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3. Chemical bonding
A section of Chemistry, 9701
Listing 10 of 239 questions
Elements and compounds which have small molecules usually exist as gases or liquids. Chlorine, Cl 2, is a gas at room temperature whereas bromine, Br 2, is a liquid under the same conditions. Explain these observations. The gases nitrogen, N2, and carbon monoxide, CO, are isoelectronic, that is they have the same number of electrons in their molecules. Suggest why N2 has a lower boiling point than CO. A ‘dot-and-cross’ diagram of a CO molecule is shown below. Only electrons from outer shells are represented. C O In the table below, there are three copies of this structure. On the structures, draw a circle round a pair of electrons that is associated with each of the following. a co-ordinate bond a covalent bond a lone pair C O C O C O Hydrogen cyanide, HCN, is a gas which is also isoelectronic with N2 and with CO. Each molecule contains a strong triple bond with the following bond energies. bond bond energy / kJ mol–1 –CN in HCN NN CO Although each compound contains the same number of electrons and a strong triple bond in its molecule, CO and HCN are both very reactive whereas N2 is not. Suggest a reason for this. HCN reacts with ethanal, CH3CHO. Give the displayed formula of the organic product formed. What type of reaction is this? Draw the mechanism of this reaction. You should show all full and partial charges and represent the movement of electron pairs by curly arrows.
9701_s10_qp_21
THEORY
2010
Paper 2, Variant 1
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Questions Discovered
239