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Unformatted text preview: Section 4/ Bonding and Structure II (4.5 - 4.7 Metallic bonding and The relationship between structures and properties of materials) / Suggested solutions / SKH Bishop Baker Secondary School A-Level Chemistry Section 4 Bonding and Structure II (4.5 - 4.7 Metallic bonding and The relationship between structures and properties of materials) 80 IIB Q.6 (a) This is because van der Waals forces increase down the group.  (b) (i) (ii) Carbon dioxide is a simple molecular compound, only very weak van der Waals forces exist between discrete CO 2 molecules . Silicon dioxide is a giant covalent compound , strong Si- O covalent bonds exist over the entire giant structure which is similar to that of diamond. Therefore silicon dioxide has a much greater m.p..  81 IA Q.2 (a) O 2 molecules, being smaller and lighter than C 4 H 10 : have higher kinetic energies . Therefore, even under high pressure, O 2 molecules will not condense to form liquid state at room temperature. The attractive (cohesive) forces between C 4 H 10 molecules are greater than those between O 2 molecules.  81 IB Q.5 (c) H-bonds between (protein) fibres are replaced by H-bonds to the water molecules , therefore weakening the overall structure.  81 IB Q.7 (a) The C- C bond in diamond is formed by overlapping of 2 sp 3 hybrid orbitals of carbon.  The C- C bond in graphite is formed by (1) overlapping of 2 sp 2 hybrid orbitals of C  (2) delocalization of electrons by overlapping of the p-orbitals of the C atom.  The C- C bond is stronger in graphite than in diamond, therefore, the C- C bond in graphite has shorter bond length.  (b) A pure covalent bond is formed only between two similar (identical) atoms (atoms of the same electronegativites)  When two atoms are different and have different electronegativities , the pair of electrons forming the bond cannot be shared equally .  There would be an electron displacement towards the atom of higher electronegativity.  As a result of electron displacement, the more electronegative atom acquires a partial 1 Section 4/ Bonding and Structure II (4.5 - 4.7 Metallic bonding and The relationship between structures and properties of materials) / Suggested solutions / negative charge while the less electronegative atom acquires a partial positive charge. Thus the covalent bond has a certain amount of ionic character .  When an ionic bond is formed between A + and B- . Owing to the charge, the A + attracts the outer electrons of B- .  This causes displacement of the outer electrons of B- towards A + .  The effect of polarization causes the electrons to be shared . Thus the ionic bond has a certain amount of covalent character .  (c) (i) Cubic close packing or face-centred cubic close packing.  (ii) hexagonal close packing.  (iii) 12  (iv) 4  (v) Volume of 4 moles of Cu atoms = 6x 10 23 x l 3 cm 3 where l = length of side of a unit cell (in cm) Density of Cu = 8.9 g cm-3 = 4 x 63.5/6 x 10 23 x l 3 g cm...
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