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
KU1 2. Define a covalent bond.
The sharing of a pair of electrons between two non-metallic atoms. 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 :
[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 / \ F F V-Shaped
 [A2] 1
4. 80% of air is nitrogen. (a) Draw the structural formula of the nitrogen molecule.
(b) State whether the nitrogen molecule is polar or non-polar.
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 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.
There is an even distribution of charge over the whole molecule. This leads to no distinct positive or negative charges being present. 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 A2
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.
(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.
(ii) Explain why a carbon–oxygen bond is polar.
There is an unequal sharing of electrons between two different nonmetallic atoms having different electronegativities. 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
(b) Draw a diagram to show the bonding and shape of a molecule of COCl2.
O Cl C Cl
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.
A2 (b) State the number of valence electrons used by the sulfur atom to form SO3.
A2 (c) State the number of electrons in the valence shell of the sulfur atom in sulfur trioxide.
(d) Name the shape of the sulfur trioxide molecule.
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.
(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. KU1 10. Nitrogen trifluoride, NF3, is a potent greenhouse gas. The amount of...
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