1. Electrons and Light
How does the arrangement of electrons in the atom determine the color of light that it emits?

2. Electrons and Light
The color of light emitted from an atom is based on the energy associated with electrons.
Light energy travels in waves, packaged into bundles called photons.
The amount of energy is determined by the frequency and wavelength of the wave.
Frequency- number of cycles of each wave per second
Wavelength- distance between peaks or troughs
The shorter the wavelength, the higher the frequency and energy and visa versa. (inverse relationship)
First off- lets just get a little bit of a review- perhaps some stuff you already know about light and energy. Read slide.

3. Inverse Relationship Between Frequency and Wavelength
Lets look a little more closely at this inverse relationship. Notice here that in the first axis wavelength is measured in meters. Radio waves, have a wavelength of 10 3 or 1000 meters. That’s a long wavelength. The picture of the wave in the box shows this long wavelength. Moving right on the axis, the wavelength shortens, gamma rays have a wave length of This wavelength is very small. In the axis below the wave box, frequency is shown. Recall that frequency is the number of cycles of the wave per second. The frequency of a long wavelength is small compared to the frequency of a short wavelength. Think of it as if you’re covering the same distance, at the same speed, but one person is taking long monster steps and another person is taking tiny baby steps. To cover the same distance in the same amount of time, the person taking baby steps(short wavelength) have to step faster (higher frequency). Also notice how wavelength and frequency are related to color. Red light has a longer wavelength, but a lower frequency than violet light, which has the shortest wavelength and highest frequency. (Inverse relationship)

4. The Electromagnetic Spectrum
Before I go on about this slide, notice that the spectrum is flip flopped. The red end is on the right instead of the left, like in the last slide. See…. It doesn’t matter which way the spectrum is presented. The longer wavelength is always going to go with the red end and the shorter wavelength is always going to go with the violet . When we’re talking about the color of light, we’re only talking about a small part of the electromagnetic spectrum. You can see how gamma rays have a much smaller wavelength that the purple part of the visible light spectrum. This also indicates that gamma rays have the highest frequency and energy of all other types of energy on the spectrum.
Visible light is just a small part of the spectrum
The wavelength determine the color!
The purple end of the spectrum has a shorter wavelength, but higher energy!

5. The Bohr Model Matters
Alright, so moving on to how the light gets produced… Remember that the Bohr Model of the atom is actually not the most recent model . However, it is very useful in helping us understand how light is produced from the electrons in the atom. Notice in the model, that nucleus in the center and rings or orbits around the nucleus that are called energy levels. This is where the electrons “live” in the atom. Each energy level is defined by a number, starting with 1 closest to the nucleus and going out from there. See, n=1, n=2 and so on. Each energy level is defined by a specific allowable amount of energy. This means that when an electron is in a certain energy level, it must have only the certain amount of energy that matches the leve.
Energy levels are defined as n=1, n=2, n=3, and so on
Each energy level is defined by a specific allowable amount of energy.

6. The Bohr Model Matters
Energy levels are different and unique for each element.
The emission spectra of various elements showed us this.
Energy levels are different and unique for each element. The spectral lines in the emission spectra of an element shows the energy levels that are possible for each atom of that element. So, you can think of it as an orbit from the Bohr model matches each spectral line. For instance, since hydrogen only has 1 electron, it will have fewer spectral lines than an element that has many electrons. It’s a little more complicated than that, but it works for now.

7. So how does light come from an atom?
An electron at its ground state absorbs energy causing it to jump to a higher energy level.
The electron is now at the excited state.
The electron immediately releases this energy in the form of a photon, and returns to its ground state.
So, how does it happen? First look at the white cicle, which is an electron, in the n=2 orbit. At this point, the electron is in the ground state, its home. In order for an atom to release energy as light, it first has to absorb the right amount of energy. This picture shows that this electron absorbs energy that would match a wavelength to produce red light (because the squiggle arrow is red). When it absorbs the energy, it jumps up to a higher energy level. When it gets to this higher energy level, it is in an excited state. It instantly returns to the ground state, and in the process of returning to the ground state, releases the energy that it had absorbed. Therefore the light it releases is red. Now look at the electron in the n=1 energy level. This shows that a photon of purple light was emitted when it returned to its ground state. This tells us that it had to have absorbed this same amount of energy to make the leap from n=1 to n=3. Here’s a thinker question- why do you think the light emitted from the electron that falls from n=3 to n=2 would be red, while the one that falls from n=3 to n=1 be purple? An electron that is closer to the nucleus would require more energy to push to the n=3. Therefore, it would also release this higher level of energy in the form of purple light. The electron in the n=2 level is held less tightly to the nucleus, so less energy is required for it to jump to n=3. Therfore the energy is releases matches a wavelength this is associated with red light.