Chapter 4: Atoms

Section 1: The Development of Atomic Theory

Timeline of Atomic Models http://socratic.org/chemistry/a-closer-look-at-the-atom/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