Ch01_ Lecture Modified by B. Lavey

Organic Chemistry Overview

• Textbook: Organic Chemistry, Fourth Edition by Janice Gorzynski Smith

  • Institution: University of Hawai’i

  • Prepared by: Layne A. Morsch, University of Illinois - Springfield

  • Copyright: The McGraw-Hill Companies, Inc.

Atomic Structure

Nucleus and Electron Cloud

• Nucleus: Contains positively charged protons and uncharged neutrons.

• Electron Cloud: Composed of negatively charged electrons.

Key Definitions

• Atomic Number: Number of protons in the nucleus; equals the number of electrons in a neutral atom.

• Atomic Mass: Total number of protons plus neutrons (e.g., Carbon-12 has 6 protons and 6 neutrons).

Ions

Cations and Anions

• Cation: Positively charged atom with fewer electrons than protons.

• Anion: Negatively charged atom with more electrons than protons.

Isotopes

• Definition: Atoms of the same element that have different numbers of neutrons.

• Example: Most carbon has 6 neutrons, but 1.1% has 7 neutrons.

The Periodic Table

Element Properties

• Rows (Periods): Elements are similar in size.

• Columns (Groups): Elements in the same column have similar electronic and chemical properties.

Atomic Orbitals

Types of Orbitals

• s Orbital: Sphere of electron density; lower energy than p orbitals.

• p Orbital: Dumbbell shape; higher energy than s orbital with a node at the nucleus.

Orbital Capacity

• First Shell: One s orbital; holds a maximum of 2 electrons (H and He).

• Second Row: Contains 2s and 2p orbitals available for bonding and accommodating up to eight electrons.

Bonding

Types of Bonds

• Ionic Bonds: Result from electron transfer, typically between elements from opposite sides of the periodic table.

• Covalent Bonds: Formed by sharing electrons between atoms of similar electronegativity.

Bonding Principles

• To achieve a stable electron configuration (octet), atoms can form either ionic or covalent bonds.

Lewis Structures

Drawing Lewis Structures

• Steps to Draw:

  1. Arrange atoms next to each other.

  2. Count valence electrons and adjust for charges.

  3. Connect atoms with bonds, ensuring octets are filled.

  4. Assign formal charges.

Resonance Structures

• Definition: Different arrangements of electrons for the same molecular formula, represented by double-headed arrows.

• Resonance Hybrid: A composite representation reflecting delocalization of electrons over multiple atoms.

Molecular Geometry

Determining Geometry

• Factors Influencing Shape: Bond length and bond angle, based on VSEPR theory.

• Geometry Examples:

  • Linear: 2 groups around an atom.

  • Trigonal Planar: 3 groups around an atom, 120° apart.

  • Tetrahedral: 4 groups around an atom, 109.5° apart.

Bond Length and Strength

• Generally, bond length decreases and bond strength increases with the number of electrons between two nuclei; triple bonds are shorter and stronger than double bonds.

Electronegativity

• Definition: A measure of an atom's attraction for electrons in a bond.

• Bond Polarity:

  • Nonpolar bonds have equal sharing.

  • Polar bonds have unequal sharing based on electronegativity differences.

Summary of Concepts

Major Takeaways

• Understanding atomic structure, bonding types, orbital hybridization, and molecular geometry is crucial for mastering organic chemistry principles.

• Practice drawing Lewis structures, determining molecular shapes using VSEPR, and recognizing bond types based on electronegativity.

• Familiarize yourself with resonance structures for stability insights and geometric representations for accurate molecular modeling.