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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