3 (a) Fluorine is much more electronegative than both silicon and sulfur, but whereas the molecule of SF₄ has an overall dipole, that of SiF₄ has none - CIE - A-Level Chemistry - Question 3 - 2010 - Paper 1
Question 3
3 (a) Fluorine is much more electronegative than both silicon and sulfur, but whereas the molecule of SF₄ has an overall dipole, that of SiF₄ has none.
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Worked Solution & Example Answer:3 (a) Fluorine is much more electronegative than both silicon and sulfur, but whereas the molecule of SF₄ has an overall dipole, that of SiF₄ has none - CIE - A-Level Chemistry - Question 3 - 2010 - Paper 1
Step 1
Suggest a reason for this difference.
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Answer
The reason for the difference in dipoles between SiF₄ and SF₄ lies in the molecular geometry and the presence of lone pairs. SiF₄ has a tetrahedral shape with symmetrical bond angles around the silicon atom, resulting in the dipoles of the Si-F bonds cancelling each other out. In contrast, SF₄ is see-saw shaped due to the presence of a lone pair on the sulfur atom, leading to an uneven distribution of charge, and thus an overall dipole.
Step 2
Predict whether or not the following molecules will have an overall dipole.
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Answer
BCI₃: has an overall dipole (✓)
PCl₃: has an overall dipole (✓)
CCl₄: does not have an overall dipole (✓)
SF₆: does not have an overall dipole (✓)
Step 3
Suggest a reason for this difference in reactivity.
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Answer
Silicon and boron have available low-lying orbitals for bonding, which allows BCl₃ and SiCl₄ to react with water, while CCl₄ does not react as it lacks such capabilities and is more stable due to its fully filled outer shell.
Step 4
Construct equations showing the reaction of these two chlorides with an excess of water.
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