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AQA AS chem, bonding question

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    Doc3.docxQ2.Which one of the following is the most likely value for the bond angle α shown in the diagram of SF4 below?

    A 118°
    B 101°
    C 90°
    D 88°

    The anwser is A but i dont know why

    (Sulfur bonded to 4 fluorine atoms, with a lone pair)

    Imagine that lone pair were another atom and think what shape molecule that would give, and the bond angles of such a shape - then remember than the influence of a lone electron pair causes bond angles to be slightly reduced against the shape with the same amount of electron domains but all bonded.

    In this case it's got 5 electron domains - if all were bonded it would be trigonal bipyrimidal, with bond angles of 90° (axial to equatorial), 120° (eq to eq) and 180° (ax to ax). The angle α is between the two equatorial fluorine atoms, so would be 120°, but the lone pair causes that to be slightly reduced - so 118° would be a reasonable estimate for that bond angle.
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