Topic 1

ORGANIC CHEMISTRY: A Review of General Chemistry

Overview of Study Material

• A review emphasizing the following key topics from general chemistry:

  • Atoms

  • Atomic Orbitals (s, p, d)

  • The Periodic Table

  • Valence Electrons and Nonbonded Electrons

  • Electron Configuration

  • Bonding (Ionic and covalent)

  • Electronegativity

  • Bond Polarity (polar & non-polar)

  • The Octet Rule (especially for second-row elements, exceptions)

  • Lewis Structures

  • Calculation of Formal Charge

  • Resonance

  • Molecular Geometry

  • Hybridization

Understanding Organic Chemistry

• Definition of Organic Chemistry: The study of carbon-containing molecules and their reactions.

• Reaction Dynamics:

  • Molecules can collide during a reaction.

  • Bonds can be broken in the process.

  • New bonds can be made.

Importance of Organic Compounds

• Organic compounds are ubiquitous in:

  • Food

  • Clothes

  • Plastics

  • Pharmaceuticals

  • All living organisms

Atomic Structure

• Key Components:

  • Nucleus includes Protons (positively charged) and Neutrons (neutral).

  • Electrons (negatively charged) reside in orbitals outside the nucleus.

  • Focus is on valence electrons (outermost shell) as these are involved in bonding.

• Important Relationships:

  • Number of protons = atomic number

  • Number of neutrons = atomic mass - atomic number

Bond Formation

• Atoms unite through bonds:

  • Covalent Bond: Formed by sharing a pair of electrons between two atoms—demonstrated by two hydrogen atoms combining.

• Forces in Bond Formation:

  • Attractive forces between positively charged nuclei and negatively charged electrons.

  • Repulsive forces between:

  • Two positively charged nuclei.

  • Two negatively charged electrons.

Structural Theory of Matter

• Mid-1800s: Introduction of the idea that substances have a specific arrangement of atoms.

• Importance of Connectivity:

  • Two compounds can share the same molecular formula (e.g., C2H6O) but differ in their connectivity, known as constitutional isomers.

Drawing Constitutional Isomers

1. Determine the valency of each atom in the molecular formula.

2. Connect atoms of the highest valency first.

3. Place monovalent atoms at the perimeter.

4. Explore alternative atom connections (e.g., drawing isomers for C3H8O).

Counting Valence Electrons

• Valence Electrons can be determined using the periodic table.

• Valence electrons per atom based on group number:

  • Carbon (C): 4

  • Hydrogen (H): 1

  • Oxygen (O): 6

  • Nitrogen (N): 5

  • Halogens (F, Cl, Br, I): 7

Lewis Dot Structure of an Atom

• Lewis Dot Structure: Representation using dots around atomic symbols to depict valence electrons.

• Drawing Process:

  1. Each valence electron is represented as a dot.

  2. Initially, place one dot on each side of the atomic symbol.

  3. Pair electrons only after all sides have one dot.

  4. Max two dots per side.

• Example Atoms:

  • Beryllium (Be) - Lewis structure shown

  • Carbon (C) - Lewis structure shown

  • Nitrogen (N) - Lewis structure shown

  • Oxygen (O) - Lewis structure shown

Octet Rule and Covalent Bonding

• General bonding rule stating atoms form bonds to gain eight valence electrons (octet).

• Second-row elements (C, N, O, F) generally obey the Octet Rule:

  • Carbon: 4 valence electrons, needs