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Atomic emission spectra
CHEMISTRY - Secondary 2
In This part we will study:
Atomic emission spectra
 The principle of modern atomic theory (modification of Bohr's model)
The modern atomic theory is based on some essential modifications of Bohr's model.
The most important modifications are the following:
A- The dual nature of electron.
B- The Heisenberg uncertainty principle.
C- The wave-mechanical theory of the atom.
A- The dual nature of electron.
All the previously mentioned theories considered the electron just as a minute negatively charged particle. However, all experimental data showed that the electron has a dual nature, as it is a material particle which also has wave properties.

The dual nature of electron: The electron is a material particle which has wave properties.
B- The Heisenberg uncertainty principle.
Bohr's theory postulated that it is possible to determine both of the location and velocity of the electron precisely at the same time, but by applying the principles of quantum mechanics, Heisenberg concluded that "the determination of both the velocity and position of an electron at the same time is practically impossible.
So, to speak in terms of "probability" seems to be more precise".
This is because the electron wave motion doesn't have a certain location.

Heisenberg uncertainty principle: The determination of both the velocity and position of an electron at the same time is practically impossible and this is subjected to the laws of probability.
C- The wave-mechanical theory of the atom.
The Austrian scientist Schrodinger (1926) applied the idea of Planck, Einstein, De Broglie and Heisenberg and could:
• Establish the wave-mechanical theory of the atom.
• Derive a wave equation that could describe the electron wave motion in the atom.

On solving Schrodinger's equation, it is possible to:
 Determine the allowed energy levels.
 Define the regions of space around the nucleus, where it is most probable to find the electron in each energy level.

• The wave-mechanical theory changed our concept about the movement of electron, where instead of speaking about the fixed circular orbits as being completely forbidden for electrons, the concept of "the electron cloud" (region A ) is used to express the region of space around the nucleus.

Electron cloud: It is the region of space around the nucleus, in which the electron probably exists in all directions and distances (dimensions) (region A).
Orbital: It is the region within the electron cloud which have high probability of finding the electron.

Best wishes to you
Mr.Ahmed Elbasha

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