Modern Atomic Theory

Bohr Model (1913) All materials are made up of tiny solid particles called atoms. At the center of this atom is a dense positive area consisting of protons and neutrons called the nucleus. Electrons move in definite orbits around the nucleus. These orbits or energy levels are located at certain distances from the nucleus.

Bohr’s Model nucleus Electrons

Neils Bohr

This isn’t the current model Bohr himself quickly disagreed with his own model. The problem is with the orbits of the electrons.

Wave Model (present day) based on complex math equations orbits are more complex than originally thought de Broglie stated that electrons (particles) have wave properties, and he viewed these as standing waves, like those produced when a guitar string is plucked (classical physics.) Schrodinger assumed that the electron in Hydrogen behaves as a standing wave.

Wave Model (continued) When Schrodinger’s equation is analyzed, many solutions are found. Each solution represents an atomic orbital. An atomic orbital is the most probable location for finding an electron.

What is an orbital? It is not a Bohr orbit (not moving in a circular path.) How is the electron moving? We don’t know! There is a fundamental limitation to just how precisely we can know both the position and momentum of a particle at a given time

This is kind of how we assume an electron travels

Heisenberg Uncertainty Principle The more accurately we know the particle’s position, the less accurately we can know it momentum and vice versa. We can’t know the exact motion of the electron around the nucleus. The area that an electron orbits is called an “electron cloud”

Louis de Broglie Erwin Schrodinger

Werner Heisenberg

Homework Read section 5.1, 5.4 and 5.5 Do questions on pages 175-177 1-4, 12-18