydrogen fluoride react together to give solid ionic ammonium fluoride.

\mathrm{NH}_{3}(\mathrm{~g})+\mathrm{HF}(\mathrm{~g}) \rightleftharpoons \mathrm{NH}_{4} \mathrm{~F}(\mathrm{~s}) \quad \Delta H=-147 \mathrm{~kJ} \mathrm{~mol}^{-1}

[ 3 ]

(i)

There are three types of bonding in $\mathrm{NH}_{4} \mathrm{~F}$ .

Give the names of each of the three types, and state where in the compound each type occurs.

[ 3 ]

(b)

Many commercial copper and brass polishes contain ammonia. The tarnish that forms on the surface of copper is often copper sulfide, CuS . In the presence of $\mathrm{O}_{2}$ from the air, $\mathrm{NH}_{3}$ can combine with this copper sulfide to produce the soluble cuprammonium sulfate, $\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{SO}_{4}$ .

[ 1 ]

(i)

Construct an equation for this reaction.

[ 1 ]

(a)

Magnesium nitrate, $\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}$ , is very soluble in water. When a hot saturated solution of magnesium nitrate is cooled, crystals of the hydrate, $\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}$ , are formed.
In the crystals, six water molecules bond to each $\mathrm{Mg}^{2+}$ ion, and some of these water molecules are also bonded to the nitrate ions.

[ 1 ]

(i)

Describe the arrangement of the water molecules around the $\mathrm{Mg}^{2+}$ ion.

[ 1 ]

[Maximum number: 2]

Sodium oxide, $\mathrm{Na}_{2} \mathrm{O}$ , is a white crystalline solid with a high melting point.

(a)

Write an equation for the reaction of sodium with oxygen, forming sodium oxide. Include state symbols.

[ 2 ]

[Maximum number: 3]

Ammonia, $\mathrm{NH}_{3}$ , and methane, $\mathrm{CH}_{4}$ , are the hydrides of elements which are next to one another in the Periodic Table.

(a)

When ammonia gas is mixed with hydrogen chloride, white, solid ammonium chloride is formed.

State each type of bond that is present in one formula unit of ammonium chloride and how many of each type are present.
You may draw diagrams.

[ 3 ]

(a)

Sodium and silicon also react directly with chlorine to produce the chlorides shown.

[ 2 ]

(i)

Describe what you would see during the reaction between sodium and chlorine.

[ 2 ]

[Maximum number: 2]

Aluminium is a metal in Period 3 and Group III of the Periodic Table.

(a)

Aluminium reacts with chlorine to form a white, solid chloride that contains 79.7 % chlorine and sublimes (changes straight from a solid to a gas) at $180^{\circ} \mathrm{C}$ .

[ 2 ]

(i)

Describe the structure and bonding in this compound. Suggest how it explains the low sublimation temperature.

[ 2 ]

(a)

One of the factors that determines the type of bonding present between the particles of a substance is the relative electronegativities of the bonded particles.

[ 2 ]

(i)

Name and describe the type of bonding you would expect to find between particles with very different electronegativities.

[ 2 ]

[Maximum number: 2]

Species such as $\mathrm{NH}_{4}{ }^{+}, \mathrm{CO}_{3}{ }^{2-}$ and $\mathrm{PO}_{4}{ }^{3-}$ are examples of molecular ions.

(a)

Ionic and covalent bonds both involve an electrostatic attraction between different species.

Identify the species that are electrostatically attracted to one another in:
- an ionic bond
- a covalent bond.

[ 2 ]

[Maximum number: 2]

Aluminium is a metal in Period 3 and Group III of the Periodic Table.

(a)

Aluminium reacts with chlorine to form a white, solid chloride that contains 79.7 % chlorine and sublimes (changes straight from a solid to a gas) at $180^{\circ} \mathrm{C}$ .

[ 2 ]

(i)

Describe the structure and bonding in this compound. Suggest how it explains the low sublimation temperature.

[ 2 ]

[Maximum number: 1]

Solid aluminium chloride sublimes at $178^{\circ} \mathrm{C}$ .

Which structure best represents the species in the vapour at this temperature?

A

B

C

D

$\mathrm{A} l^{3+}\left(\mathrm{C} l^{-}\right)_{3}$