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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.
- PF3, PCl3, PBr3 and PI3 will 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: