OCR A Jan 2011 Paper 1 Q3

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Linus Pauling was a Nobel prize winning chemist who devised a scale of electronegativity. Some Pauling electronegativity values are shown in the table. element electronegativity Br 2.0 2.8 3.0 4.0 (a) What is meant by the term electronegativity?[2] (b) Show, using + andsymbols, the permanent dipoles on each of the following bonds. NF NBr [1]OCR 2011<br />
 (c) Boron trifluoride, BF3, ammonia, NH3, and sulfur hexafluoride, SF6, are all covalent compounds. The shapes of their molecules are different. (i) State the shape of a molecule of SF6.[1] (ii) Using outer electron shells only, draw dot-and-cross diagrams for molecules of BF3 and NH3. Use your diagrams to explain why a molecule of BF3 has bond angles of 120 and NH3 has bond angles of 107. BF3 NH3[5] (iii) Molecules of BF3 contain polar bonds, but the molecules are non-polar. Suggest an explanation for this difference.[2]OCR 2011 [Total: 11] Turn over<br />

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