Download C4S1 - The Development of Atomic Theory

Chapter 4: Atoms
Section 1: The Development of
Atomic Theory
Timeline of Atomic Models
• http://socratic.org/chemistry/a-closer-look-at-theatom/timeline-of-atomic-models
The Beginnings of Atomic Theory
• In the fourth century BCE, the Greek philosopher
Democritus suggested that the universe was made
by indivisible units
Dalton’s Atomic Theory
• According to Dalton, all atoms of a given element were
exactly alike, and atoms of different elements could join
to form compounds
Thomson’s Model of the Atom
• Thomson’s cathode-ray tube experiment suggested
that cathode rays were made negatively charged
particles that came from inside atoms
• Electron is a subatomic particle that has a negative
charge
Rutherford’s Model of the Atom
• Rutherford proposed that most of the mass of the
atom was concentrated at the atom’s center
• The nucleus is an atom’s central region, which is
made up of protons and neutrons