Atomic.Modern+Physics

When light passes through a gas, certain wavelengths of the light are absorbed. The result is a unique **absorption spectrum**. Two examples are shown below.
 * Prior Knowledge Questions ** (Do these BEFORE using the Gizmo.)



1. What colors of light are absorbed by hydrogen gas? Violet, blue, blueish-green, orangeish-red


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2. What colors of light are absorbed by helium gas? Deep purple, blue, lighter blue, greenish-blue, yellow, reddish-orange

In 1913, Niels Bohr proposed that the unique spectral lines created by different elements were related to the way electrons were arranged around the nucleus. The //Bohr Model: Introduction// Gizmo™ explores this connection. Open up this Gizmo now.
 * Gizmo Warm-up **

The **laser** shown in the Gizmo can emit **photons**, or particles of light, at a variety of wavelengths. The energy of a photon, measured in **electron volts** (eV), is inversely proportional to its wavelength. Photons that pass through the gas are detected by the photon detector at right.

1. With the **Energy (eV)** set to 1 eV, click **Fire**. Did the photon go straight through the gas in the tube, or was it absorbed by the gas? The photon went straight through the gas in the tube.

2. Set the **Energy (eV)** to 4 eV, and click **Fire**. What happened this time? The photon (which was that of a wavelength depicting the color blue) was absorbed by the gas.


 * ACTIVITY A: ABSORPTION SPECTRA **

Get the Gizmo ready: On the simulation pane, select lamp. Check that GAS A is selected.


 * Introduction: ** The smaller the wavelength of a photon, the greater its energy. We can see photons with wavelengths between 700 nanometers (red) and 400 nanometers (violet), corresponding to energies between 1.8 and 3.1 eV.

__ 1. Record __ : Click **Fire**. The lamp emits photons of 1 eV, 2 eV, and so on up to 20 eV. The **EL Photon Detector Display** shows the photons that pass directly through the gas. Any missing photons were absorbed by the gas before being reemitted at various angles. Which photon energies were absorbed by **Gas A**? 4 eV, 7 eV, 13 eV, 19 eV

__ 2. Observe __ : Select the **Laser** on the left and the ORBITALS tab on the right. Set the **Energy (eV)** to 4 eV. The atom model at right, called the **Bohr model**, shows the nucleus of the atom as a dark blue dot. Colored rings surrounding the nucleus represent the **orbitals** that the electron (red dot) can follow. The variable “n” represents the orbital number. Click **Fire** and watch closely. What happens? The photon is absorbed and the electron jumps to n 2. The photon is then emitted and the electron goes back to n 1.

__ 3. Analyze __ : Click **Fire** again. This time, focus on the colors of the photons that enter and exit the atom.

1. What color is the incoming 4-eV photon? Violet. 2. What happens to the electron when the photon is absorbed? The electron jumps to a higher orbital 3. What color is the emitted photon? Violet 4. What happens to the electron when the photon is emitted? The electron goes back down to the original orbital 5. If necessary, turn on **Show energy of emitted photon(s)**. What is the energy of the emitted photon? 4 eV

__ 4. Predict __ : What do you think will happen if you fire a 7-eV photon at the atom of **Gas A**? How about a 13-eV or a 19-eV photon? The electron will jump to a higher orbital than the lower energy photon corresponding with an exact orbital level.

__ 5. Gather data __ : Test your predictions with the Gizmo and fill in the table below. (The first row has been filled in for you.)


 * ** Photon energy ** || ** Effect on electron ** || ** Energy of emitted photon(s) ** ||
 * 4 eV || Electron moves up to n = 2 and then back down to n = 1. || 4 eV ||
 * 7 eV || Electron moves up to n = 3 and then back down to n = 1. || 7 eV ||
 * 13 eV || Electron moves up to n = 4 and then back down to n = 1. || 13 eV ||
 * 19 eV || Electron moves up to n = and then down to n = 3 and then down to n = 2 and then back down to n = 1. || 3 eV, 4 eV, and 12 eV ||

__ 6. Analyze __ : Find the total energy of each set of emitted photons. How does each sum relate to the energy of the absorbed photon? The total energy emitted is equal to the total energy absorbed. __ 7. Explore __ : With the **Energy (eV)** set to 19 eV, click **Fire** six times. Record the energy of the emitted photons each time. Record the results of each trial below.


 * ** Trial ** || ** Energy of emitted photons (in eV) ** || ** Trial ** || ** Energy of emitted photons (in eV) ** ||
 * 1 || 4, 15 || 4 || 6, 13 ||
 * 2 || 4, 15 || 5 || 4, 15 ||
 * 3 || 3, 4, 12 || 6 || 3, 4, 12 ||

__ 8. Analyze __ : When an electron moves from a higher orbital to a lower one, does it always follow the same path? Explain

No it doesn't. The emitted electrons are not always the same**.** An electron can jump multiple orbitals at a time but when it falls it can fall to any of the levels in between.


 * Activity B: Energy Levels **

Get the Gizmo ready by selecting the ENERGY LEVELS tab. Check that Gas A is selected.


 * Introduction: ** When an electron absorbs a photon, it gains energy, causing it to move to a higher orbit. Because each possible orbit is associated with a specific amount of energy, the orbits are known as **energy levels**. Each element has a unique set of energy levels.

__ 1. Record __ : By convention, an energy of 0 eV is assigned to the energy level that is infinitely far from the nucleus. As a result, each energy level is assigned a negative energy value. The energy levels for **Gas A** are shown on the graph. What is the energy of each level? n = 1: -20 eV, n = 2: -16 eV, n = 3: -13 eV, n = 4: -7 eV, n = 5: -1 eV

__ 2. Calculate __ : How much energy would an electron have to gain to move from n = 1 to n = 4? 13 eV __ 3. Test __ : Set the **Energy (eV)** to this level and click **Fire**. What happened? The electron jumped up to n = 4 and then back down to n = 1. __ 4. Make connections __: Recall that **Gas A** absorbs photons with the following energies: 4 eV, 7 eV, 13 eV, and 19 eV. How do these values relate to the energy level diagram? Test your ideas using the Gizmo. These are the values that allow the electron jump to energy levels 2, 3, 4, and 5 respectively. __ 6. Record __ : Each element has a unique configuration of energy levels. Select **Gas B** and record the energy of each energy level for this gas. n = 1: -19 eV, n = 2: -14 eV, n = 3: -13 eV, n = 4: -8 eV, n = 5: -2 eV

__ 7. Predict __ : Based on these energy levels, which photons do you expect **Gas B** to absorb? 5 eV, 6 eV, 11 eV, 17 eV __ 8. Test __ : Select the **Lamp** and click **Fire**. Which photons were absorbed by **Gas B**? 5 eV, 6 eV, 11 eV, 17 eV __ 9. Record __ : Select **Gas C** and click **Fire**. Which photons were absorbed by **Gas C**? 3 eV, 8 eV, 11 eV, 16 eV __ 10. Predict __ : BEFORE using the GIZMO and based on the data you collected, describe an energy levels graph for **Gas C**. (Hint: In **Gas C**, the first energy level is -18 eV.) -18 eV, -15 eV, -10 eV, -7 eV, -2 eV __ 11. Apply __ : Select the **Laser**. When you have finished, select the ENERGY LEVELS tab to check your answer. Take a screenshot of the actual graph. __ 12. Practice __ : For **Mystery A** and **Mystery B**, you are not given the actual energy level diagram. Use the **EL Photon Detector Display** to infer the energy level diagrams for each mystery element. (Hint: For each mystery gas, assume the first energy level is -20 eV.) Make a sketch on the computer or on paper and post a picture of it on your wiki.



** Complete the 5 assessment questions that follow this Gizmo. **


 * PART 2: The Bohr Model of Hydrogen **


 * Prior Knowledge Questions ** (Do these BEFORE using the next Gizmo.)

1. What happens to an electron when it absorbs a tiny packet of light called a **photon**? It moves up to a higher energy level. 2. What happens to an electron when it emits a photon? It moves down to a lower energy level.
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 * Gizmo Warm-up **

When white light is passed through hydrogen gas and separated by a prism, some wavelengths of light are absorbed by the hydrogen atoms in the gas. This causes black bars to appear in the **absorption spectrum** of hydrogen. An **emission spectrum** is created when hydrogen gas emits light.

The **Bohr model** of the atom was inspired by the spectrum produced by hydrogen gas. The link between light and atomic structure is illustrated by the //Bohr Model of Hydrogen// Gizmo. Open the Gizmo. The Gizmo shows a **laser** pointed at a container of hydrogen gas. After passing through the gas, light from the laser goes through a prism and is detected on a screen.

1. With the **Laser energy** set to 7.0 eV, click **Play**. Observe the red electron on the ORBITALS pane. Do 7.0-eV photons have any effect on the electron? No. The electron stays at energy level 1. 2. Click **Pause**. Set the **Laser energy** to 12.1 eV and click **Play**. What happens to the electron now? The electron moves up to energy level 3. 3. Under **Go to energy level**, select **1**. Notice that a photon is emitted by the electron. What is the energy of the emitted photon? 12.1 eV


 * Activity A: The Spectrum of Hydrogen **


 * Introduction: ** The shorter the wavelength of a photon, the greater its energy. We can see photons with wavelengths between 700 nanometers (red) and 400 nanometers (violet), which correspond to energies of 1.8 to 3.1 **electron volts** (eV).

1. Get the Gizmo ready by clicking Reset.

__ 2. Measure __: Set the **Laser energy** to 0.1 eV. Click **Play**, and slowly increase the energy in 0.1 eV increments so that the **Total absorption spectrum** is filled in. Stop moving the slider when the first photon is absorbed. (Hint: Be sure that //every// energy value is tried.)

3. What is the energy of the absorbed photon? 10.2 eV 4. What effect does this photon have on the electron? The photon's energy is absorbed and the electron is excited, causing it to move up an energy level. 5. The absorbed photon moves the electron to a higher **orbital**, or **energy level**. Under **Go to energy level**, click **1**. What is the energy of the emitted photon? The energy of the emitted photon equals the energy of the absorbed photon. 10.2 eV. __ 6. Measure __ : Increase the **Laser energy** by 0.1 eV, and click **Play**. Continue to raise the **Laser energy** until the next photon is absorbed.

1. What is the energy of the absorbed photon? 12.1 eV 2. On which energy level can you find the electron now? n = 3 3. Go back to energy level 1. What is the energy of the emitted photon? 12.1 eV

__ 7. Measure __ : Increase the **Laser energy** by 0.1 eV, and click **Play**. Use the Gizmo to find the energy of photons that move the electron from the first energy level up to the fourth, fifth, and sixth energy levels. (Remember to move the electron back to energy level 1 each time.)

1. What is the energy of a photon that moves the electron from energy level 1 to energy level 4? 12.4 eV 2. What is the energy of a photon that moves the electron from energy level 1 to energy level 5? 13.1 eV 3. What is the energy of a photon that moves the electron from energy level 1 to energy level 6? 13.2 eV

__ 8. Make a rule __ : How does the energy needed to move an electron to a higher energy level compare to the energy emitted when the electron moves back to the lower energy level? The energy absorbed equals the energy emitted when the level change is to and from the same level. __ 9. Interpret __ : Look at the **Total absorption spectrum**. What do the black bars in the spectrum represent? They represent the absorbed photons. __ 10. Explore __ : Move the electron to energy level 1, set the **Laser energy** to 13.3 eV, and click **Play**. What happens? The electron moved past the third energy level.

NOTE: There are several energy levels for hydrogen that are not shown in this Gizmo. The electron is in one of these energy levels.

The electron moves from energy level 6 to energy level 1 and then past the sixth energy level. The electron has been removed __ NOTE __ : The **ionization energy**, or energy required to free the electron completely, is 13.6 eV for hydrogen.
 * 1) __ Explore __ : Under **Go to energy level**, select **6** and then **1**. Set the **Laser energy** to 13.6 eV, and click **Play**. What happens now?

No. The increments of values in the spectrum move in smaller values than can be described in the gizmo.
 * 1) __ Think and discuss __ : Do you think you have completed the spectrum of hydrogen? Explain.


 * Activity B: Energy Levels **


 * Introduction: ** When an electron absorbs a photon, it gains energy. The added energy causes the electron to move to an orbit that is farther from the nucleus. Because each possible orbit is associated with a particular amount of energy, orbits are known as energy levels. By convention, an energy of 0 eV is assigned to the energy level that is infinitely far from the nucleus. (This is done so that atoms of different elements can be compared from a common starting point.) As a result of this convention, each energy level has a negative energy.


 * 1) To get the Gizmo ready, set the energy level to 6, select the ENERGY LEVELS tab, and click Reset.
 * 2) __ List __ : Look at the graph of energy levels. List the energy of each level (n = 1, 2, 3, etc.): n = 1: __-13.6 eV, n = 2: -3.4 eV__, n = 3: -1.5 eV__, n = 4:__ -.8 eV, n = 5: __-.5 eV, n = 6: -.4 eV__
 * 3) __ Predict __ : How much energy would an electron have to gain to move from energy level 2 to energy level 3?
 * 4) __ Test __ : Under **Go to energy level**, select **2**. Set the **Laser energy** to the value you think is required to move the electron up to energy level 3, and press **Play**.

1. What happens? The electron moves to the third energy level 2. What do you see on the **Total absorption spectrum**? A black line 3. What do you see on the **Visible absorption spectrum**? A black line 4. Select energy level 2. What is the energy of the emitted photon? 1.9 eV

__ 5. Make a rule __ : In general, how do you calculate the energy of a photon that is needed to move an electron between two energy levels? Find the difference between the two energy levels. __ 6. Calculate __ : Calculate the energy required to move the electron for each transition listed in the table below. Show your work for the first example only.


 * ** Transition ** || ** Energy (eV) ** || ** Transition ** || ** Energy (eV) ** ||
 * n1 to n2 || 10.2 || n2 to n6 || 3 ||
 * n1 to n3 || 12.1 || n3 to n4 || .7 ||
 * n1 to n4 || 12.8 || n3 to n5 || 1 ||
 * n1 to n5 || 13.1 || n3 to n6 || 1.1 ||
 * n1 to n6 || 13.2 || n4 to n5 || .3 ||
 * n2 to n3 || 1.9 || n4 to n6 || .4 ||
 * n2 to n4 || 2.6 || n5 to n6 || .1 ||
 * n2 to n5 || 2.9 ||||  ||


 * 1) Check your answers using the Gizmo__.__

__ 2. Interpret __ : We can see photons that are between 1.8 and 3.1 eV. Based on the table above, how many lines do you expect to appear in the visible absorption spectrum? Four __ 3. Create __ : Based on the table above, use the Gizmo to create the complete absorption spectrum of hydrogen. When the spectrum is complete, click the **COPY SCREEN** button. Paste the image into your wiki.

__ 4. Explore __ : Select the ORBITALS tab. On the SIMULATION pane, select **Current**. In this mode, an electrical current passes through the hydrogen. What is happening on the ORBITALS pane? The electron travels to a different energy level. When the photon is emitted it returns to the original level. __ 5. Compare __ : The emission of photons results in an emission spectrum. Click **COPY SCREEN** and paste this image below the image of the absorption spectrum. How does the emission spectrum of hydrogen compare to its absorption spectrum?

** Complete the 5 assessment questions that follow the Gizmo. **

What does the absorption spectrum of an element indicate about its electron configuration? It shows the photon energy required to make an electron change energy levels. How are energy levels related to absorption spectra? Each line on the absorption spectrum indicates the amount of energy required for an electron to move to a certain level. Which photon energies make up the spectrum of hydrogen? 13.6 eV, 3.4 eV, 1.5 eV, .8 eV, .5 eV, .4 eV How do energy levels relate to the spectrum of hydrogen? Each of the energy levels is represented by a line on the total emission spectrum.
 * 1) __ Conclusion __ : Answer the 4 objective questions at the beginning of this document. Be sure to provide clear, concise, detailed responses in which you provide evidence for any claims you make.

= = = ** Models of the Hydrogen Atom ** =



Atomos Solid Sphere Model Plum Pudding Model Planetary Model Definite Energy Levels (Improvement upon Planetary Model) Electron Cloud Model Democritus Dalton Thomson Rutherford Bohr Assortment of scientists (including Planck, Schrödinger, Einstein, etc.)
 * // Objectives //**
 * 1) Distinguish between several models of the hydrogen atom visually and conceptually.
 * 2) Compare and contrast the accuracy and usefulness (including the shortcomings) of various models of the hydrogen atom.
 * 3) Relate spectrometer outputs and transitions represented on energy level diagrams to observed phenomena of the hydrogen atom.
 * // Prelab Questions //**
 * 1) Recall from Chemistry, first learning about atomic models. You may look this information up in a textbook or online resource if you need to refresh your memory. Be sure to credit your source(s) appropriately.
 * 2) List the 6 models of the atom as they evolved chronologically.
 * 1) List the scientists who are credited with their discovery.
 * 1) Provide a brief description of each model, how it differs from the previous model, and any experiment done to derive the model.
 * Atom is smallest particle of matter; atom is indivisible
 * Atoms combine and form molecules
 * Positive and negative matter with atoms (protons and electrons); concept of a nucleus
 * First modern view of an atom; electrons orbit around nucleus; atom is mostly empty space
 * Electron orbital levels; definite energy levels; electron amount in each level
 * More correct than Bohr’s model according to current physics theories

// The different colored dots represent different colored light. The size and shape of the dots are not important, only the color. // // The big question mark represents a hydrogen atom. We know that it's hydrogen; it's the internal structure and the mechanisms for causing observed phenomena that we're unsure of. //
 * Procedure: **
 * Part 1: Models of the Atom **
 * 1) Open the Java applet at PhET: [|Hydrogen Atom Model Applet] . The full address is [ [] .]
 * 2) Run the default simulation experiment by pressing the "on" button of the light source (which is a red button on the ray gun). Note that:

// You should have noticed by now that what goes in the "?" is not what always comes out. We can keep track of what's emitted by setting up a spectrometer to record emitted light. This is precisely what has been done in laboratory settings. // No. In the experiment, not all of the photons were deflected when they hit the atom. In the Billiard Ball model, however, every photon going is deflected. No energy absorption/emission || Solid Atom Sphere || No charge Sphere || Billiard Ball || Only deflects a single wavelength || “Paste” of + charge with electron inside of it || Electron in center Shapeless || Plum Pudding || Mostly empty space || This clearly didn’t work || An imploded solar system || Deflects the right amount approx. and deflects discrete wavelengths || Solar system with discrete orbitals || Electron jumps levels when it absorbs the energy from a photon || Solar System || Good amount of discrete deflections || Solar system with discrete orbitals || Electrons are waves || Solar system with waves instead of electrons ||
 * 1) Check the "Show spectrometer" box to activate the spectrometer. What does the spectrometer show? What happens to the number of emitted light “counts” as more and more interactions occur?
 * 2) Select the Billiard Ball model.
 * 3) Do you think it accurately represents what's been observed in laboratory settings?
 * 1) Why or why not?
 * 1) Going in order from top to bottom, select the different models and observe interactions as predicted by each. [Note: for the deBroglie model, there are alternative views selectable from a drop down menu at the top of the applet.] For each model selected,
 * 2) Write down your impressions of how accurately the model predicts the actual behavior.
 * 3) How is the overall appearance of the model different from the other(s) just seen?
 * 4) Describe any differences in the interactions with incident light from the other models.
 * 5) How do these models compare with other commonly known models? (i.e. rigid object of the Newtonian world, solar system like appearance, orbits, etc.)
 * || Impressions || Appearance || Differences || Comparisons ||
 * Billiard Ball || Deflects too many photons
 * Plum Pudding || Does not deflect enough photons
 * Classical Solar System || It blew up || Blown up solar system
 * Bohr || Looks pretty good
 * De Broglie Radial || Looks pretty decent
 * De Broglie 3D || Same as radial but it’s 3D || Same as radial but it’s 3D || Same as radial but it’s 3D || Same as radial but it’s 3D ||
 * De Broglie Brightness || Same as radial but it’s matte || Same as radial but it’s matte || Same as radial but it’s matte || Same as radial but it’s matte ||
 * Schrödinger || Mind boggling and weird but seems accurate || Electron cloud model || Electron waves and multiple quantum numbers describing electron levels || Composite of solar system and cloud ||

Wavelength: 92 nm Quantum Numbers (n, l, m): (4, 1, 1) Energy released = Energy absorbed
 * Part 2: Quantitative Analysis **
 * 1) Run Schrodinger’s model. Turn the spectrometer on and activate the //energy level diagram//. Note the values in the bottom right corner of the experiment window.
 * 2) Look for patterns as the quantum state changes. When you see a transition occur on the energy level, press pause and record the quantum numbers of the transition and the wavelength of the photon emitted or absorbed.
 * 1) Use the data you collected to calculate the photon energy and energy released/absorbed.

a) Does something //always// happen? What role does chance or probability play in these interactions? No, most of the time the photons pass right through the atom. And sometimes, compatible values for wavelength do not affect the atom either because the electron is already at a certain energy level and therefore emits photons instead of absorbing them. Generally, a photon will affect the electron if the electron is at the ground level. Also, the photon must be of a compatible wavelength to allow the electron to successfully jump to a new energy level.  b) This model is for the hydrogen atom. How do you think things might change for more massive atoms? More massive atoms would have different value energy levels. Therefore, photons of different wavelengths would be required to make the electron jump to a new energy level. The energy levels would presumably be farther apart and would require more energy. c)What are some shortcomings of each of these models? Billiard Ball- Doesn’t show subatomic particles. Not enough empty space  Plum Pudding- No empty space. Doesn’t accurately show subatomic particles/nucleus  Classical Solar System- Atom would blow up (fairly obvious). No discrete energy levels  Bohr- Doesn’t have sub-orbitals.  De Broglie- This seems pretty decent for all intents and purposes.  Schrödinger- Also seems pretty decent.
 * 1) After you have collected the data, answer the following questions:

For questions involving the comparison of spectrometer outputs, the simulation should be set to the “fast” setting to save time (i.e. produce more comparable results in less time).
 * // Follow-Up Questions //**

“Everything should be made as simple as possible, but not simpler.” a) What does he mean by this? Reflect back on what you’ve learned about models of the hydrogen atom in your science classes, how is this quote relevant? In order to produce accurate results, one must include all of the necessary components. Any less would not produce accurate results. Any more would produce superfluity.  b) Imagine you are a physics teacher preparing for class for your students on the hydrogen atom. Is this quote still relevant? Explain your reasoning. Yes. If the students come into the class knowing next to nothing about atomic structure, a good idea would not be to overload them with data that, without prior knowledge, is basically useless. Introduce the students to the atomic structure one step at a time so that they will understand the structure and why things occur.
 * 1) Following is a quote from Albert Einstein:

a) Run Schrodinger’s model. Select the monochromatic checkbox. Set the slider to 103nm. Interactions will occur until eventually red light is emitted — then the interactions cease. Why is this? Explain your reasoning. [Hint: have the energy level diagram open and running while you run the simulation for this question.] The photons are only of a value that allows the electron to jump from n = 3 and them back to n = 1. However, the atom may emit a photon of a wavelength corresponding to the color red from n = 3. This brings the electron down to n = 2, and from there, there is no way for the electron to make its way back down to n = 1. The electron must be excited up to n = 3 before it can go back down and continue moving. This has to do with the qualities of quantum numbers detailed with the Schrödinger model of the atom (specifically the l quantum numbers).  b) Does the same thing happen with the Bohr and deBroglie models? What is the difference? This doesn’t happen in the Bohr and de Broglie models. They do not include the quantum letter l. c) Now set the slider to 122nm. Have the energy level diagram open and running while you run the simulation for this question. Interactions will occur indefinitely, but only for transitions between //n// = 1 and //n// = 2. Why is this? What fundamental property of modern physics accounts for this? List all of the possible quantum states of a hydrogen atom for these settings. (If you only list what you see in the bottom right corner of the experiment window you’ll miss one!).  This has to do with the law of conservation of energy I think. There is not enough energy supplied by the photon to allow the electron to jump up to any energy level greater than n = 2. The possible quantum states are as follows (in the format n,l,m: (1,0,0) (2,1,-1)  (2,1,0)  (2,1,1)
 * 1) You will need to revisit the applet to answer this question.


 * 1) List all the possible quantum states of a hydrogen atom that have energy //E// = -3.40eV. Explain why this list of quantum states is similar but not exactly the same as your answer to question 3 above.


 * 1) While working on a physics problem, a friend of yours correctly determines //En// for //n// = 1 to be -13.60eV. He then uses //E// = //hf// and figures that light of 365nm should be absorbed/emitted by a hydrogen atom. Why is this incorrect? In other words, where did your friend go wrong?