Atomic Theory: Democritus to Dalton

Democritus

• Lived around 460–370 BCE as a Greek philosopher.
• Introduced the concept that all matter is composed of indivisible particles called "atomos," meaning 'indivisible' in Greek.
• Proposed that continuous division of matter would eventually result in particles that cannot be divided any further.

John Dalton

• Developed Democritus's ideas in the early 1800s, over 2000 years later.
• English chemist known for advancing atomic theory through experimental results from earlier chemists.
• Proposed that matter consists of tiny particles termed atoms.

Dalton's Key Ideas

• Atoms cannot be created or destroyed; they are indivisible.
• All atoms of a single element are identical; atoms of different elements vary.
• Atoms maintain their identity when forming compounds.
• Compounds are formed by atoms in simple whole-number ratios. Example: hydrogen and oxygen combine in a 2:1 ratio to form water (H₂O).

Additional Concepts in Atomic Theory

• Particles are microscopic and not visible to the naked eye.
• Particle movement varies with temperature; particles move faster when hot and slower when cold.
• All particles possess mass.
• Particles can cluster to form larger structures; their masses combine when they do.
• There are spaces between individual particles.
• Forces exist between particles to maintain structure and prevent separation.

Significance

• Dalton's model paved the way for the field of chemistry by enhancing the understanding of atomic behavior in substances.
• The rules derived from particle behavior contribute to the fundamental principles explaining the nature of matter.