1.3 Bonding

Section A

For each of the questions only one of the lettered responses (A - D) is correct.

Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet.

1. In which one of the following pairs have the compounds the same type of bonding and shape.

A BF₃ and NH₃

$B CH₄ and SiCl₄

C HCl and H₂O

D CO₂ and SiO₂

2. Which one of the following is the correct description of the shape of the NH₃ molecule?

A trigonal planar

B tetrahedral

C square planar

@D pyramidal

3. Which one of the following pairs of molecules has similar bond angles?

A C₂H₄ and BF₃

B H₂O and CO₂

C BeCl₂ and CH₄

D SF₆ and C₂H₆

4. In which one of the following pairs do both compounds contain tetrahedral bond angles between atoms?

A BeCl₂ and BCl₃

B CCl₄ and CH₄

C SF₆ and H₂S

D NH₃ and H₂O

Section B

1. The shapes of covalent molecules can be explained using the electron pair repulsion theory.

(a) Draw the shapes of the following molecules.

methane tetrahedral (2)

[2]

water

bent or V-shaped (2)

[2]

carbon dioxide

linear (2)

[2]

(b) Using methane, water and carbon dioxide describe the principles of the electron pair repulsion theory and how it explains their shape. (Up to 2 marks may be obtained for the quality of written communication in this part).

Covalent bonds contain electron pairs (1)/ positioned around central atom (1)/ electron pairs repel each other (1)/ repulsions decrease in order lone pair:lone pair~lone pair: bond pair~bond pair:bond pair (1)/In methane all bond pairs therefore all angles equal (1)/ In water, lone pairs repel bond pairs hence bent molecule (1)/ In CO₂ pairs as far apart as possible (1) ANY SIX FROM SEVEN Quality of written communication (2)

[8]

(c) Using the electron pair repulsion theory draw a possible shape for PF₃.

Explain your reasoning.

Trigonal pyramidal

Phosphorus, when bonded, has a full octet of electrons arranged tetrahedrally (1)/ three pairs bond to fluorine (1)/ the fourth is a lone pair (1)/ repulsion between lone pair:bond pair greater than that between bond pair:bond pair (1) [5]

2. Beryllium occurs to a small extent in the earth's crust. It is a steel-grey metal, which is extremely light.

Draw and explain the shape of beryllium chloride using the electron pair repulsion theory.

Shape

Explanation

[5]

3. Sulphur burns in fluorine to form sulphur hexafluoride. Draw the shape of the molecule and explain it in terms of electron pair repulsion theory.

[3]