Questions about atomic theory

In summary,1. Some textbooks published in 2007 still use the Bohr atomic theory to explain electron movement.2. The satellite valley is a term used to describe the energy states that electrons take up in an atom.3. Electrons do not move freely in an atom, but have specific patterns of motion that are connected to specific, discrete, energy states.4. The electron mobility is greater than the hole mobility because the hole cannot tunnel.5. The paragraph in question is confusing, and the screenshot provides an explanation.
  • #1
prescott2006
25
0
1. Isn't it the Bohr atomic theory is proven incorrect, why some textbook even that publish in 2007 still use it to explain about electron movement? Isn't it should be using SPDF theory?
2. What is meant by satellite valley?
3. How is electron move in atom if not circulate in an orbital?
4. Why is electron mobility greater than hole?
5. I am reading a semiconductor book and I found a sentence confused me, the screenshot is attached below.
Thanks for helping.
 

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  • #2
1) Well, they're not usually purporting to give a true explanation of electronic motion, but to illustrate the basic principle that electrons in an atom cannot move freely, but have specific patterns of motion connected to specific, discrete, energy states. (Also perhaps that these states are related to angular momentum, although the specific angular momenta of the Bohr model are wrong). That's the only valid lesson that can be drawn from it, apart from its historical significance. The alternative here is simply quantum theory. "SPDF" is actually slightly misleading, since those are spectorscopic designations originally, which the more sophisticated Bohr-Sommerfeld models did take into account by introducing more quantum numbers. But none of that was really adequately justified theoretically. (Which is basically what everyone was busy trying to do up until Schrödinger, 1926)

2, 4) I think I know, but I'm not a solid-state guy so I'll pass on these, since there are folks posting here who I'm certain will give better answers than I could.

3) I'd have to say 'quantum-mechanically'. The electrons have no definite location, and correspondingly, no definite trajectory. They tunnel, and have no problems moving from one location to another without passing intermediate points (e.g. consider a p-orbital; it has a nodal plane perpendicular to the two lobes, where the probability of finding the electron is exactly zero.) It's tempting to think of them as not moving, since their probability density is static. But they do move; they have kinetic energy. They exhibit many-body effects and relativistic effects due to motion, etc. But fundamentally this boils down to the unresolved issue of how to interpret QM.

5) That's basically a way of looking at it that comes from basic chemistry, or for a somewhat more advanced theoretical justification, valence-bond theory. Basically you can look at the chemical bond in terms of two idealized extremes: A covalent bond, where the two electrons that form the bond are shared exactly equally between the two atoms, and an ionic bond, where one electron from the Gallium atom is entirely on the Arsenic atom.

In chemistry they look at that as 'resonance', you have two resonance forms:
Ga-As (covalent) <--> Ga+-As- (ionic)

In the latter case you have more electrons on the arsenic. In reality, bonds between two different nuclei are never purely covalent or purely ionic. So what they're saying here is that the covalent form dominates, but there's a slight ionic contribution, and conclude that there's a 'little bit' more of the bonding electrons on the arsenic. I recently got http://i.imgur.com/tow7V.jpg" to a cute explanation from an organic chem textbook. As it explains, these two resonance forms don't actually exist, they're just a theoretical way of looking at it. A more rigorous justification for that way of looking at it is valence-bond theory, in which the covalent and ionic forms can be viewed as two different quantum states with two different wave functions, and the real ground state is a superposition of the two. In this case, a superposition where the covalent contribution is largest.

So don't read too much into it, it's really just the result of a particular theoretical way of looking at it. Physically it doesn't amount to more than the observation that arsenic is slightly more http://www.thecatalyst.org/electabl.html" [Broken] than gallium.
 
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  • #3
Thanks for the explanations. And the rhinoceros explanation is really cute.:tongue: Now left question 2 and 4. But maybe you can try to explain as well, I think you really understand it.:tongue: Also, I am having problem in understand the quantum well, wire and dot. I Google and read them but I don't think I fully understand it. Can you please explain in a simpler way maybe? And another thing is I read from somewhere that the colorful liquid composed by quantum dot does not precipitate, i.e they remain the color as it is no matter how long it is been put there. Can you explain this phenomena?
 

1. What is atomic theory?

Atomic theory is a scientific explanation that describes the nature of matter at the atomic level. It states that all matter is made up of tiny particles called atoms, which are the building blocks of all substances.

2. Who proposed the concept of atomic theory?

The concept of atomic theory was proposed by a Greek philosopher named Democritus in the 5th century BC. However, it was not accepted by the scientific community until the 19th century when scientists such as John Dalton, J.J. Thomson, and Ernest Rutherford contributed to its development.

3. What are the main principles of atomic theory?

The main principles of atomic theory include the following:- All matter is made up of tiny particles called atoms.- Atoms of the same element are identical in their physical and chemical properties.- Atoms of different elements have different properties.- Atoms can combine with each other to form compounds.- Chemical reactions involve the rearrangement of atoms, but the atoms themselves remain unchanged.

4. How has atomic theory evolved over time?

Atomic theory has evolved significantly over time as new scientific discoveries have been made. Initially, it was believed that atoms were indivisible, but later experiments showed that they were made up of even smaller particles such as protons, neutrons, and electrons. The discovery of isotopes, subatomic particles, and quantum mechanics have also led to advancements in atomic theory.

5. Why is atomic theory important?

Atomic theory is important because it helps us understand the fundamental nature of matter and how it behaves. It has allowed scientists to make predictions, develop new technologies, and improve our understanding of the world around us. Without atomic theory, many scientific advancements, such as the development of modern medicine and electronics, would not have been possible.

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