Chemical Bonding and Molecular Structure · Question 29

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A molecule with the formula AX4Y has all its elements from p-block. Element A is rarest, monoatomic, non-radioactive from its group and has the lowest ionization enthalpy value among A, X and Y. Elements X and Y have first and second highest electronegativity values respectively among all the known elements. The shape of the molecule is:

Pentagonal planar
Square pyramidal
Trigonal bipyramidal
Octahedral

Answer

(2) Square pyramidal

Solution

A: monoatomic, rarest non-radioactive element of its group (group 18) with the lowest ionisation enthalpy A = Xe

X = F (highest electronegativity), Y = O (second highest)

Molecule = XeOF4

Valence electrons of Xe = 8; 4 bond pairs to F, Xe=O counts as one σ bond pair (π bond not counted)

5 bond pairs + 1 lone pair = 6 electron pairs sp3d2, octahedral arrangement

With one lone pair, the shape is square pyramidal.

Answer: (2)

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Keep practising — Chemical Bonding and Molecular Structure

Among SO2, NF3, NH3, XeF2, ClF3 and SF4, the hybridization of the molecule with nonzero dipole moment and highest number of lone-pairs of electrons on the central atom is

sp3
dsp2
sp3d2
sp3d

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Which among the following molecules is (a) involved in sp3d hybridization, (b) has different bond lengths and (c) has lone pair of electrons on the central atom?

XeF4
XeF2
PF5
SF4

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An element 'E' has the ionisation enthalpy value of 374 kJ mol-1. 'E' reacts with elements A, B, C and D with electron gain enthalpy values of −328, −349, −325 and −295 kJ mol-1, respectively. The correct order of the products EA, EB, EC and ED in terms of ionic character is :