Question

(9) For each pair of molecules or ions below (i) Draw the Lewis dot structures. (If there is resonance, draw it.) (ii) Draw/Describe the VSEPR structures, including bonded electron pairs and lone pairs. (iii) Describe the structure of the molecule, considering all the bonds and atoms (but not lone pairs.) i.e., is the molecule straight? bent? etc. Angles between atoms? (iv) Indicate whether each molecule has a dipole moment, and mark the positive and negative poles. (v) Choose which molecule in each pair will align in an in an electric field. (Note: The first atom is the center atom of the molecule.) (a) XeF2 or IBr5 (b) CIF5 or PF5 (c) SO2 or SO3 (d) NH3 or NH4+

Answer 1

• XeF₂ :

  Central Atom - Xe ( 5s2 5p6)

  bonded atom : F ( 2s2 2p5)

  Total Valence electrons : 1*8 + 2*7 = 22

  Xe* (influence of F , excitation ) : 5s²5px²5py²5pz¹ 5d¹ (5 -sp3d hybridized orbitals )

  as per VSEPR :

  Electron geometry for sp3d : Trigonal bipyramidal

  3 lone pair on Xe .

  Molecular Geometry : Linear; Bond Angle : 180 ; Non-polar (dipole moment = 0).

• IBr₅ :

  Central Atom - I ( 5s2 5p5)

  bonded atom : Br ( 4s2 4p5)

  Total Valence electrons : 1*7 + 5*7 = 42

  I* (influence of Br , excitation ) : (6 - sp3d² hybridized orbitals )

  as per VSEPR :

  Electron geometry for sp3d² : Octahedral

  1 lone pair on I .

  Molecular Geometry : square pyramidal ; Bond Angle : 90 ; Polar (dipole moment > 0).

ClF5 :

Central Atom - Cl ( 3s2 3p5)

bonded atom : F( 2s2 2p5)

Total Valence electrons : 1*7 + 5*7 = 42

Cl* (influence of F , excitation ) : (6 - sp3d² hybridized orbitals )

as per VSEPR :

Electron geometry for sp3d² : Octahedral

1 lone pair on Cl .

Molecular Geometry : square pyramidal ; Bond Angle : 90 ; Polar (dipole moment > 0).

PF5 :

Central Atom - P ( 3s2 3p3)

bonded atom : F( 2s2 2p5)

Total Valence electrons : 1*5 + 5*7 = 40

P* (influence of F , excitation ) : (5 - sp3d hybridized orbitals )

as per VSEPR :

Electron geometry for sp3d : Trigonal bipyramidal

0 lone pair on P .

Molecular Geometry : Trigonal bipyramidal ; Bond Angle : 90, 120 ; Non-Polar (dipole moment = 0).

• SO2 and SO3 :

  SO2 :

Central Atom - S ( 3s2 3p4)

bonded atom : O( 2s2 2p4)

Total Valence electrons : 1*6 + 2*6 = 18

S* (influence of O , excitation ) : (3 - sp2 hybridized orbitals )

as per VSEPR :

Electron geometry for sp2 : Trigonal planar

1 lone pair on P ; 2 : S-O pi bonds.

Molecular Geometry : Bent/ Angular ; Bond Angle : < 120 ; Polar (dipole moment > 0).

SO3 :

Central Atom - S ( 3s2 3p4)

bonded atom : O( 2s2 2p4)

Total Valence electrons : 1*6 + 3*6 = 24

S* (influence of O , excitation ) : (3 - sp2 hybridized orbitals )

as per VSEPR :

Electron geometry for sp2 : Trigonal planar

0 lone pair on P ; 3 : S-O pi bonds.

Molecular Geometry : Trigonal planar ; Bond Angle : 120 ;Non- Polar (dipole moment = 0).

• NH3 and NH₄+ :

  NH3 :

Central Atom - N ( 2s2 2p3)

bonded atom : H( 1s1)

Total Valence electrons : 1*5 + 3*1 = 8

N* (influence of H , excitation ) : (4 - sp3 hybridized orbitals )

as per VSEPR :

Electron geometry for sp3 : Tetrahedral

1 lone pair on N

Molecular Geometry :Trigonal pyramidal ; Bond Angle : < 109.5 ; Polar (dipole moment > 0).

• NH₄+ :

Central Atom - N ( 2s2 2p3)

bonded atom : H( 1s1)

Total Valence electrons : 1*5 + 3*1 = 8

N* (influence of H , excitation ) : (4 - sp3 hybridized orbitals )

as per VSEPR :

Electron geometry for sp3 : Tetrahedral

0 lone pair on N , N- donates electron pair to H+.

Molecular Geometry :Tetrahedral ; Bond Angle : 109.5 ;Non- Polar (dipole moment = 0).