ALS4SA - Section 4/ Bonding and Structure II (4.5 - 4.7...

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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. [2] (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.. [2] 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. [2] 81 IB Q.5 (c) H-bonds between (protein) fibres are replaced by H-bonds to the water molecules , therefore weakening the overall structure. [2] 81 IB Q.7 (a) The C- C bond in diamond is formed by overlapping of 2 sp 3 hybrid orbitals of carbon. [1] The C- C bond in graphite is formed by (1) overlapping of 2 sp 2 hybrid orbitals of C [1] (2) delocalization of electrons by overlapping of the p-orbitals of the C atom. [1] The C- C bond is stronger in graphite than in diamond, therefore, the C- C bond in graphite has shorter bond length. [1] (b) A pure covalent bond is formed only between two similar (identical) atoms (atoms of the same electronegativites) [1] When two atoms are different and have different electronegativities , the pair of electrons forming the bond cannot be shared equally . [1] There would be an electron displacement towards the atom of higher electronegativity. [1] 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 . [1] When an ionic bond is formed between A + and B- . Owing to the charge, the A + attracts the outer electrons of B- . [1] This causes displacement of the outer electrons of B- towards A + . [1] The effect of polarization causes the electrons to be shared . Thus the ionic bond has a certain amount of covalent character . [1] (c) (i) Cubic close packing or face-centred cubic close packing. [1] (ii) hexagonal close packing. [1] (iii) 12 [1] (iv) 4 [1] (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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ALS4SA - Section 4/ Bonding and Structure II (4.5 - 4.7...

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