I. Definitions:

A. Structural Formula:

Shows the arrangement of atoms in a compound.

B. Molecular Formula:

Shows the number of atoms of each element in a compound.

II. Example:

n-Butane
- Structural formula: CH₃-CH₂-CH₂-CH₃
- Molecular formula: C₄H₁₀

III. Steps to Write Molecular Formula from Structural Formula:

1. Identify different types of elements in the structural formula.
2. Write symbols of these elements side by side.
3. Count the number of atoms of each element.
4. Show this number as subscripts for each element symbol.

IV. Example 6.13: Writing the Molecular Formula

Given structural formula: CH₃-CH₂-CH₂-OH
Molecular formula: C₃H₈O

V. Practice Exercise:

• Write molecular formulae for:
  • CH₃-CH₂-OH
  • CH₃-CH₂-NH₂
  • CH₃-CO-CH₃

VI. Key Points:

• Chemistry: Science of materials of the universe
• Physical Chemistry: Deals with laws and theories of matter structure and changes
• Element: Substance with atoms of the same atomic number
• Compound: Two or more elements in fixed proportions held by chemical bonds
• Empirical Formula: Simplest whole-number ratio of atoms in a compound
• Molecular Formula: Exact number of atoms in a molecule
• Molecular Mass: Sum of atomic masses of all atoms in a molecule
• Avogadro's Number: Number of particles in one mole of a substance
• Mole: Amount of matter containing Avogadro's number of particles
• Gram Atomic Mass: Atomic mass in grams
• Gram Molecular Mass: Molecular mass in grams
• Gram Formula Mass: Formula mass in grams