Neils Bohr 1922

Neils Bohr, like Rutherford, worked for JJ Thompson at the University of Cambridge.

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Here they were introduced and under Rutherford’s guidance, Bohr (a physicist) began studying the properties of atoms in 1912, and in 1913 Bohr proposed his revolutionary theory of the way electron’s orbit the nucleus.

His theory in a nut shell is:

electrons “jump” between energy levels or orbits in a quantum fashion, that is, without ever existing in an intermediate or in-between state.

Isn’t it fascinating that these three minds who contributed greatly to the same field of study where so intimately related!!

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Bohr realized that Rutherford’s atomic model, with the electrons orbiting the nucleus, was not quiet right because by the rules of classical physics, it should be very unstable

1. The orbiting electrons should give off energy and eventually spiral into the nucleus

2. The electron’s could be knocked out of position if a charged particle were to pass by

So classical Physics wasn’t working to describe the motion of electron’s around the nucleus, and Bohr turned to Plank’s quantum theory to explain the atom’s stability

Bohr found that the ratio of energy in an orbiting electron to the frequency with which they orbit the nucleus was equal to Plank’s Constant, leading Bohr to conclude that electron’s jump between energy levels in a quantum fashion

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Ok, so what does this mean.

Bohr’s model like Rutherford’s treats the electron’s as if they are orbiting around the nucleus, but the orbits are not confined to a plane like they are in our solar system.  Bohr’s model is similar to Rutherford’s model, but is a quantum physical interpretation of it.

The Bohr Model

1.Electrons in atoms are in orbits of different energy around the nucleus

2. These different orbits make the different energy levels or energy shells

( represented by the rings above)

3.The further an electron is from the nucleus the more energy it has

4. The energy of an electron is quantized meaning they only exist in these energy levels and nowhere in between.

(The electrons will only exist along the rings of the above picture, and not in the white space)

(Look Below This is why a quantum of energy is required to move between these energy levels)

5. The energy level an electron normally occupies is its ground state, but electron’s can become excited by absorbing energy and move to a higher less stable energy level known as its excited state.

6. After being excited the electron can return to its ground state by releasing energy.

*keep in mind there is a difference between energy orbits, and molecular orbitals.

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Bohr found that electron’s can move into a higher energy level once they receive enough energy.

This small specific amount of energy required for electrons to move between energy levels is known as a

quantum of energy.

Electron’s gain and release energy by absorbing and giving off light also known as photons.

The energy of the photon absorbed or emitted when the electron moves between energy levels is equal to difference in energy between the energy shells.

The Quantum Model has replaced the Bohr Model; however, the Bohr model is often taught in general chemistry in order to provide a more simple model to teach with.

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The Bohr Model takes into account the different energy levels, and the amount of electrons contained within them, but fails to consider the molecular orbitals contained within the different energy shells.

Each orbit or energy level described by the Bohr Model corresponds to the rows on the periodic table. image_thumb69

Each energy shell can contain a certain number of electron’s,

The quantum model which has replaced the Bohr model

takes into account the wave properties of electron’s

(Wave Particle Duality)

Atom_model

which creates some mathematical uncertainty as to where the electron’s are specifically located.

(Heisenberg Uncertainty Principle)

This has led to the molecular orbitals which are characteristic regions of space where electron’s are most likely to be.

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Below are Video Descriptions of this complicated subject matter.

http://www.screencast.com/t/bDBNbDkjn

http://www.screencast.com/t/ryM6WrrLjr

http://www.screencast.com/t/PjVx6c3H

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