What is sp2 Hybridisation?

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Grade Level:

Class 12

AI/ML, Physics, Biotechnology, FinTech, EVs, Space Technology, Climate Science, Blockchain, Medicine, Engineering, Law, Economics

Definition

What is it?

sp2 hybridisation is a process where one 's' atomic orbital and two 'p' atomic orbitals mix together to form three new, identical hybrid orbitals called sp2 hybrid orbitals. These hybrid orbitals are arranged in a flat, triangular shape around the central atom, leading to a trigonal planar geometry.

Simple Example

Quick Example

Imagine you have three different types of snacks: one ladoo (s-orbital) and two jalebis (p-orbitals). When you mix them all up and reshape them, you get three completely new, identical snacks, let's say three different kinds of barfis (sp2 hybrid orbitals). These three barfis will then arrange themselves equally spaced on a plate, just like sp2 orbitals arrange themselves in a plane.

Worked Example

Step-by-Step

Let's understand sp2 hybridisation in a carbon atom, like in an ethene (C2H4) molecule.

1. **Ground State of Carbon:** A carbon atom in its ground state has electron configuration 1s^2 2s^2 2p^2. This means it has two electrons in the 2s orbital and two electrons in the 2p orbitals (one in 2px, one in 2py, 2pz is empty).
---2. **Excited State of Carbon:** To form more bonds, one electron from the 2s orbital gets promoted to the empty 2pz orbital. Now the configuration is 1s^2 2s^1 2px^1 2py^1 2pz^1. All four orbitals (one 2s and three 2p) now have one electron each.
---3. **Hybridisation:** For sp2 hybridisation, one 2s orbital and two 2p orbitals (say 2px and 2py) mix. The 2pz orbital remains unhybridised.
---4. **Formation of sp2 Hybrid Orbitals:** This mixing forms three new, identical sp2 hybrid orbitals. Each sp2 hybrid orbital has a 33.3% 's' character and 66.7% 'p' character.
---5. **Geometry:** These three sp2 hybrid orbitals arrange themselves as far apart as possible in a plane, forming bond angles of 120 degrees with each other. This results in a trigonal planar geometry.
---6. **Unhybridised p-orbital:** The remaining unhybridised 2pz orbital is perpendicular to the plane of the sp2 hybrid orbitals.

**Answer:** A carbon atom in ethene undergoes sp2 hybridisation, forming three sp2 hybrid orbitals and one unhybridised p-orbital, leading to a trigonal planar arrangement.

Why It Matters

Understanding sp2 hybridisation helps engineers design new materials with specific properties, like stronger plastics for car parts or lighter components for drones. In biotechnology, it helps understand how molecules interact, which is key for developing new medicines. Even in AI/ML, the principles of molecular structure, which hybridisation explains, can be used to model and predict properties of new compounds, accelerating drug discovery and material science.

Common Mistakes

MISTAKE: Thinking all 'p' orbitals participate in sp2 hybridisation. | CORRECTION: Only *two* 'p' orbitals mix with one 's' orbital to form sp2 hybrid orbitals. One 'p' orbital remains unhybridised.

MISTAKE: Believing sp2 hybrid orbitals are different in energy or shape. | CORRECTION: The core idea of hybridisation is that the new hybrid orbitals are *identical* in energy and shape, making bond formation more stable.

MISTAKE: Confusing the geometry of sp2 with sp or sp3. | CORRECTION: sp2 hybridisation always leads to a *trigonal planar* geometry with 120-degree bond angles, unlike the linear (sp) or tetrahedral (sp3) geometries.

Practice Questions

Try It Yourself

QUESTION: How many sp2 hybrid orbitals are formed when one s and two p orbitals hybridise? | ANSWER: Three sp2 hybrid orbitals are formed.

QUESTION: What is the bond angle expected between sp2 hybrid orbitals? | ANSWER: The bond angle expected is 120 degrees.

QUESTION: If a central atom undergoes sp2 hybridisation, what will be the geometry around that atom? Give an example of a molecule. | ANSWER: The geometry will be trigonal planar. An example is the carbon atom in ethene (C2H4) or the central boron atom in boron trifluoride (BF3).

MCQ

Quick Quiz

Which of the following molecules has a central atom undergoing sp2 hybridisation?

Methane (CH4)

Water (H2O)

Boron trifluoride (BF3)

Ammonia (NH3)

The Correct Answer Is:

Boron trifluoride (BF3) has a central boron atom bonded to three fluorine atoms with no lone pairs, resulting in a trigonal planar geometry, which is characteristic of sp2 hybridisation. Methane, water, and ammonia have sp3 hybridisation.

Real World Connection

In the Real World

sp2 hybridisation is crucial for understanding the structure of graphite, a form of carbon found in pencil lead. Each carbon atom in a graphite layer is sp2 hybridised, forming strong bonds with three other carbon atoms in a hexagonal pattern. The unhybridised p-orbitals overlap to form delocalised electron clouds, allowing graphite to conduct electricity, making it useful in batteries and electrodes for electric vehicles (EVs).

Key Vocabulary

Key Terms

ORBITAL: A region around the nucleus where electrons are most likely to be found. | HYBRIDISATION: The mixing of atomic orbitals to form new, identical hybrid orbitals. | TRIGONAL PLANAR: A molecular geometry where a central atom is bonded to three other atoms, all lying in the same plane with 120-degree angles. | UNHYBRIDISED ORBITAL: An atomic orbital that does not participate in hybridisation and retains its original shape and energy.

What's Next

What to Learn Next

Great job understanding sp2 hybridisation! Next, you should explore 'sp3 Hybridisation'. It builds on the same concepts but involves a different number of orbitals mixing, leading to a different molecular shape, which is super important for understanding many common organic molecules.