[Maximum number: 4]

The elements sodium to chlorine, in the third period, all form oxides.

(a)

Draw a diagram to show the shape of the molecule of each of the oxides, $\mathrm{SO}_{3}$ and $\mathrm{Cl}_{2} \mathrm{O}$ .

Name each shape.
In $\mathrm{SO}_{3}$ each oxygen atom forms a double bond with the sulfur atom.
$\mathrm{SO}_{3}$

[ 4 ]

[Maximum number: 1]

What are the shapes of the molecules of water and boron trifluoride?

$\mathrm{H}_{2} \mathrm{O}$

$\mathrm{BF}_{3}$

linear

pyramidal

linear

trigonal

non-linear

pyramidal

non-linear

trigonal

[Maximum number: 2]

Oxides are compounds which usually contain oxygen combined with one other element.
Oxides are classified as follows.
acidic alkaline amphoteric basic

(a)

Another sulfur compound which is present in the Earth's atmosphere is carbonyl sulfide, OCS. The sequence of atoms in the molecule is oxygen-carbon-sulfur and the molecule is not cyclic.

[ 2 ]

(i)

Suggest a value for the O-C-S bond angle.

[ 2 ]

[Maximum number: 2]

The elements of the third period of the Periodic Table, sodium to sulfur, all form chlorides by direct combination.

(a)

Sulfur forms the compound $\mathrm{S}_{4} \mathrm{~N}_{4}$ with nitrogen. The structure of $\mathrm{S}_{4} \mathrm{~N}_{4}$ is shown below. Assume all bonds shown are single bonds.

[ 2 ]

(i)

Which bond angle, a or b, in the $\mathrm{S}_{4} \mathrm{~N}_{4}$ molecule will be smaller? Explain your answer.

[ 2 ]

[Maximum number: 7]

Valence Shell Electron Pair Repulsion theory (VSEPR) is a model of electron-pair repulsion (including lone pairs) that can be used to deduce the shapes of, and bond angles in, simple molecules.

(a)

Complete the table below by using simple hydrogen-containing compounds. One example has been included.

[ 3 ]

(b)

Tellurium, Te, proton number 52, is used in photovoltaic cells.

When fluorine gas is passed over tellurium at $150^{\circ} \mathrm{C}$ , the colourless gas $\mathrm{TeF}_{6}$ is formed.

[ 4 ]

(i)

What will be the shape of the $\mathrm{TeF}_{6}$ molecule?

[ 1 ]

(ii)

What is the F-Te-F bond angle in $\mathrm{TeF}_{6}$ ?

[ 3 ]

(a)

Sulfur reacts with fluorine to form $\mathrm{SF}_{6}$ . State the shape and bond angle of $\mathrm{SF}_{6}$ .
shape of $\mathrm{SF}_{6}$
bond angle of $\mathrm{SF}_{6}$

[ 2 ]

(a)

Phosphorus reacts with chlorine to form $\mathrm{PCl}_{5}$ .

State the shape of and two different bond angles in a molecule of $\mathrm{PCl}_{5}$ .
shape of $\mathrm{PCl}_{5}$
bond angles in $\mathrm{PCl}_{5}$

[ 2 ]

[Maximum number: 4]

The elements sodium to sulfur react with chlorine. The melting points of some of the chlorides formed are shown.

(a)

Predict the shapes of $\mathrm{AlCl}_{3}$ and $\mathrm{PCl}_{3}$ .

Draw diagrams to show the shapes, name the shapes and state the bond angles.
$\mathrm{AlCl}_{3}$
shape
angle

[ 4 ]

[Maximum number: 1]

In which species does the underlined atom have an incomplete outer shell?

A

$\mathrm{BF}_{3}$

B

$\underline{\mathrm{CH}}_{3}^{-}$

C

$\mathrm{F}_{2} \underline{\mathrm{O}}$

D

$\mathrm{H}_{3} \underline{\mathrm{O}}^{+}$

(a)

Group 2 carbonates decompose when heated to form the metal oxide and carbon dioxide.

[ 1 ]

(i)

Suggest a mechanism for the decomposition of the carbonate ion by adding two curly arrows in Fig. 1.1.

Fig. 1.1

[ 1 ]

(b)

Potassium disulfite, $\mathrm{K}_{2} \mathrm{~S}_{2} \mathrm{O}_{5}$ , is another food additive. The disulfite ion, $\mathrm{S}_{2} \mathrm{O}_{5}{ }^{2-}$ , has the displayed formula shown in Fig. 1.2.

Fig. 1.2

Deduce the geometry (shape) around the $\mathrm{S}(\alpha)$ atom in $\mathrm{S}_{2} \mathrm{O}_{5}{ }^{2-}$ .
geometry around $\mathrm{S}(\alpha)$