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.