**PF**_{3}, PCl_{3}, PBr_{3}and PI_{3 }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**s****ingle bonded to each halogens (X)**.**P will have a lone pair**in this case while**halogen atom has 3.**- Formula appears to be
**AX**where A is the central atom, X is the atoms and E is the lone pairs attached, this particular structure follows a_{3}E_{1}**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 PX
_{3}(X = halogen) will appear as:

The bond angles increase steadily in the series
PF_{3}, PCl_{3}, PBr_{3} and PI_{3}. After consulting the data on atomic radii in Chapter 8 in the textbook,
provide an explanation for this observation.

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