Energy bands in solids

Discussion in 'Homework Help' started by Legend killer, Dec 16, 2013.

  1. Legend killer

    Thread Starter New Member

    Jan 24, 2010
    10
    1
    Hello everyone,
    I am trying to learn about the energy bands which forms when atoms interact with each other. However I am unable to actually visualize the whole picture. As per my understanding I have created a diagram which I think might be correct way of visualizing the whole picture. Can anyone please tell me whether I am correct or wrong. I have attached the image with this post
     
  2. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    It's very hard to tell if you are on the right lines or not from your diagram alone without any explanation of your thinking.

    So I will make the following comments.

    I don't know what the curved blue lines with the electrons are meant to represent?

    You need to be aware that there is only one electron at any energy level per atom.
    (Or two per level if you count the Pauli pairing)

    It is only the bonding or valence electrons that take part in fromation of molecular orbitals that lead to the energy bands.
    The main core of electrons remain unaffected.
    Note it is often said that these bonding electrons are the outmost electrons but that is not always the case.

    With only two atoms participating you only get a well defined molecular orbital. When you get a vast array of atoms participating these molecular obitals smear out to form the energy bands.

    Is your ultimate goal to use energy bands to understand insulators, conductors and semiconductors and perhaps tunneling?
     
    Last edited: Dec 16, 2013
  3. amilton542

    Active Member

    Nov 13, 2010
    494
    64
    I'm at odds just how two atoms could interact when, by way of your diagram, they're an infinite distance d apart.

    Being well versed with the periodic table and how solids, such as alloys, are formed is rudimentary ground that needs to be covered.

    By the way, the energy levels associated with the orbits of electrons is quantem mechanics. This stuff is not easy. Some engineers will bite, others will not.
     
  4. Legend killer

    Thread Starter New Member

    Jan 24, 2010
    10
    1
    Hello studiot and amilton542
    Thanks for your replies
    In the diagram( two atoms shown on top), i was indicating that the electrons in atoms have discrete energy levels when they are isolated from each other. The blue lines indicates orbits which i have not drawn as complete circles and i have also indicated y-axis as energy which indicates that energy of electrons increases as distance from nucleus increases. Next (atoms shown in bottom), i have drawn four lines instead of one because now there will not be single discrete energy level, instead there will be four closely spaced energy levels for the four electrons (as per my understanding).
    Am i correct or wrong in my understanding?
     
  5. Papabravo

    Expert

    Feb 24, 2006
    10,138
    1,789
    Atoms in isolation have plenty of discrete energy levels without regard to any other atoms. An atom can absorb a photon and be boosted to a higher level by absorbing the photon energy. When the electron drops back to a lower state it emits a photon with a well defined wavelength based on the amount of energy given up.

    What happens when atoms are in proximity is that the most energetic electrons are in the so-called valence band. It is the electrons in this valance band that have the most influence on the chemical and electrical properties. There are also electrons that are far enough away from any nucleus to be considered essentially "free" electrons or "conduction" electrons. In semiconductors there is an energy gap (aka "band gap") between the valence electrons and the conduction electrons.

    In your picture there is a suggestion that proximity creates new discrete energy levels where none existed before. This is not the case. Any given electron with some non-zero probability can have any combination of quantum numbers that are available. For example, a Hydrogen atom has a single 1s electron. The 1s refers to the lowest energy level an electron of a hydrogen atom can have. If it absorbs a photon, raising its energy level, it might become 4p electron for a short time and then return to the 1s state after one or more quantum jumps.

    These links might help
    http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch6/quantum.html
    http://en.wikipedia.org/wiki/Band_gap
    http://en.wikipedia.org/wiki/Pauli_exclusion_principle
     
    Last edited: Dec 17, 2013
Loading...