Study Notes for CHEN 1201 - General Chemistry for Engineers - 34

GENERAL CHEMISTRY FOR ENGINEERS

Course Information

  • Course Title: General Chemistry for Engineers

  • Course Code: CHEN 1201

  • Instructor: Carolyn Kohlmeier

  • Department: Chemical and Biological Engineering

Week 13 Lecture Overview

Lecture 34 Topics

  1. Topics from Last Lecture

    • VSEPR Theory

    • Polar Molecules

    • Valence Bond Theory

  2. Topics for Today

    • Continued exploration of Valence Bond Theory

    • Introduction to Orbital Hybridization

Polar Molecules and Reactivity

Question on Polar Molecules

  • Consider the molecules:

    • PCl₅

    • COS

    • XeO₃

  • How many of these molecules are polar?

    • Options: A. 0 B. 1 C. 2 D. 3

Further Question on Polar Molecules

  • Considering the molecules:

    • BrCl₃

    • CS₂

    • SO₃

  • Which of these are polar?

    • Options: A. BrCl₃ B. CS₂ C. SO₃ D. Both BrCl₃ and SO₃ E. CS₂ and SO₃

  • Electron Count:

    • BrCl₃: 28 electrons

    • CS₂: 16 electrons

    • SO₃: 24 electrons

Valence Bond Theory

Core Principles of Valence Bond Theory

  • Valence electrons of atoms in molecules reside in quantum mechanical orbitals:

    • Standard orbitals (s, p, d, f )

    • Hybrid orbitals

  • A chemical bond results from the overlap of two half-filled orbitals.

  • The geometry of the overlapping orbitals determines the resulting molecular geometry.

Orbital Hybridization

Hybridization of Orbitals

  • Hybridization Explanation:

    • Involves the combination of atomic orbitals to form new hybrid orbitals that are suitable for the pairing of electrons to form chemical bonds.

  • SP³ Hybrid Orbitals:

    • Four sp³ hybrid orbitals are formed from one s orbital and three p orbitals.

    • Each hybrid orbital has two lobes, oriented towards the corners of a tetrahedron at an angle of 109.5°.

Representation of Hybridization and Molecular Geometry

  • Hybridization Visualization:

    • Each sp³ hybrid orbital can form bonds:

    • Example structure:

    • Four hydrogen 1s atomic orbitals overlap with four carbon sp³ hybrid orbitals in Methane (CH₄).

    • Each C-H bond forms through head-on overlap of a singly occupied sp³ hybrid orbital and a hydrogen 1s orbital.

Other Hybridization Types

SP² Hybridization

  • Characteristics:

    • An sp² hybrid orbital consists of two lobes, one larger than the other.

    • Hybrid orbitals in sp² position themselves in a plane at angles of 120°.

    • One unhybridized p orbital remains, perpendicular to the plane of sp² hybrids.

Example of sp² Hybridization: Sulfur in SF₂

  1. Lewis Structure Drawing

    • Example: F - S - F

  2. Electron Group Counting:

    • Total of 4 electron groups.

    • Resulting Hybridization: sp³.

Multiple Bonds and Hybridization

π Bonding Description

  • Double Bond: Consists of one σ bond and one π bond.

  • Triple Bond: Comprises one σ bond and two π bonds.

Double Bond Example: Ethene (C₂H₄)

  • Structure:

    • H
      C=C

    • H

  • Hybridization:

    • C atoms are sp² hybridized.

    • Overlap of two unhybridized p orbitals results in π bonding.

Triple Bond Example: Ethyne (C₂H₂)

  • Structure:

    • H - C≡C - H

  • Bonds Description:

    • Involves one σ bond (formed from sp-sp overlap) and two additional π bonds.

Molecule Example: H₃O⁺

Determining Hybridization of Oxygen

  1. Lewis Structure Creation:

    • H - O - H (with lone pair on O)

  2. Determine Electron Angle:

    • Approximate angle is 107° due to lone pair effects.

Sigma and Pi Bonds in Benzene (C₆H₆)

Number of Bonds Calculation

  • Consider options:

    • A. 3 sigma bonds, 6 pi bonds

    • B. 6 sigma bonds, 6 pi bonds

    • C. 6 sigma bonds, 3 pi bonds

    • D. 12 sigma bonds, 3 pi bonds

    • E. 15 sigma bonds, 3 pi bonds

Hybridization of Central Atom in NO₂⁻

  • Determine hybridization:

    • Options:

    • A. sp

    • B. sp²

    • C. sp³