Notes-(01)
| Site: | Prefrontal Learning Center |
| Course: | Hybridization |
| Book: | Notes-(01) |
| Printed by: | Guest user |
| Date: | Friday, 20 September 2024, 8:06 AM |
Description
(d) describe sp3 hybridisation, as in ethane molecule, sp2 hybridisation, as in ethene and benzene molecules, and sp hybridisation, as in ethyne molecule
(e) explain the shapes of, and bond angles in, the ethane, ethene, benzene, and ethyne molecules in relation to σ and π carbon-carbon bonds
1. Ground State of Carbon Atom
Note: Be Able to Construct Diagram
01 Multiple Choice
1.1. Bonding Limitation (Theoretically but not empirically true)
Carbon atom
o Out of the 4 valence electrons
o Only 2 are unpaired and available for bonding (located in the \(2p_x\) and \(2p_y\) orbitals)
01 Multiple Choice
2. Carbon Bonding in Organic Compounds
However, we would not be able to explain why carbon almost always forms 4 bonds, for example in the following compounds:
| Methane \((CH_4)\) | 4 \(C-H\) single bonds |
| Ethene \((CH_2=CH_2)\) |
Each carbon atom has o 1 \(C=C\) (double bond) o 2 \(C-H\) single bonds |
| Ethyne \((H-C≡C-H)\) |
Each carbon atom has |
Hence we need to introduce the concept of hybridisation to help us account for the bonding issues here
2.1. Excited State of Carbon Atom
One of the 2s electron in C atom is promoted into the 2p orbital
Note: Be Able to Construct Diagram
01 Multiple Choice
2.2. Types of Hybridisation in Carbon
o Hybridisation refers to the mixing of atomic orbitals in an atom (usually the central atom) to generate a new set of orbitals called hybrid orbitals.
The C atom can undergo three types of hybridisation:
(a) \(sp^3\) hybridization (e.g. in methane)
(b) \(sp^2\) hybridization (e.g. in ethene and benzene)
(c) \(sp\) hybridization (e.g. in ethyne) benzene
3. sp3 Hybridization
3.2. Shape and Bond Angle
o Electrons repel one another
o \(sp^3\) hybrid orbitals are placed as far apart as possible
Shape: Tetrahedral
Bond Angle (Around C): 109.5°
4. sp2 Hybridization
4.1. Hybridization
Note: Be Able to Construct Diagram
01 Multiple Choice
4.2. Shape and Bond Angle
o Electrons repel one another
o \(sp^2\) hybrid orbitals are placed as far apart as possible
Shape: Trigonar planar
Bond Angle (Around C): 120°
5. sp Hybridisation
5.1. Hybridisation
Note: Be Able to Construct Diagram
01 Multiple Choice
5.2. Shape and Bond Angle
o Electrons repel one another thus the \(sp\) hybrid orbitals are placed as far apart as possible by adopting the linear arrangement
Shape: Linear
Bond Angle (Around C): 180°
6. Number of σ bond(s) and π bond(s)
6.2. Sigma (σ) bond | Ethane
 |
 |
| Bond type | Number of bonds |
| σ Bonds | 7 |
| π Bonds | 0 |
6.3. Sigma (σ) bond and Pi (π) bond | Ethene
| Sigma(σ) bond | (a): Five σ bonds o One C–C bond: Overlap of sp2 hybrid orbitals on the carbon atom with one sp2 hybrid orbital on the other carbon atom o Four C–H bonds: Overlap between the C atoms’ sp2 orbitals with s orbitals on the hydrogen atoms |
| Pi(π) bond | (b): One π bond o Formed by the side-by-side overlap of unhybridized p orbitals on each carbon atom o Two lobes of the π bond are above and below the plane of the σ system |
6.4. Sigma (σ) bond and Pi (π) bond | Ethyne
| Sigma(σ) bond | (a): Three σ bonds o One C–C bond: Overlap of sp2 hybrid orbitals on the carbon atom with one sp2 hybrid orbital on the other carbon atom o Two C–H bonds: Overlap between the C atoms’ sp2 orbitals with s orbitals on the hydrogen atoms |
| Pi (π) bond | (b): Each of the two π bonds o Formed by the side-by-side overlap of unhybridized p orbitals on each carbon atom o Two lobes of the π bond are above and below the plane of the σ system o Two lobes of each π bond are positioned across from each other around the line of the C–C σ bond |