Atomic Structure

Chapter 3: Atoms

• Focuses on atomic theory and structure

Historical Context of Atomic Theory

Early Ideas

• 400 B.C.E.: Democritus proposed the term "atomos" meaning "indivisible" as the fundamental particle of matter.

Law of Conservation of Mass

• Proposed by Antoine Lavoisier (1743-1794)

  • In chemical reactions, matter is neither created nor destroyed.

  • Example: Hydrogen (4.0 g) + Oxygen (32.0 g) = Water (36.0 g)

John Dalton's Atomic Theory (1803-1877)

• Elements are composed of tiny, indivisible particles called atoms.

• Unique atoms for each element.

• Atoms can combine in whole-number ratios to create compounds.

• Atoms remain unchanged during chemical reactions.

Structure of Atoms

Uniqueness of Atoms

• Every element has distinct atoms.

Compounds Formation

• Atoms combine in whole-number ratios.

• Conservation of atoms in chemical reactions.

Subatomic Particles

• Basic components of atoms:

  • Electrons: negatively charged particles.

  • Protons: positively charged particles; mass = 1.0073 u.

  • Neutrons: neutral particles; mass = 1.0087 u.

Historical Developments in Chemistry

1800: Key Milestone in Chemistry

• Volta invents the electrochemical cell (battery).

Atomic Models

Plum Pudding Model

• Proposed by J.J. Thomson

  • Electrons spread throughout a positively charged material.

Rutherford's Findings

• Conducted experiments leading to the conclusion that:

  • The atom consists mostly of empty space.

  • A dense positively charged nucleus exists at the center of the atom.

Composition of the Atom

Atomic Identity

• The identity of an atom is determined by the number of protons:

  • 1 proton = Hydrogen

  • 2 protons = Helium

  • 3 protons = Lithium

  • 4 protons = Beryllium