3.4. Covalent bonding and coordinate (dative covalent) bonding
A subsection of Chemistry, 9701, through 3. Chemical bonding
Listing 10 of 93 questions
The 3d orbitals in an isolated Fe2+ ion are degenerate. Complete the diagram to show the splitting of the 3d orbital energy levels in an isolated Fe2+ ion and when Fe2+ forms an octahedral complex. energy Fe2+ in an octahedral complex isolated Fe2+ ion  Bipyridine, bipy, is a bidentate ligand. N N bipy Explain what is meant by bidentate ligand. The complex 2+ exists as two stereoisomers. Complete the three-dimensional diagrams to show the two stereoisomers of 2+. State the type of stereoisomerism shown. Use N N to represent bipy in your diagrams. Fe Fe type of stereoisomerism  Standard electrode potentials can be used to compare the stability of different complex ions for a given transition element. Table 4.1 lists electrode potentials for some electrode reactions for Fe3+ / Fe2+ systems. Table 4.1 electrode reaction E o / V [Fe(H2O)6]3+ + e– [Fe(H2O)6]2+ +0.77 [Fe(CN)6]3– + e– [Fe(CN)6]4– +0.36 3+ + e– 2+ +0.96 Use relevant data from Table 4.1 to state which iron(complex is hardest to reduce. Explain your choice. iron(complex explanation  The ligand bipyridine consists of two pyridine rings. Pyridine, C5H5N, and benzene, C6H6, have similar planar, cyclic structures. N pyridine By reference to the hybridisation of the carbon atoms and the nitrogen atom, and orbital overlap, suggest how the σ and π bonds are formed in a pyridine molecule. Pyridine reacts with Cl 2 in the presence of Al Cl 3 as shown in . N pyridine N 3-chloropyridine + Cl 2 + HCl Al Cl 3 Cl The mechanism of this reaction is similar to that of the chlorination of benzene. Al Cl 3 reacts with chlorine to generate an electrophile, Cl +. Complete the diagram to show the mechanism for the reaction of pyridine with Cl +. Include all relevant charges, dipoles, lone pairs of electrons and curly arrows as appropriate. N Cl +  
9701_s22_qp_41
THEORY
2022
Paper 4, Variant 1
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The 3d orbitals in an isolated Fe2+ ion are degenerate. Complete the diagram to show the splitting of the 3d orbital energy levels in an isolated Fe2+ ion and when Fe2+ forms an octahedral complex. energy Fe2+ in an octahedral complex isolated Fe2+ ion  Bipyridine, bipy, is a bidentate ligand. N N bipy Explain what is meant by bidentate ligand. The complex 2+ exists as two stereoisomers. Complete the three-dimensional diagrams to show the two stereoisomers of 2+. State the type of stereoisomerism shown. Use N N to represent bipy in your diagrams. Fe Fe type of stereoisomerism  Standard electrode potentials can be used to compare the stability of different complex ions for a given transition element. Table 4.1 lists electrode potentials for some electrode reactions for Fe3+ / Fe2+ systems. Table 4.1 electrode reaction E o / V [Fe(H2O)6]3+ + e– [Fe(H2O)6]2+ +0.77 [Fe(CN)6]3– + e– [Fe(CN)6]4– +0.36 3+ + e– 2+ +0.96 Use relevant data from Table 4.1 to state which iron(complex is hardest to reduce. Explain your choice. iron(complex explanation  The ligand bipyridine consists of two pyridine rings. Pyridine, C5H5N, and benzene, C6H6, have similar planar, cyclic structures. N pyridine By reference to the hybridisation of the carbon atoms and the nitrogen atom, and orbital overlap, suggest how the σ and π bonds are formed in a pyridine molecule. Pyridine reacts with Cl 2 in the presence of Al Cl 3 as shown in . N pyridine N 3-chloropyridine + Cl 2 + HCl Al Cl 3 Cl The mechanism of this reaction is similar to that of the chlorination of benzene. Al Cl 3 reacts with chlorine to generate an electrophile, Cl +. Complete the diagram to show the mechanism for the reaction of pyridine with Cl +. Include all relevant charges, dipoles, lone pairs of electrons and curly arrows as appropriate. N Cl +  
9701_s22_qp_43
THEORY
2022
Paper 4, Variant 3
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This question is about the bonding of covalent compounds. On the axes below, sketch the shapes of a 1s, a 2s, and a 2px orbital. z x y 1s z x y 2s z x y 2px Covalent bonding occurs when two atoms share a pair of electrons. Covalent bonding may also be described in terms of orbital overlap with the formation of σ bonds. How are the two atoms in a covalent bond held together? In your answer, state which particles are attracted to one another and the nature of the force of attraction. Draw sketches to show orbital overlap that produces the σ bonding in the H2 and HCl molecules. H2 HCl The bond in the HCl molecule is said to be ‘polar’. What is meant by the term bond polarity? Explain why the HCl molecule is polar. Examiner’s Use The bonding in ethene may be described as a mixture of σ and π bonding. Each carbon atom in ethene forms three σ bonds as shown below. C H H H H C On the diagram, sketch the π bond that is also present in ethene. Carbon, hydrogen and ethene each burn exothermically in an excess of air. C+ O2→ CO2∆H o c = –393.7 kJ mol–1 H2+ ½O2→ H2O∆H o c = –285.9 kJ mol–1 C2H4+ 3O2→ 2CO2+ 2H2O∆H o c = –1411.0 kJ mol–1 Use the data to calculate the standard enthalpy change of formation, ∆H o f , in kJ mol–1, of ethene at 298 K. 2C+ 2H2→ C2H4∆H o f = kJ mol–1
9701_w07_qp_2
THEORY
2007
Paper 2, Variant 0
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In recent years a great deal of research has been carried out into finding different anti-cancer drugs. Tumours, which are often symptoms of cancer, are produced when cells replicate uncontrollably. This in turn is brought about by the replication of DNA in these cells. Two anti-cancer agents are mechlorethamine and cis-platin. They work by binding to the DNA and preventing replication. CH3 NH3 NH3 Pt N Cl Cl Cl Cl CH3 N G DNA DNA mechlorethamine crosslinked DNA cis-platin G NH3 NH3 Pt G G C C What type of bonding attaches both anti-cancer agents to the DNA? Suggest how each of the anti-cancer agents prevents replication of the DNA.
9701_w09_qp_41
THEORY
2009
Paper 4, Variant 1
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Questions Discovered
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