Bond Angle | Steps to Determine the Bond Angle

In a molecule, the angle between two bonds is called the bond angle. It is not important to know the bond angle, but how determining the bond angle is important. If we have two molecules NH₃ and PH₃, which one has more bond angle? To compare the bond angle between two molecules, it is important to understand the steps to find the bond angle.

What are the steps to determine the Bond Angle?

1. To check the hybridization of the central atom
2. If the hybridization of the central atom is the same, then check the lone pair on the central atom
3. If the hybridization of the central atom and the lone pair on the central atom is the same, then check the electronegativity of the central atom and surrounding atoms depending on the situation that we discussed in detail.

To Check the Hybridization of Central atom

First, check the hybridization of the central atom. The formula to calculate the hybridization of the central atom is:

Z = 1/2 (Number of valence electrons of central atom + number of negative charge – number of +ve charge + number of mono-valent atoms)

• If the hybridization is sp³, the geometry of the molecule is tetrahedral and the bond angle is 109.28°.
• If the hybridization is sp², the geometry of the molecule is trigonal and the bond angle is 120°.
• If the hybridization is sp, the geometry of the molecule is linear and the bond angle is 180°.

So the order will be

sp³ < sp² < sp

If the Hybridization of the Central Atom is the Same, then Check the Lone pair on the Central Atom

“More the lone pair on the central atom, the lesser will be the bond angle”

If the Hybridization of the Central Atom and the Lone pair on the Central Atom is the Same, then

• If the central angle is different and the surrounding atoms are the same, check the electronegativity of the central atom. The more the electronegativity of the central atom, the greater will be the bond angle.
• If the central angle is the same and the surrounding atoms are different, check the electronegativity of the surrounding atom. The more the electronegativity of the surrounding atom, the lesser will be the bond angle.

Practice Question

Which has more the bond angle BeCl₂, BCl₃, or CCl₄?

First, check the hybridization (Z) for all molecules.

Hybridization of BeCl₂

Z = 1/2 (Number of valence electrons of central atom + number of negative charge – number of +ve charge + number of mono-valent atoms)

Z = 1/2 (2 + 0 – 0 + 2)

Z = 1/2 (4)

Z = 2

sp hybridization

Hybridization of BCl₃

Z = 1/2 (3 + 0 – 0 + 3)

Z = 1/2 (6)

Z = 3

sp² hybridization

Hybridization of CCl₄

Z = 1/2 (4 + 0 – 0 + 4)

Z = 1/2 (8)

Z = 4

sp³ hybridization

As we know that the bond angle of sp, sp², and sp³ is 109.28°, 120°, and 180° respectively. So the order will be

BeCl₂ > BCl₃ > CCl₄

Compare the bond angle in NO₂⁺ and NO₂⁻?

Check the hybridization for both NO₂⁺ and NO₂⁻.

Hybridization of NO₂⁺

Z = 1/2 (5 + 0 – 1 + 0)

Z = 1/2 (4)

Z = 2

sp hybridization (Bond angle = 180°)

Hybridization of NO₂⁻

Z = 1/2 (5 + 1 – 0 + 0)

Z = 1/2 (6)

Z = 3

sp² hybridization (Bond angle = 120°)

The order of bond angle is NO₂⁺ > NO₂⁻.

Compare the bond angle in CH₄, NH₃, and H₂O?

Calculate the hybridization of CH₄, NH₃, and H₂O.

Hybridization of CH₄

Z = 1/2 (4 + 0 – 0 + 4)

Z = 1/2 (8)

Z = 4

sp³ hybridization

Hybridization of NH₃

Z = 1/2 (5 + 0 – 0 + 3)

Z = 1/2 (8)

Z = 4

sp³ hybridization

Hybridization of H₂O

Z = 1/2 (6 + 0 – 0 + 2)

Z = 1/2 (8)

Z = 4

sp³ hybridization

We observe that the hybridization of CH₄, NH₃, and H₂O is the same, so the hybridization is not enough to determine the bond angle. Now move to the next step and check the lone pair on the central angle. How to find the lone pair?

Lone pair on the central angle = Z – number of surrounding atoms

Lone pair on CH₄

Lone pair = Z – no. of the surrounding atom

Lone pair = 4-4

Lone pair = 0

Lone pair on NH₃

Lone pair = Z – no. of the surrounding atom

Lone pair = 4-3

Lone pair = 1

Lone pair on H₂O

Lone pair = Z – no. of the surrounding atom

Lone pair = 4-2

Lone pair = 2

As we know that the more the lone pair on the central atom, the lesser the bond angle. So the order will be

CH₄ > NH₃ > H₂O

Remember the repulsion order:

lone pair-lone pair > lone pair-bond pair > bond pair-bond pair

Compare the bond angle in SO₃ and SO₂?

Check the Z value for both SO₃ and SO₂.

Hybridization of SO₃

Z = 1/2 (6 + 0 – 0 + 0)

Z = 1/2 (6)

Z = 3

sp² hybridization

Hybridization of SO₂

Z = 1/2 (6 + 0 – 0 + 0)

Z = 1/2 (6)

Z = 3

sp² hybridization

Hybridization is the same, now check the lone pair on the central atom.

• Lone pair on SO₃: Lone pair = 3-3 = 0
• Lone pair on SO₂: Lone pair = 3-2 = 1

The more the lone pair, the lesser will be the bond angle. So the order will be SO₃ > SO₂.

Compare the bond angle in NH₃ and PH₃?

Hybridization of NH₃

Z = 1/2 (5 + 0 – 0 + 3)

Z = 1/2 (8)

Z = 4

sp³ hybridization

Hybridization of PH₃

Z = 1/2 (5 + 0 – 0 + 3)

Z = 1/2 (8)

Z = 4

sp³ hybridization

Hybridization is the same, now check the lone pair on the central atom.

• Lone pair on NH₃: Lone pair = 4-3 = 1
• Lone pair on PH₃: Lone pair = 4-3 = 1

If the Z value and the lone pair on the central atom are the same, then move on to the next step to predict the bond angle. If the central angle is different and the surrounding atoms are the same then check the electronegativity of the central atom. The greater the electronegativity of the central atom, the greater will be the bond angle. The electronegativity of nitrogen is greater than phosphorus. So the order will be:

NH₃ > PH₃

Compare the bond angle in COF₂ and COCl₂?

Hybridization of COF₂

Z = 1/2 (4 + 0 – 0 + 2)

Z = 1/2 (6)

Z = 3

sp² hybridization

Hybridization of COCl₂

Z = 1/2 (4 + 0 – 0 + 2)

Z = 1/2 (6)

Z = 3

sp² hybridization

• Lone pair on COF₂: Lone pair = 3-3 = 0
• Lone pair on COCl: Lone pair = 3-3 = 0

If the central atom is the same and the surrounding atoms are different then check the electronegativity of the surrounding atoms. Thr greater the electronegativity of the surrounding atom, the lesser will be the bond angle. So the order will be COF₂ < COCl₂.

Test Yourself

Compare the bond angle in NO₃⁻, NO₂⁻ and NO₂⁺?

Compare the bond angle in NH₄⁺, NH₃ and NH₂⁻?

Compare the bond angle in H₂O, H₂S, H₂S, and H₂Te?

Compare the bond angle in SOF₂, SOCl₂, SOBr₂, and SOI₂?