Energy Bands and Molecular Orbitals

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Discussion Overview

The discussion centers around the relationship between molecular orbitals (MO) and energy bands, particularly in the context of conductivity in different materials such as potassium (K), silicon (Si), and sodium (Na). Participants explore how the characteristics of these materials relate to their electronic structures and conduction properties.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • A participant expresses confusion about how energy bands form from molecular orbitals as the number of atoms increases in a crystal structure.
  • It is noted that potassium has a fully filled σ state and an empty σ* state yet behaves as a conductor, while silicon has partially filled ∏px and ∏py states but does not behave as expected for a good conductor.
  • Another participant questions the comparison between diagrams for diatomic molecules and band structures for infinitely large crystals, prompting a discussion on their relevance.
  • A suggestion is made to understand Bloch's theorem and to perform model calculations for one-dimensional systems to gain clarity on the topic.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the relationship between molecular orbitals and energy bands, and there are competing views regarding the conductivity of different materials based on their electronic structures.

Contextual Notes

The discussion highlights potential limitations in understanding the comparison between molecular orbital diagrams and band structures, as well as the assumptions underlying the conductivity behavior of different materials.

ABhattacharya
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Hello, a newbie here. I need to understand the relationship between MO and Energy Bands.

Although i have searched and researched about this topic in Google, but i am yet to understand this part clearly.

It is said that Energy Bands occur as the number of MO increase due to the various atoms that are interlinked in a crystal structure.

But i can't help but wonder.
While K has its σ state fully filled and its σ* state empty, and yet behaves as a conductor
But Si has ∏px and ∏py states partially filled which means when bands form, Si should have some bands which are partially filled and hence should be good conductors while Na should behave more of a semiconductor way... but it is just the opposite. Why?
 

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The diagram you show seems to be for diatomic molecules while the band structure refers to infinitely large crystals. Why do you think the two are comparable?
 
DrDu said:
The diagram you show seems to be for diatomic molecules while the band structure refers to infinitely large crystals. Why do you think the two are comparable?

Then what should i do to get a clearer picture of the MO and Energy Band conduction??
 

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