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Question on Spectra and Energy- LC Chemistry

  • 30-11-2014 4:52pm
    #1
    Corkgirl18
    Closed Accounts Posts: 894 ✭✭✭


    This might be a stupid question but I am very confused.
    I'm studying Bohr's theory and spectra at the moment.
    Each element has its own unique emission line spectrum - fair enough.

    But if you increase the energy supplied to an element why does the colour stay the same? If increase in energy shouldn't the wavelength decrease and the frequency increase which would change the colour?
    Why is the wavelength fixed?
    Thanks!


Comments

  • #2
    Ciaran
    Registered Users, Registered Users 2 Posts: 971 ✭✭✭Ciaran


    The idea is that electrons can only have certain specific energies. The emission lines come from electrons moving from one energy level to another so only light with wavelengths corresponding to the differences between one level and another can be emitted. If you supply more energy, you'll get more light emitted at these same wavelengths but not at new ones. What would happen is that lots more electrons would get some energy and jump up and then fall down through the energy levels.

    It's a while since I studied this so I may have some of the details wrong but that's how I understand it.


  • #3
    Labarbapostiza
    Banned (with Prison Access) Posts: 963 ✭✭✭Labarbapostiza


    Corkgirl18 wrote: »
    But if you increase the energy supplied to an element why does the colour stay the same? If increase in energy shouldn't the wavelength decrease and the frequency increase which would change the colour?
    Why is the wavelength fixed?
    Thanks!

    You're confusing two things, that often get confused.

    There's two different kinds of spectra. Line spectra and continuous spectra. Line spectra is caused by electrons jumping from one energy level to another in an atom. It's limited to specific frequencies. It's just one set of colours, depending on the atom. it doesn't change colour when you add more energy.

    Continuous spectra is something different, it's also called black body radiation. When the atoms heat up in anything, they bash against each other, this releases photons, but you get a broad spectra - that's lots of different colours. If you heat metal, first you can't see the infra-red, then it glows red, keep going it will glow white, and then blue if you can keep heating it.


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