View source for PhET-Simulations-for-Chemistry/C3/Models-of-Hydrogen-atom/English-timed


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||'''Time'''
||'''Narration'''

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|| 00:01
|| Welcome to the spoken tutorial on '''Models of the hydrogen atom'''.

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|| 00:07
|| In this tutorial we will, Demonstrate '''Models of the Hydrogen Atom''', '''PhET simulation'''.

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|| 00:16
|| Here I am using-Ubuntu Linux OS v 14.04

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|| 00:24
||Java v 1.7.0

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|| 00:29
|| To follow this tutorial, Learner should be familiar with topics in high school science.

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|| 00:37
|| Using this '''simulation''' we will, Visualize different models of the hydrogen atom.

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|| 00:44
||Explain the experimental predictions of each model.

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|| 00:49
||Discuss limitations of each model.

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|| 00:53
|| Explain the energy level diagram.

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|| 00:56
||Determine the orbital shape and orientation from n, l and m values.

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|| 01:03
|| Let us start the demonstration.

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||01:06
|| Use the given link to download the '''simulation'''.

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||01:11
|| I have already downloaded '''Models of the Hydrogen Atom simulation''' to my '''Downloads''' folder.

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|| 01:18
|| To run the '''simulation''', open the terminal.

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|| 01:22
||At the prompt type '''cd space Downloads''' and press '''Enter'''.

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|| 01:29
|| Then type, '''java space hyphen jar space hydrogen hyphen atom_en.jar''' and press '''Enter'''.

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|| 01:41
||'''Models of the Hydrogen Atom simulation''' opens.

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|| 01:45
|| Top-left corner of the screen has a menu bar with menu items '''File''' and '''Help'''.

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|| 01:52
|| Below the menu bar, there is a grey button with two options, '''Experiment''' and '''Prediction'''.

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|| 02:01
|| By default '''Experiment''' mode opens.

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|| 02:05
|| On the screen, we see an experimental setup with a light gun to emit beam of photons.

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|| 02:13
|| There is also a '''Box of Hydrogen'''.

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|| 02:16
||This box is filled with hydrogen atoms. 

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|| 02:20
||The zoom-in box represents a single hydrogen atom.

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|| 02:25
|| A message appears.

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|| 02:28
||It prompts you to click on the red button to turn on the light beam.

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|| 02:33
|| The light gun has two light controls, '''White''' and '''Monochromatic'''.

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|| 02:41
||By default '''White''' light is selected.

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|| 02:45
|| Click on '''Prediction''' option on the grey button. 

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|| 02:49
||'''Atomic Model''' panel opens on the left-side of the screen.

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|| 02:54
||It has a list of '''Classical''' and '''Quantum Atomic Models'''.

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|| 02:59
|| Here we can check how the prediction of a model matches the experimental results.

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|| 03:06
|| '''Legend''' box on the right-side of the screen has a list of sub-atomic particles.

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|| 03:13
|| At the bottom of the screen we have, Slider to control speed of animation '''Play'''/'''Pause''' and '''Step''' buttons.

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|| 03:25
|| The first model of atom proposed, is the '''Billiard Ball''' model.

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|| 03:30
||By default '''Billiard Ball''' is selected from the list.

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|| 03:35
|| '''Billiard Ball''' Model

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|| 03:38
||'''Billiard Ball''' model is also called as '''Dalton's''' atomic model. 

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|| 03:44
||It was proposed by '''John Dalton'''.

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|| 03:48
||According to this model, individual atom is visualized as solid, hard spheres, like billiard balls.

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|| 03:58
|| Click on the red button of the light gun.

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|| 04:02
||Select '''White''' light.

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||04:05
|| A beam of photons having different wave lengths pass through box of hydrogen.

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|| 04:11
|| Observe that, All photons in the path of hydrogen atoms are deflected.

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||04:17
|| Limitations of '''Billiard Ball''' model.

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|| 04:21
||Here are the limitations of '''Billiard Ball''' model.

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|| 04:27
|| Back to the '''simulation'''.

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|| 04:30
||Turn off the light beam.

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|| 04:33
||Click on '''Plum Pudding''' from the '''Atomic Model''' list.

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|| 04:37
|| This model was proposed by '''J. J. Thomson''' in 1898.

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|| 04:43
||The positive charge is uniformly distributed and electrons are embedded into it.

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|| 04:50
||The brown mass is the positive charge.

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|| 04:53
||Blue color particle in the middle is the electron.

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|| 04:57
|| Click on '''Show spectrometer''' check-box.

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|| 05:01
||Turn on the light beam.

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|| 05:04
||Select '''White''' light.

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|| 05:07
|| When photons strikes electron, the electron moves and photons deflected.

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|| 05:13
||Notice that, spectrum consists of only emitted uv photons.

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|| 05:19
|| Turn off the light beam.

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|| 05:23
|| Limitations of''' Plum Pudding model'''

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|| 05:27
||Here are the limitations of '''Plum Pudding''' model.

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|| 05:32
|| Based on the above observations, Rutherford proposed the '''Classical solar system''' model of atom.

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|| 05:42
|| '''Solar System''' Model Rutherford nuclear model of an atom is like a small scale solar system.

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|| 05:49
||Nucleus plays the role of sun and the electrons that of revolving planets.

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|| 05:55
|| The very small positive charge portion of the atom was called nucleus.

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|| 06:01
||Electrons move around the nucleus.

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|| 06:05
||They move with very high speed in circular paths called orbits.

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|| 06:11
|| Back to the '''simulation'''.

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|| 06:14
||Pause the '''simulation'''.

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|| 06:17
||Click on '''Classical Solar System''' from the list.

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|| 06:21
|| Screen has '''Show electron energy level diagram''' check-box at the top-right corner.

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|| 06:28
||Click on the check box.

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|| 06:31
||It shows the energy of the electron.

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|| 06:35
|| If this model were true, it should take an electron only a fraction of a second to spiral into the nucleus.

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|| 06:43
|| Turn on the light beam.

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|| 06:46
|| Drag the speed slider to '''slow'''.

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|| 06:50
|| Click on '''Step''' button to view the energy of the electron.

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|| 06:55
||Energy of the electron goes from highest to lowest in a fraction of a second.

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|| 07:03
|| We know that this does not happen.

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|| 07:07
||Atom is known to be stable.

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|| 07:10
||Turn off the light beam.

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|| 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.

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|| 07:28
|| Back to the '''simulation'''.

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|| 07:31
||From the '''Atomic Model''' list, click on '''Bohr'''.

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|| 07:35
||'''Neils Bohr''' proposed a model of hydrogen atom to improve upon '''Rutherford's''' model.

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|| 07:42
|| According to this model, The electron moves around the nucleus in an orbit of fixed radius and energy.

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|| 07:50
||The energy of an electron in the orbit does not change with time.

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|| 07:56 
||These orbits are called energy levels.

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|| 08:00
||These orbits are represented by '''n=1,2,3,4''' etc in the '''Electron energy level''' diagram.

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|| 08:13
|| Turn on the light beam.

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|| 08:15
||Click on '''Play''' button.

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|| 08:18
|| Initially there is an electron in the 1st orbit of an atom.

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|| 08:23
||'''Electron energy level''' diagram shows electron at n =1<sup>st </sup>level.

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|| 08:29
|| Observe the electronic transition in '''Electron energy level''' diagram. 

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|| 08:34
||Electron absorbs photon and gets excited to higher level.

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|| 08:39
||Energy is emitted when electron moves from higher level to lower level.

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|| 08:45
|| This electron returns back to 1<sup>st</sup> level.

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|| 08:49
|| Observe the spectrometer.

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|| 08:52
||Spectrometer shows emitted photons.

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|| 08:56
|| Under '''Light controls''', click on '''Monochromatic''' radio button.

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|| 09:01
|| Then check '''Show absorption wavelengths''' checkbox.

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|| 09:05
|| You will see four vertical spectral lines.

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|| 09:09
||These lines represent the wavelengths of absorption. 

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|| 09:14
|| The slider is highlighted on the first line.

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|| 09:18
||Wavelength, '''94 nm''' as shown in the text box.

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|| 09:23
|| As the photon strikes the electron, observe the electronic transition at '''94 nm''' in '''Electron energy level''' diagram.

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|| 09:32
|| The electron moves to n= 6<sup>th</sup> level.

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|| 09:36
||After a while it moves to lower level by emitting photon.

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|| 09:42
|| Turn off the light beam.

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|| 09:45
|| As an assignment, Select '''Bohr''' Atomic model.

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|| 09:50
||Change the light beam to '''Monochromatic'''.

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|| 09:53
||Observe the electronic transitions at 103 nm, 112 nm, and 122 nm absorption wave lengths.

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||10:04
||Observe the energy level diagram and the spectrometer results.

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||10:09
||Note the observation and give an explanation.

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||10:13
||Limitations of '''Bohr’s''' model

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||10:16
||'''Bohr's''' model was unable to explain the following phenomena.

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|| 10:24
|| Back to the '''simulation'''.

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|| 10:26
||Another model based on dual behavior of electrons was proposed.

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||10:32
|| Click on '''de Broglie''' from the '''Atomic Model''' list.

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||10:36
||Notice the wave which represents electron in zoom-in box.

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||10:42
||'''deBroglie''' Atomic Model: The French physicist, '''de Broglie''' in 1924 proposed dual behavior of electrons.

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||10:51
||Like radiation, matter should also exhibit both particle and wavelike properties.

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|| 10:58
||Electrons should also have momentum as well as wavelength.

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|| 11:03
|| Turn on the light beam.

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|| 11:05
|| Notice that the electron absorbs photon and moves to higher energy level orbit.

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|| 11:12
||Electron at higher energy level emits energy.

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|| 11:16
||It returns to the lower energy level orbit.

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|| 11:20
||Observe the electronic transitions in '''energy level diagram'''.

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|| 11:25
|| Top-left corner of the view box has '''radial view''' drop-down box.

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|| 11:30
||Click on drop-down arrow.

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|| 11:33
||Scroll to '''3D view''' and click on it.

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|| 11:37
|| Now observe the wave nature of electron in '''3D view'''.

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|| 11:42
||Turn off the light beam.

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|| 11:45
|| In order to explain the spectrum of hydrogen atom, theory of quantum mechanics came into existence. 

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|| 11:53
|| '''Schrödinger''' Model : '''Erwin Schrödinger''' proposed the quantum mechanical model of the atom.

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|| 12:00
||'''Schrödinger''' used mathematical equations to describe the probability of finding an electron.

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||12:07
|| '''Quantum''' Numbers: The three coordinates that come from '''Schrodinger's''' wave equations are '''quantum''' numbers, '''Principal (n)''', '''Angular (l)''', and '''Magnetic (m)'''.

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|| 12:19
||'''Quantum''' numbers describe size, shape and orientation of the orbitals.

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|| 12:26
|| Back to '''simulation'''. 

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|| 12:29
||Click on '''Schrödinger''' from the list.

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|| 12:32
||In the zoom in box, atom is shown with nucleus surrounded by electron cloud.

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|| 12:38
|| Switch back to '''White''' light.

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|| 12:41
|| Turn on the light beam.

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|| 12:43
|| Observe that electron absorbs photon and moves to different orbital.

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|| 12:49
|| Observe the shapes of orbitals as the electron moves.

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|| 12:54
|| Notice the electronic transitions in '''Electron energy level''' diagram. 

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|| 12:59
||In addition to value of '''n''', '''energy level''' diagram has values for '''l''' and '''m''' also.

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|| 13:06
|| Note '''n''', ''' l''', '''m''' values at the bottom right corner of the view box.

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|| 13:12
||Note the change in '''n''', '''l''', '''m''' values as the photons strike the electrons.

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|| 13:19
|| All these models compare how the experimental results match with the prediction.
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|| 13:26
|| As an assignment, For the '''Schrodinger's''' atomic model, select '''Monochromatic''' light beam.

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|| 13:34
||Note '''n,l,m''' values for the electron at four absorption wavelengths.

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|| 13:41
||Note the orbital shape and possible orientation for each wavelength.

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||13:47
|| Let us summarize.

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|| 13:49
||In this tutorial we have demonstrated, How to use '''Models of the Hydrogen Atom''', ''' PhET simulation'''.

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|| 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.

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|| 14:15
|| Determined the orbital shape and orientation from '''n''', '''l''' and '''m''' values.

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|| 14:22
||Explained the energy level diagram.

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|| 14:25
|| The video at the following link summarizes the Spoken Tutorial project.

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|| 14:30
||Please download and watch it.

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|| 14:33
|| The '''Spoken Tutorial Project''' team: conducts workshops using spoken tutorials and gives certificates on passing online tests.

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|| 14:42
||For more details, please write to us.

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|| 14:46
|| Please post your timed queries in this forum.

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|| 14:51
|| This project is partially funded by Pandit Madan Mohan Malaviya National Mission on Teachers and Teaching.

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|| 14:59
|| Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India.

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|| 15:06
||More information on this mission is available at this link.

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|| 15:11
|| This is Meenal Ghoderao from IIT Bombay.

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|| 15:15
||Thank you for joining.
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|}