Question

Use VSEPR theory to predict bond angles in the following covalently bonded molecules. Explain your predictions.

Answer 1

Answer: Bond angle for methane is 109.5°,Bond angle for ammonia is 107° and Bond angle for water is 104.5°

: $Formula used :{\text{Number of electrons}} =\frac{1}{2}[V+N-C+A]$

where, V = number of valence electrons present in central atom

N = number of monovalent atoms bonded to central atom

C = charge of cation

A = charge of anion

a. Methane:$CH_4$

In the given molecule, carbon is the central atom and there are 4 Hydrogens as monovalent atoms.

$Formula used :{\text{Number of electrons}} =\frac{1}{2}[4+4-0+0]=4$

The number of electrons is 4 that means the hybridization will be $sp^3$ and geometry of the molecule will be tetrahedral.The bond angle for terahedral geometry is 109.5°.

b. Ammonia:$NH_3$

In the given molecule, nitrogen is the central atom and there are 3 Hydrogens as monovalent atoms.

$Formula used :{\text{Number of electrons}} =\frac{1}{2}[5+3-0+0]=4$

The number of electrons is 4 that means the hybridization will be $sp^3$ and geometry of the molecule will be pyramidal as there are three bond pairs and one lone pair.The bond angle for pyramidal geometry is 107°.the bond angle reduces due to lone pair bond pair repulsions.

c. water :$H_2O$

In the given molecule, oxygen is the central atom and there are 2 Hydrogens as monovalent atoms.

$Formula used :{\text{Number of electrons}} =\frac{1}{2}[6+2-0+0]=4$

The number of electrons is 4 that means the hybridization will be $sp^3$ and geometry of the molecule will be bent as there are two bond pairs and two lone pairs.The bond angle for pyramidal geometry is 104.5°.The bond angle reduces further due to greater lone pair-lone pair repulsions.

Answer 2

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Among the choices provided above the answer should be water.

Please see below:

methane = CH4
 Shape = (4 + 4)/2 = 4 tetrahedral angle 109.5

ammonia = NH3
 shape = (5 +3)/2 = 4 but it has 1 lone pair (repulsion) angle 107.5

water H20
 (6 + 2)/2 it has 2 Lp So bond angle is 104.5