Niels Bohr Based his studies on Hydrogen Proposed energy levels Planetary model of the Atom We still use this today to estimate place of electron Niels Bohr (1885-1962) (Nobel Prize, 1922)

Bohr’s Model nucleus electron orbit sample-millikan1.mov

Bohr Analogy An Onion If you cut an onion in half you’ll see rings. Bohr’s model has “rings” called energy levels in which the electrons are located outside of the nucleus.

Bohr's Energy Levels When an atom gains energy, electrons are raised to an excited state fifth fourth Electrons move in certain allowed orbitals third second Energy Lowest Energy State is called the Ground State (n=1) first nucleus Ground State is closest to the nucleus

Bohr to quanta Bohr’s theory was a great accomplishment and radically changed our view of matter. But problems existed with Bohr theory — The theory only successful for the H atom. So, we go on to Quantum Mechanical Model of the Atom was developed

Quantization of Energy was started by Max Planck Planck’s hypothesis: Matter can only gain or lose energy in small specific amounts called a quantum. (1858-1947)

Louis de Broglie Proposed the wave particle duality of nature Wave Particle duality of nature says Waves can act like particles or waves Compared electron orbitals to waves Related Planck’s quantum idea to electron orbitals to state that orbitals must be in WHOLE numbers. 1892-1987

Werner Heisenberg Proposed the Uncertainty Principle Said it is impossible to know both the exact position and velocity of an electron at the same time Make a prediction but not for sure Einstein did not like it. He said “God Doesn’t Play Dice”

Erwin Schrodinger Used de Broglie and Planck’s work to propose a new model of the atom, in which electrons are treated as waves Described three dimension area around nucleus called the atomic orbital to describe the probability of the electrons’ location Electron cloud model of an atom 1887-1961

The Modern Atom Atoms have: A nucleus small, heavy part of the atom An electron cloud large, lightweight part of the atom Nucleus Electron Cloud

Don’t forget tonight’s homework: Update the Scientist Timeline