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Atomic Emission Spectra
M.Ed., Columbia Teachers College
Kendal founded an academic coaching company in Washington D.C. and teaches in local area schools. In her spare time she loves to explore new places.
Atomic emission spectra are unique spectra of light emitted by an element when electricity is run through it or when it is viewed through a prism. Because they are unique, they can act as an element s fingerprint. An emissions spectrum looks like a set of colored lines on a black background as opposed to an absorption spectrum which looks like black lines on a colored background. The colors are visible portions of the electromagnetic spectrum.
Alright so we're going to talk about atomic emission spectra. It's a set of frequencies of the electromagnetic spectrum emitted by excited elements of an atom. Okay so first question is electromagnetic spectrum; let's take a look at that. Alright so here is the overall general view of the electromagnetic spectrum going from high energy wave the gamma rays to very large energy waves the radio wave. In the middle we have visible light and we're going to focus on visible light just for next couple of seconds. Alright so we know that when you take white light put it to a prism it breaks up into the rainbow the full visible spectrum. So what happens when you have light emitted from different elements than when you burn them or when you actually light something that's actually not white light when you break kit up with a prism what that actually looks like. So let's actually look at the video that shows this kind of information.
A very dramatic version of the flame test demonstration here. First, we have alcohol burning blue. Then we have some barium chloride, with barium ions burning a dirty yellow color. Then we have boron being green, strontium giving us the crimson red color. Next, is calcium giving us the orange. Not showing up very well here in the next one, but the red tints inside of that orange, there's some impurities there that is lithium. Next, we have sodium giving us a characteristic yellow flame. Then we have copper with its green color. And finally potassium with the purple, or lilac shade.
Alright so if you took a prism to those actual the frame tests from those elements being burned or those compounds being burned. Instead of seeing the whole visible region like you do up here you would see something broken up. So if you took a lithium light and broke it up you would see this just these bands within an electromagnetic spectrum and notice each element has its unique spectrum that it's going to emit. So this actually are called finger prints of each element, and we can actually determine taking a light and putting a prism up to it or what we also call diffraction grading up to the light we can actually break it up and to tell what element is actually being excited or put energy in.
We take hydrogen, which is as simple as atom and we're going to take, this is the hydrogen and the lamp it is inside of. This hydrogen and lamp we have a gas of hydrogen and obviously electricity is being put into it. So the electrons are going to be excited and we'll talk about what excited means in just a second. And if we put a prism or a diffraction grading up to this light we're going to get a unique spectrum with these 5 bands of light. One red, one teal color and a few purple and blue.
Alright so what exactly is happening and why is this happening? Okay so we go over here ground state element in a ground state picture of hydrogen the electron is in it's lowest orbital in this case n equals 1, and if you pump energy into it, this electron is going to get what we call "excited" and it's going to go up to higher energy levels as you can see over here. so we're going to put energy into it whether it be like through electricity or through fire or through whatever type of energy that you want to put into it, that electron is going to bounce up. Okay so this electron is going to bounce up to higher energy levels even though those energy levels are not necessarily occupied they are present in every single atom. So it's going to bounce up and we call this the excited state, we have excited now the atom. The atom then is going to release the energy so it's getting up there it's getting excite then energy is going to be released and it's going to go back down to a lower energy state. Okay if the energy, if the electron falls down to n equals let's go down to n equals 1, it's going to fall down to the lowest energy state back to it's ground state depending on it's going to emit bands of energy depending on how much energy is released at that period. So if it goes down it's going to release UV rays, we can't see those, we're going to call that series or Lymen series.
It's going to emit like certain energies of UV rays. If it goes to n equals 2 goes to the second energy level not quite get down to the ground state yet but almost there. It's going to release the visible region which is what we saw in the slide. That we kind of call that the Balmer series which we have like 5 I think bands of light that we saw. The last one is going to go down, if it goes down to n equals 3, that's going to emit ir rays and infrared rays and we're going to call that the Paschen Series. So what is this used for, why is this helpful? Well basically you can take all this information and get the spectrum and each spectrum is unique for each element. So then you can figure out for example fireworks because they give off the green and blues and pinks and beautiful things and what elements are going to release those colors in the air. You can use this information, also if you were to look in like a telescope and in the out of space and you have, collect light or from a certain region usually break up that light determine what elements are out there. So that's pretty much atomic emission spectra.
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