Structure and Bonding 2

PHAR201 "Structure & Bonding"

  • Instructor: Dr. Mohamed Salah

  • Contact: M.Salah@ngu.edu.eg

Hybridization

  • Concept of hybridization is introduced.

Bonding – Bonding in Carbon

  • A 2s electron is promoted to an empty 2p orbital.

  • Combination of 2s and three 2p orbitals results in hybridization.

Bonding – sp3 Hybridisation

  • Why “sp3”?

  • Mixture of one s orbital and three p orbitals.

  • Shape: mixture of spherical s and dumbbell-shaped p orbitals.

  • All four orbitals (1s + 3p) are identical.

Bonding – sp3 Hybridisation (3D Arrangement)

  • Arrangement in 3D space aims to maximize distance between orbitals.

  • Forms a tetrahedral shape with bond angles of 109.5 degrees.

Bonding – Bonding in Methane

  • Covalent bonds in methane are formed through:

    • Each orbital having one electron.

    • Overlap between 1s orbital of hydrogen and sp3 orbital of carbon.

    • This results in sigma (σ) bonds, establishing the tetrahedral basis of chirality.

Methane Statements Quiz

  • Which statement about methane is FALSE?

    • A. All bond angles are 109.5°

    • B. Carbon atom is sp3 hybridized.

    • C. Molecule contains 4 σ-bonds.

    • D. Each atom has a closed-shell configuration.

    • E. Each hydrogen atom is sp3 hybridized.

Bonding - Bonding in Ethane

  • Structure involves sp3 carbon atoms with sp3-sp3 bonds.

  • Ethane characterized by:

    • H–C–C–H configuration.

    • Bond distance: 154 pm.

    • The bond angles in ethane are 111.2%.

Bonding – Multiple Bonds

  • More than two electrons can be shared in bonds:

    • Double bond: sharing four electrons (two pairs).

    • Triple bond: sharing six electrons (three pairs).

    • Bonds still maintain closed-shell configurations.

Bonding – sp2 Hybridisation

  • Why “sp2”?

    • Mixture of one s orbital and two p orbitals.

    • Shape is a mixture of spherical s and dumbbell-shaped p orbitals.

    • All three orbitals are identical.

Bonding – sp Hybridisation

  • Why “sp”?

    • Mixture of one s orbital and one p orbital.

    • Identical shape combining spherical s and dumbbell-shaped p.

Bonding - Polarity

  • Electronegativity:

    • Elements like O, N, F (and Cl) are highly electronegative.

  • Unequal sharing of electrons leads to polar covalent bonds.

    • Example: Hydrogen fluoride demonstrates this.

Bonding – Polar Bonds

  • Polarity is observed through:

  • Dipoles (two poles).

  • Differentiation between non-polar and polar molecules.

Bonding - Polarity Overview

  • Electronegativity Comparison:

    • Ionic vs. covalent bonding illustrated through differences in charge distribution.

  • Types of bonds ranked by ionic character:

    • Ionic bond > polar covalent bond > covalent bond.

Lewis Structure Comparison: H2O vs. H2S

  • Key similarities and differences include:

    • Electronic configuration and polarity among others.

Bonding – Overall Polarity

  • Assess net polarity by considering contributions from all bonds.

    • Example: Tetrachloromethane is non-polar, while water is highly polar.

Bonding – Relative Polarity Scale

  • Understanding overall molecular structure is critical:

    • Non-polar, weakly polar, and highly polar scale.

Bonding – Example One: Drug Delivery

  • Importance of polarity in drug delivery:

    • Role of polarity at the blood-brain barrier.

    • Anti-histamines categorized by polarity levels.

Neurotransmitter Polarity Ranking Activity

  • Rank three neurotransmitters in increasing polarity.

  • Options include: A, B, C, D, E.

Bonding – Example Two: Formulation

  • The role of polarity in drug solubility is crucial:

    • Highly polar drugs show good solubility in water;

    • Low polarity drugs exhibit poor solubility.

Recommended Reading

  • Textbook: McMurry, J.

  • Title: Organic Chemistry, 9th edition (2019)

  • Publisher: Brooks/Cole, Cengage Learning, CA 94002-3098

  • Content Available: Chapter 2 in library & soft copy provided.