01 Atomic Theory
Investigating Atoms and Atomic Theory
Learning Goals:
Describe the particle theory of matter.
Use the Bohr model to differentiate between protons, neutrons, and electrons, including their charges, relative masses, and locations.
Compare the Bohr atomic model to the electron cloud model regarding accuracy in representing atomic structure.
Historical Context of Atomic Theory
Term "Atomos": Meaning "not to be cut," coined by Democritus.
Atomic Models Overview
Bohr Model:
Nucleus with electrons orbiting in distinct energy levels.
Models evolve with new information and explain natural phenomena.
Timeline of Atomic Theory
Democritus: 400 BC - Proposed that matter can only be divided to a certain limit.
John Dalton: Early 1800s - Atoms are indivisible and form elements and compounds.
J.J. Thomson: 1897 - Introduced the Plum Pudding model showing atoms as a mix of positive substance with scattering electrons.
Ernest Rutherford: 1911 - Conducted the Gold Foil Experiment revealing that atoms consist mostly of open space with a dense nucleus.
Niels Bohr: 1913 - Proposed electrons exist in fixed energy levels around the nucleus.
Key Theorists
Democritus
Initiated atomic theory over 2400 years ago.
Argued for atoms as indivisible particles.
Dalton's Model
All elements are composed of atoms; atoms are indivisible and indestructible.
Thomson's Model
Atoms consist of negatively charged electrons in a positively charged matrix.
Discovered corpuscles (electrons) indicating that atoms contain smaller particles.
Rutherford's Experiment
Gold Foil Experiment showed the nucleus is small, dense, and positively charged, proving atoms are mostly open space.
Bohr and Modern Models
Bohr Model: Electrons have defined orbits around the nucleus.
Wave Model: Electrons do not have fixed paths; instead, they exist in a probabilistic electron cloud.
Electrons whirl around the nucleus, influenced by their energy levels.