Chemistry > Chemical Bonding and Molecular Structure > 9.0 Valence Shell Electron Pair Repulsion (VSEPR) Theory
Chemical Bonding and Molecular Structure
1.0 Ionic Bond or Electrovalent Bond
2.0 Lattice Energy
3.0 Characteristics of Electrovalent Compounds
4.0 Covalent Bond (By Mutual Sharing of Electrons)
5.0 Characteristics of Covalent Compounds
6.0 Fajan’s Rule
7.0 Hydrogen Bonding
8.0 Coordinate Bond
9.0 Valence Shell Electron Pair Repulsion (VSEPR) Theory
10.0 Valence Bond Theory
11.0 Sigma and Pi Bonds ($\sigma $ and $\pi $ Bonds)
12.0 Hybridisation
12.1 Types of hybridization and spatial orientation of hybrid orbitals
12.2 Method of predicting the Hybrid state of the central atom in covalent molecules of polyatomic ions
13.0 Molecular Orbital Theory
9.2 Effect of Electronegativity
12.2 Method of predicting the Hybrid state of the central atom in covalent molecules of polyatomic ions
$NF_3$ and $NH_3$ both have structures based on a tetrahedron with one corner occupied by a lone pair. The high electronegativity of $F$ push the bonding electrons further away from $N$ than in $NH_3$.
Hence the lone pair in $NF_3$ causes a greater distortion from tetrahedral and gives a $F – N – F$ bond angle of ${102^ \circ }30'$, compared with ${107^ \circ }48'$ in $NH_3$.
The same effect is found in $H_2O$ (bond angle ${104^ \circ }27'$) and $F_2O$ (bond angle $102^°$).
The effects of bonding and lone pairs on bond angles
Orbitals on central atom | Shape | Number of bond pairs | Number of lone pairs | Bond angle | |
$BeCl_2$ | 2 | Linear | 2 | 0 | $180^°$ |
$BF_3$ | 3 | Plane triangle | 3 | 0 | $120^°$ |
$CH_4$ $NH_3$ $NF_3$ $H_2O$ $F_2O$ | 4 4 4 4 4 | Tetrahedral Pyramidal Pyramidal Bent (V-shape) Bent (V-shape) | 4 3 3 2 2 | 0 1 1 2 2 | $109^°28'$ $107^°48'$ $102^°30'$ $104^°27'$ $102^°$ |
$PCl_5$ $SF_4$ $ClF_3$ $XeF_2$ | 5 5 5 5 | Trigonal bipyramid Trigonal bipyramid T-shape Linear | 5 4 3 2 | 0 1 2 3 | $120^°$ and $90^°$ $101^°36'$ and $86^°33'$ $87^°40'$ $180^°$ |
$SF_6$ $BrF_5$ $XeF_4$ | 6 6 6 | Octahedral Square pyramidal Square planar | 6 5 4 | 0 1 2 | $90^°$ $84^°30'$ $90^°$ |
