3.7.1 sp Hybridization

This topic explains sp hybridization — the mixing of one s orbital and one p orbital to form two new hybrid orbitals. It covers the definition, examples, and bond angles.

Definition

sp hybridization is the mixing of one s and one p orbital to form two sp hybrid orbitals of equal energy and shape.

Key Features

• Two sp hybrid orbitals are formed.
• They are arranged linearly at 180°.
• Each has 50% s-character and 50% p-character.
• They form sigma bonds only.

Example: BeCl₂

• Ground state of Be: 1s² 2s²
• Excitation: 1s² 2s¹ 2p¹
• Hybridization: 2s + 2p → 2 sp orbitals
• sp orbitals overlap with Cl p orbitals
• Shape: Linear
• Bond angle: 180°

Example: C₂H₂ (Acetylene)

• Ground state of C: 1s² 2s² 2p_x¹ 2p_y¹
• Excitation: 1s² 2s¹ 2p_x¹ 2p_y¹ 2p_z¹
• Hybridization: 2s + 2p → 2 sp orbitals
• sp orbitals form sigma bonds
• Unhybridized p orbitals form pi bonds
• Shape: Linear

Main Idea

In sp hybridization, one s orbital and one p orbital mix to form two sp hybrid orbitals. These orbitals are arranged linearly at 180° to each other. Each sp hybrid orbital has 50% s-character and 50% p-character. The sp hybrid orbitals can form only sigma bonds by overlapping with other atomic orbitals.

Core Concept

sp hybridization occurs when a central atom needs to form two bonds and has no lone pairs. The two sp hybrid orbitals point in opposite directions (180° apart), giving a linear geometry.

Detailed Explanation

What is sp Hybridization?

• The intermixing of one s and one p orbital of different energies and different shapes.
• Produces two new hybrid orbitals of the same energy and same shape.
• Each sp hybrid orbital has 50% s-character and 50% p-character.
• The sp hybrid orbitals can form only sigma bonds by overlapping with other atomic orbitals.

Example 1: Beryllium Chloride (BeCl₂)

• Ground state: 1s² 2s²
• There are no unpaired electrons in the ground state.

• Beryllium undergoes excitation by promoting one of its 2s electrons into an empty 2p orbital.
• Excited state configuration: 1s² 2s¹ 2p¹

• In the excited state, the beryllium atom undergoes sp hybridization by mixing a 2s and one 2p orbital.
• One electron from 2s orbital is promoted to 2p to form two new hybridized orbitals.
• These hybrid orbitals are arranged linearly at 180°.

• The two beryllium sp hybrid orbitals overlap with p orbitals of chlorine atoms.
• The bonding is shown in the figure.
• Thus, BeCl₂ is linear in shape with a bond angle of 180°.

Example 2: Acetylene (C₂H₂)

• Ground state: 1s² 2s² 2p_x¹ 2p_y¹
• There are only two unpaired electrons in the ground state.
• However, the valency of carbon is four — it forms 4 bonds.
• To form four bonds, there must be four unpaired electrons.

• Carbon promotes one of its 2s electrons into the empty 2p orbital in the excited state.
• Excited state configuration: 1s² 2s¹ 2p_x¹ 2p_y¹ 2p_z¹

• Each carbon atom undergoes sp hybridization by using a 2s and one 2p orbital in the excited state.
• This gives two half-filled sp orbitals, which are arranged linearly.

• The two carbon atoms form a sigma bond with each other using sp hybrid orbitals.
• A pi bond is also formed between them due to the parallel overlapping of unhybridized 2p orbitals.
• Each carbon atom also forms a sigma bond between its sp orbital and the s orbital of a hydrogen atom.

• Acetylene has a triple bond between the two carbon atoms (one sigma + two pi).
• The molecule is linear.

Summary of sp Hybridization

Important Points

• 1. sp hybridization = mixing of one s and one p orbital.
• 2. Two sp hybrid orbitals are formed.
• 3. They are arranged linearly at 180°.
• 4. Each has 50% s-character and 50% p-character.
• 5. They form sigma bonds only.
• 6. Example: BeCl₂ (linear), C₂H₂ (linear, triple bond).
• 7. In C₂H₂, unhybridized p orbitals form pi bonds.

Remember

• - sp hybridization: 1 s + 1 p → 2 sp orbitals
• - Geometry: Linear
• - Bond angle: 180°
• - s-character: 50%
• - p-character: 50%
• - Bonds: Sigma only
• - Examples: BeCl₂, C₂H₂

Common Mistakes

• 1. Thinking sp hybridization gives bent shape: It gives linear shape.
• 2. Forgetting the 50% s and 50% p character: Each sp orbital has 50% s and 50% p.
• 3. **Confusing sp with sp² or sp³:** sp = 1 s + 1 p; sp² = 1 s + 2 p; sp³ = 1 s + 3 p.
• 4. Ignoring pi bonds in C₂H₂: The unhybridized p orbitals form pi bonds.

Quick Revision

• sp hybridization = mixing of one s and one p orbital.
• Two sp hybrid orbitals are formed.
• They are arranged linearly at 180°.
• Each has 50% s-character and 50% p-character.
• They form sigma bonds only.
• Example: BeCl₂ (linear), C₂H₂ (linear, triple bond).
• In C₂H₂, unhybridized p orbitals form pi bonds.

60-Second Revision

• sp hybridization: 1 s + 1 p → 2 sp orbitals
• Geometry: Linear
• Bond angle: 180°
• s-character: 50%
• p-character: 50%
• Bonds: Sigma only
• Examples: BeCl₂, C₂H₂

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• Topic: 3.7.1 sp Hybridization
• Chapter: 3 (Chemical Bonding)

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