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Niels BohrBased his studies on
HydrogenProposed energy
levelsPlanetary model of
the AtomWe still use this today
to estimate place of electron
Niels Bohr Niels Bohr (1885-1962)
(Nobel Prize, 1922)
electron
nucleus
orbit
Bohr’s Model
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.
nucleus
first
second
third
fourth
fifth
Ene
rgy
Lowest Energy State is called the Ground State (n=1)
Ground State is closest to the nucleus
When an atom gains energy, electrons are raised to an excited state
Electrons move in certain allowed orbitals
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
Bohr to quanta
Quantization of Energy was started by
Max PlanckPlanck’s hypothesis:
Matter can only gain or lose energy in small specific amounts called a quantum.
(1858-1947)(1858-1947)
Louis de BroglieProposed 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 PrincipleSaid 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
Atoms have:
• A nucleus• small, heavy part of the atom
•An electron cloud• large, lightweight part of the atom
Nucleus Electron Cloud
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