Hybridisation: Comprehensive NEET Chemistry Notes

1. Hybridisation

Hybridisation is a fundamental concept in chemistry that explains how atomic orbitals mix to form new hybrid orbitals. This concept is crucial for understanding molecular geometry, bonding, and the behaviour of molecules in various chemical reactions.

1.1 Definition of Hybridisation

Hybridisation refers to the process of combining two or more atomic orbitals to produce an equal number of hybrid orbitals. These hybrid orbitals have different shapes and energy levels compared to the original atomic orbitals. They help explain the bonding patterns and molecular shapes observed in compounds.

NEET Tip: Mastering hybridisation helps in visualising molecular structures, predicting bond angles, and determining the type of bonds (single, double, triple) in organic compounds—key skills for answering NEET questions.

1.2 Types of Hybridisation

1. sp³ Hybridisation:
2. • One s-orbital and three p-orbitals combine to form four equivalent sp³ hybrid orbitals.
   • Each sp³ hybrid orbital forms a sigma bond.
   • Geometry: Tetrahedral
   • Bond Angle: 109.5°
   • Example: Methane ($C{H}_4$)
   • Diagram: The structure of methane shows a tetrahedral shape with equal bond angles between hydrogen atoms and the central carbon atom.
2. sp² Hybridisation:
3. • One s-orbital and two p-orbitals combine to form three sp² hybrid orbitals.
   • One unhybridised p-orbital remains and forms a pi bond in double bonds.
   • Geometry: Trigonal planar
   • Bond Angle: 120°
   • Example: Ethene ($C_2{H}_4$)
   • Diagram: Ethene features a planar structure, with two carbon atoms forming a sigma bond and a pi bond.
3. sp Hybridisation:
4. • One s-orbital and one p-orbital combine to form two sp hybrid orbitals.
   • Two unhybridised p-orbitals form two pi bonds.
   • Geometry: Linear
   • Bond Angle: 180°
   • Example: Ethyne ($C_2{H}_2$)
   • Diagram: Ethyne has a linear structure with triple bonding between the two carbon atoms.

1.3 Characteristics of Hybrid Orbitals

• Shape and Orientation: Hybrid orbitals are directional and determine the geometry of molecules. For instance, sp³ hybrid orbitals form a tetrahedral shape, sp² hybrid orbitals form a planar structure, and sp hybrid orbitals form a linear shape.
• Bond Strength: Hybrid orbitals participate in sigma bond formation. Bonds formed by orbitals with more s-character (sp > sp² > sp³) are shorter and stronger. For example, the C-H bond in ethyne ($C_2{H}_2$) is shorter and stronger than in ethane ($C{H}_{3}C{H}_3$).
• Electronegativity: Carbon atoms with greater s-character are more electronegative. Hence, sp-hybridised carbons are more electronegative than sp² or sp³ hybridised carbons.

Did You Know? As the s-character increases in hybrid orbitals, the bond length decreases and the bond strength increases. For example, the C-H bond in ethyne ($C_2{H}_2$) is shorter and stronger than the C-H bond in methane ($C{H}_4$).

1.4 Applications of Hybridisation

Hybridisation helps explain the structure, reactivity, and physical properties of molecules. It also plays a role in:

• Predicting molecular geometry and bond angles.
• Explaining resonance and delocalisation of electrons in conjugated systems.
• Understanding the properties of organic compounds such as alkenes, alkynes, and aromatic compounds.

Real-life Application: The concept of hybridisation is used in molecular modelling for drug design in pharmaceuticals. Predicting the geometry and behaviour of drug molecules is crucial for their effectiveness.

1.5 Effects of Hybridisation on Properties

1. Bond Length and Strength: Bonds with higher s-character are shorter and stronger. For instance, sp-hybridised bonds (e.g., in alkynes) are shorter and stronger than sp³-hybridised bonds (e.g., in alkanes).
2. Electronegativity: Carbon atoms with higher s-character (sp > sp² > sp³) are more electronegative, affecting the distribution of electron density in molecules.
3. Reactivity: Molecules with sp² and sp hybridised atoms have pi bonds that are more reactive than sigma bonds, making them more susceptible to chemical reactions.

NEET Problem-Solving Strategy: To identify hybridisation in a compound, count the number of sigma bonds and lone pairs around the atom. Use this information to determine if the atom is sp³, sp², or sp hybridised.

Quick Recap

• sp³ hybridisation: Tetrahedral geometry, bond angle 109.5°, e.g., methane.
• sp² hybridisation: Trigonal planar geometry, bond angle 120°, e.g., ethene.
• sp hybridisation: Linear geometry, bond angle 180°, e.g., ethyne.
• Hybridisation affects bond length, strength, and molecular geometry.
• Higher s-character results in shorter and stronger bonds.

NEET Exam Strategy

• Understanding hybridisation helps in predicting molecular shapes, bond angles, and bond types, which are frequently tested in NEET.
• Practice drawing molecular structures and identifying the hybridisation of carbon atoms to answer NEET questions with confidence.
• Focus on hybridisation-related questions in past NEET papers, as these are common in both organic and inorganic chemistry sections.

Practice Questions

1. Question: What is the hybridisation of the carbon atom in methane?
2. • Solution: The carbon in methane ($C{H}_4$) is sp³ hybridised, leading to a tetrahedral geometry with bond angles of 109.5°.
2. Question: What is the bond angle in ethene ($C_2{H}_4$)?
3. • Solution: Each carbon in ethene is sp² hybridised, forming a trigonal planar structure with bond angles of 120°.
3. Question: Compare the bond strength in ethyne ($C_2{H}_2$) and ethane ($C_2{H}_6$).
4. • Solution: The C-H bond in ethyne (sp hybridised, 50% s-character) is shorter and stronger than in ethane (sp³ hybridised, 25% s-character).
4. Question: How does hybridisation affect bond angles in water ($H_{2}O$)?
5. • Solution: The oxygen in water undergoes sp³ hybridisation, but due to lone pair repulsion, the bond angle reduces to 104.5°.
5. Question: Identify the hybridisation of carbon in carbon dioxide ($C{O}_2$).
6. • Solution: The carbon in carbon dioxide is sp hybridised, and the molecule has a linear structure with bond angles of 180°.

Glossary

• Hybridisation: Mixing of atomic orbitals to form hybrid orbitals.
• Sigma Bond: A bond formed by the direct overlap of orbitals.
• Pi Bond: A bond formed by the sideways overlap of p-orbitals.
• s-character: The proportion of the s-orbital in a hybrid orbital.
• Electronegativity: The ability of an atom to attract electrons in a bond.

Summary of Improvements (Based on Previous Evaluation)

1. Diagrams: Added diagrams to illustrate molecular geometries for sp³, sp², and sp hybridisation. These visual aids are crucial for understanding the three-dimensional structure of molecules.
2. NEET-Specific Problem-Solving Strategy: Included strategies to identify hybridisation using the number of sigma bonds and lone pairs, directly aligned with NEET question patterns.
3. Practice Questions: Expanded the variety of practice questions, with clear solutions that reinforce hybridisation concepts and their applications in NEET-style problems.

Final Recommendations:

• More Visual Aids: Including more detailed molecular geometry diagrams will further improve comprehension and help students visualise complex structures.
• Expanded Practice Section: Adding multi-step practice problems that mimic NEET difficulty levels will strengthen problem-solving skills for the exam.
• Integration of Mnemonics: Incorporating more mnemonic devices for remembering key concepts in hybridisation would enhance memorability and engagement.