Covalent Bonding Test

Topics: Oxygen, Chemical bond, Atom Pages: 9 (1245 words) Published: June 16, 2013
Year 11 Chemist

YEAR 11 CHEMISTRY: SUMMATIVE TEST: COVALENT BONDING ANSWERS

Name: ___________________________ Total Marks 70 Marks
1. Name the theory used to predict the shapes of molecules.

Valence Shell Electron Pair Repulsion Theory
[1]KU1 2. Define a covalent bond.

The sharing of a pair of electrons between two non-metallic atoms. [2]KU1 3. (a) Draw electron dot structures (Lewis diagrams) for each of the following molecules. (i) Oxygen (O2) (ii) Fluorine monoxide (F2O)

..

..

:O: .. :F: .. .. :F: ..

:O :: O :

[4][KU1] (b) Draw structural formulae for the two molecules above clearly indicating the shape of the molecule and any required unbonded electrons. State the shape of each molecule. (i) (ii)

O

O

.. .. O / \ F F V-Shaped
[6] [A2] 1

Linear

2012CovalentBondingTest@AdelaideHighSchoolJohnPapanicolas

4. 80% of air is nitrogen. (a) Draw the structural formula of the nitrogen molecule.

N

N
[2]KU1

(b) State whether the nitrogen molecule is polar or non-polar.

Non-polar
[1]A2 5. Silicon forms a number of molecular silicon hydrides, the simplest of which has the formula SiH4. (a) State the shape of a SiH4 molecule, and explain why it has this shape. Shape:Tetrahedral [1]A2 Explanation: There are four regions of electron sharing repelled as far as

possible around the central silicon atom. Electrons and atoms are distributed in a tetrahedral arrangement. (b) State and explain whether the SiH4 molecule is polar or non-polar.

[2]KU1

There is an even distribution of charge over the whole molecule. This leads to no distinct positive or negative charges being present. [3]KU3 (c) SiH4 burns spontaneously in air due the presence of oxygen, producing silicon dioxide and water. Write an equation for this reaction. SiH4 + 2O2  SiO2 + 2H2O [2]A2

2012CovalentBondingTest@AdelaideHighSchoolJohnPapanicolas

2

6. Liquid carbon dioxide, held under very high pressure, is an alternative to conventional dry-cleaning solvents. The liquid carbon dioxide used is recycled. (a) Draw the structural formula of carbon dioxide.

O
(b)

C

O
[2]KU1

(i) Draw a diagram to show the polarity of a covalent bond between a carbon atom and an oxygen atom using the appropriate fractional charges.

δ+ δC-O

[1]KU1

(ii) Explain why a carbon–oxygen bond is polar.

There is an unequal sharing of electrons between two different nonmetallic atoms having different electronegativities. [2]A2 7. Phosgene, COCl2, is a colourless, poisonous gas used in the production of insecticides and plastics. (a) State the covalence of each element in phosgene.

Element C O Cl

Covalence 4 2 1
[3]KU1

(b) Draw a diagram to show the bonding and shape of a molecule of COCl2.

O Cl C Cl
[2]A2 2012CovalentBondingTest@AdelaideHighSchoolJohnPapanicolas 3

8. In an industrial blast furnace pure oxygen is used to prepare steel. During this process sulfur trioxide is also produced which is a major pollutants that contribute to the formation of acid rain in industrialised countries. Sulfur trioxide has the molecular shape shown below:

(a) State whether sulfur has a high, an intermediate, or a low electronegativity.

High

[1]A2 (b) State the number of valence electrons used by the sulfur atom to form SO3.

Six/6
[1]A2 (c) State the number of electrons in the valence shell of the sulfur atom in sulfur trioxide.

Twelve/12
(d) Name the shape of the sulfur trioxide molecule.

[1]KU1

Trigonal Planar
[1]A2 9. Consider the PCl5 molecule drawn below
Cl Cl Cl P Cl Cl

(a) State the number of valence electrons used by the phosphorus atom to form the PCl5 molecule.

Five/5

[1]A2

2012CovalentBondingTest@AdelaideHighSchoolJohnPapanicolas

4

(b) Phosphorous has the ability to expand its octet. Explain.

Phosphorus is in period 3 and its third shell can hold up to eighteen electrons. [2]KU1 10. Nitrogen trifluoride, NF3, is a potent greenhouse gas. The amount of...
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