Chemistry Practice Problems Bond Angles Practice Problems Solution: The bond angles increase steadily in the series PF...

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Solution: The bond angles increase steadily in the series PF3, PCl3, PBr3 and PI3. After consulting the data on atomic radii in Chapter 8 in the textbook, provide an explanation for this observation.

Problem

The bond angles increase steadily in the series PF3, PCl3, PBr3 and PI3. After consulting the data on atomic radii in Chapter 8 in the textbook, provide an explanation for this observation.

Solution
  • PF3, PCl3, PBr3 and PIwill appear to have the same geometry since F, Cl, Br and I are in the same group (column). They will appear to have the same number of valence electrons
  • P will appear to have 5 while F, Cl, Br and I have 7 valence electrons. Total valence electrons for each molecule is 26 (5(1) + 7(3) = 26). 
  • P will be the central atom (less electronegative) while being single bonded to each halogens (X). P will have a lone pair in this case while halogen atom has 3. 
  • Formula appears to be AX3E1 where A is the central atom, X is the atoms and E is the lone pairs attached, this particular structure follows a trigonal pyramidal geometry.
  • Since it has 4 groups on it, it is expected to follow a bond angle of 109.5° (bond angles of tetrahedral structure) however it deviates due to the presence of lone pairs. Expected bond angles will appear as < 109.5° due to the lone pair repelling other groups.
  • General structure of the molecules as PX3 (X = halogen) will appear as:
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