PhET/C3/Models-of-the-Hydrogen-Atom/English-timed
From Script | Spoken-Tutorial
Time | Narration |
00:01 | Welcome to the spoken tutorial on Models of the hydrogen atom. |
00:07 | In this tutorial we will, Demonstrate Models of the Hydrogen Atom, PhET simulation. |
00:16 | Here I am using-Ubuntu Linux OS v 14.04 |
00:24 | Java v 1.7.0 |
00:29 | To follow this tutorial, Learner should be familiar with topics in high school science. |
00:37 | Using this simulation we will, Visualize different models of the hydrogen atom. |
00:44 | Explain the experimental predictions of each model. |
00:49 | Discuss limitations of each model. |
00:53 | Explain the energy level diagram. |
00:56 | Determine the orbital shape and orientation from n, l and m values. |
01:03 | Let us start the demonstration. |
01:06 | Use the given link to download the simulation. |
01:11 | I have already downloaded Models of the Hydrogen Atom simulation to my Downloads folder. |
01:18 | To run the simulation, open the terminal. |
01:22 | At the prompt type cd space Downloads and press Enter. |
01:29 | Then type, java space hyphen jar space hydrogen hyphen atom_en.jar and press Enter. |
01:41 | Models of the Hydrogen Atom simulation opens. |
01:45 | Top-left corner of the screen has a menu bar with menu items File and Help. |
01:52 | Below the menu bar, there is a grey button with two options, Experiment and Prediction. |
02:01 | By default Experiment mode opens. |
02:05 | On the screen, we see an experimental setup with a light gun to emit beam of photons. |
02:13 | There is also a Box of Hydrogen. |
02:16 | This box is filled with hydrogen atoms. |
02:20 | The zoom-in box represents a single hydrogen atom. |
02:25 | A message appears. |
02:28 | It prompts you to click on the red button to turn on the light beam. |
02:33 | The light gun has two light controls, White and Monochromatic. |
02:41 | By default White light is selected. |
02:45 | Click on Prediction option on the grey button. |
02:49 | Atomic Model panel opens on the left-side of the screen. |
02:54 | It has a list of Classical and Quantum Atomic Models. |
02:59 | Here we can check how the prediction of a model matches the experimental results. |
03:06 | Legend box on the right-side of the screen has a list of sub-atomic particles. |
03:13 | At the bottom of the screen we have, Slider to control speed of animation Play/Pause and Step buttons. |
03:25 | The first model of atom proposed, is the Billiard Ball model. |
03:30 | By default Billiard Ball is selected from the list. |
03:35 | Billiard Ball Model |
03:38 | Billiard Ball model is also called as Dalton's atomic model. |
03:44 | It was proposed by John Dalton. |
03:48 | According to this model, individual atom is visualized as solid, hard spheres, like billiard balls. |
03:58 | Click on the red button of the light gun. |
04:02 | Select White light. |
04:05 | A beam of photons having different wave lengths pass through box of hydrogen. |
04:11 | Observe that, All photons in the path of hydrogen atoms are deflected. |
04:17 | Limitations of Billiard Ball model. |
04:21 | Here are the limitations of Billiard Ball model. |
04:27 | Back to the simulation. |
04:30 | Turn off the light beam. |
04:33 | Click on Plum Pudding from the Atomic Model list. |
04:37 | This model was proposed by J. J. Thomson in 1898. |
04:43 | The positive charge is uniformly distributed and electrons are embedded into it. |
04:50 | The brown mass is the positive charge. |
04:53 | Blue color particle in the middle is the electron. |
04:57 | Click on Show spectrometer check-box. |
05:01 | Turn on the light beam. |
05:04 | Select White light. |
05:07 | When photons strikes electron, the electron moves and photons deflected. |
05:13 | Notice that, spectrum consists of only emitted uv photons. |
05:19 | Turn off the light beam. |
05:23 | Limitations of Plum Pudding model |
05:27 | Here are the limitations of Plum Pudding model. |
05:32 | Based on the above observations, Rutherford proposed the Classical solar system model of atom. |
05:42 | Solar System Model Rutherford nuclear model of an atom is like a small scale solar system. |
05:49 | Nucleus plays the role of sun and the electrons that of revolving planets. |
05:55 | The very small positive charge portion of the atom was called nucleus. |
06:01 | Electrons move around the nucleus. |
06:05 | They move with very high speed in circular paths called orbits. |
06:11 | Back to the simulation. |
06:14 | Pause the simulation. |
06:17 | Click on Classical Solar System from the list. |
06:21 | Screen has Show electron energy level diagram check-box at the top-right corner. |
06:28 | Click on the check box. |
06:31 | It shows the energy of the electron. |
06:35 | If this model were true, it should take an electron only a fraction of a second to spiral into the nucleus. |
06:43 | Turn on the light beam. |
06:46 | Drag the speed slider to slow. |
06:50 | Click on Step button to view the energy of the electron. |
06:55 | Energy of the electron goes from highest to lowest in a fraction of a second. |
07:03 | We know that this does not happen. |
07:07 | Atom is known to be stable. |
07:10 | Turn off the light beam. |
07:13 | Limitations of Solar System model Rutherford model cannot explain, The stability of an atom and also, The distribution of electrons and their energies. |
07:28 | Back to the simulation. |
07:31 | From the Atomic Model list, click on Bohr. |
07:35 | Neils Bohr proposed a model of hydrogen atom to improve upon Rutherford's model. |
07:42 | According to this model, The electron moves around the nucleus in an orbit of fixed radius and energy. |
07:50 | The energy of an electron in the orbit does not change with time. |
07:56 | These orbits are called energy levels. |
08:00 | These orbits are represented by n=1,2,3,4 etc in the Electron energy level diagram. |
08:13 | Turn on the light beam. |
08:15 | Click on Play button. |
08:18 | Initially there is an electron in the 1st orbit of an atom. |
08:23 | Electron energy level diagram shows electron at n =1st level. |
08:29 | Observe the electronic transition in Electron energy level diagram. |
08:34 | Electron absorbs photon and gets excited to higher level. |
08:39 | Energy is emitted when electron moves from higher level to lower level. |
08:45 | This electron returns back to 1st level. |
08:49 | Observe the spectrometer. |
08:52 | Spectrometer shows emitted photons. |
08:56 | Under Light controls, click on Monochromatic radio button. |
09:01 | Then check Show absorption wavelengths checkbox. |
09:05 | You will see four vertical spectral lines. |
09:09 | These lines represent the wavelengths of absorption. |
09:14 | The slider is highlighted on the first line. |
09:18 | Wavelength, 94 nm as shown in the text box. |
09:23 | As the photon strikes the electron, observe the electronic transition at 94 nm in Electron energy level diagram. |
09:32 | The electron moves to n= 6th level. |
09:36 | After a while it moves to lower level by emitting photon. |
09:42 | Turn off the light beam. |
09:45 | As an assignment, Select Bohr Atomic model. |
09:50 | Change the light beam to Monochromatic. |
09:53 | Observe the electronic transitions at 103 nm, 112 nm, and 122 nm absorption wave lengths. |
10:04 | Observe the energy level diagram and the spectrometer results. |
10:09 | Note the observation and give an explanation. |
10:13 | Limitations of Bohr’s model |
10:16 | Bohr's model was unable to explain the following phenomena. |
10:24 | Back to the simulation. |
10:26 | Another model based on dual behavior of electrons was proposed. |
10:32 | Click on de Broglie from the Atomic Model list. |
10:36 | Notice the wave which represents electron in zoom-in box. |
10:42 | deBroglie Atomic Model: The French physicist, de Broglie in 1924 proposed dual behavior of electrons. |
10:51 | Like radiation, matter should also exhibit both particle and wavelike properties. |
10:58 | Electrons should also have momentum as well as wavelength. |
11:03 | Turn on the light beam. |
11:05 | Notice that the electron absorbs photon and moves to higher energy level orbit. |
11:12 | Electron at higher energy level emits energy. |
11:16 | It returns to the lower energy level orbit. |
11:20 | Observe the electronic transitions in energy level diagram. |
11:25 | Top-left corner of the view box has radial view drop-down box. |
11:30 | Click on drop-down arrow. |
11:33 | Scroll to 3D view and click on it. |
11:37 | Now observe the wave nature of electron in 3D view. |
11:42 | Turn off the light beam. |
11:45 | In order to explain the spectrum of hydrogen atom, theory of quantum mechanics came into existence. |
11:53 | Schrödinger Model : Erwin Schrödinger proposed the quantum mechanical model of the atom. |
12:00 | Schrödinger used mathematical equations to describe the probability of finding an electron. |
12:07 | Quantum Numbers: The three coordinates that come from Schrodinger's wave equations are quantum numbers, Principal (n), Angular (l), and Magnetic (m). |
12:19 | Quantum numbers describe size, shape and orientation of the orbitals. |
12:26 | Back to simulation. |
12:29 | Click on Schrödinger from the list. |
12:32 | In the zoom in box, atom is shown with nucleus surrounded by electron cloud. |
12:38 | Switch back to White light. |
12:41 | Turn on the light beam. |
12:43 | Observe that electron absorbs photon and moves to different orbital. |
12:49 | Observe the shapes of orbitals as the electron moves. |
12:54 | Notice the electronic transitions in Electron energy level diagram. |
12:59 | In addition to value of n, energy level diagram has values for l and m also. |
13:06 | Note n, l, m values at the bottom right corner of the view box. |
13:12 | Note the change in n, l, m values as the photons strike the electrons. |
13:19 | All these models compare how the experimental results match with the prediction. |
13:26 | As an assignment, For the Schrodinger's atomic model, select Monochromatic light beam. |
13:34 | Note n,l,m values for the electron at four absorption wavelengths. |
13:41 | Note the orbital shape and possible orientation for each wavelength. |
13:47 | Let us summarize. |
13:49 | In this tutorial we have demonstrated, How to use Models of the Hydrogen Atom, PhET simulation. |
13:59 | Using this simulation we have, Visualized different models of the hydrogen atom. |
14:06 | Explained the experimental predictions of each model. |
14:11 | Discussed limitations of each model. |
14:15 | Determined the orbital shape and orientation from n, l and m values. |
14:22 | Explained the energy level diagram. |
14:25 | The video at the following link summarizes the Spoken Tutorial project. |
14:30 | Please download and watch it. |
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15:11 | This is Meenal Ghoderao from IIT Bombay. |
15:15 | Thank you for joining. |