Contributions to the Development of Models of the Atom

For this assignment, you will be doing some research about scientists who contributed to our current understanding of the atom.  There are many scientists whose discoveries paved the way for all of us who study chemistry.  You will work in groups of two or three and will be assigned one such scientist to research.

Ultimately, your goal is to write a brief story of the contribution to the development of a model of the atom that your scientist made in a way that your group can present to the rest of the class.

For each of the following scientists:

1. introduce the previous model of the atom prior to the scientist’s research
2. the experimental design or data analyzed
3. the evidence (data) that led to a change in the previous model
4. how each scientist developed a new atomic model that incorporated the new evidence OR resolved a flaw in the previous model

You should also find out some interesting tidbits about the scientist's life and weave those into the story you are telling about your assigned contributor.  This is the one opportunity you have in chemistry to be colorful, so take advantage of it!

One class period will be devoted to preparing your story.  Monday, all groups will tell their story to the class and we will create a timeline of contributions and we will trace the "model" of the atom through its historical development.

You will be graded on the content of your presentation and accompanying visual aids or diagrams as well as how well you know your story.  During the presentations of other groups, you will be expected to pay attention, take notes and contribute to this whole class discussion.

Scientists:                                Major Experiment & Contribution:

J.J. Thomson                           Cathode ray tube experiments led to the discovery of the electron and plum pudding model

Ernest Rutherford                   Gold foil experiments led to the discovery of the atomic nucleus and an update to the model of the atom

Robert Millikan                       Oil drop experiments led to additional information about the charge and mass of electrons

Henry Moseley                        Observed x-rays emitted by different elements, which led to the discovery of the atomic number

Sir James Chadwick               Used a beryllium foil experiment to discover another particle in the atom that was hard to find

Niels Bohr                               Observed the emission spectrum of hydrogen to create a model of the atom that now bears his name

Useful URL’s

Timeline (View the proper sequence of the evolution of the model of the atom.)

http://atomictimeline.net/index.php

Here is an overview of the development of the modern model of the atom

http://www.colorado.edu/physics/2000/quantumzone/lines2.html

JJ Thomson

http://atomic-molecular-optical-physics.suite101.com/article.cfm/the_discovery_of_the_electron

http://www.atomicarchive.com/Bios/Thomson.shtml

http://www.chemheritage.org/classroom/chemach/atomic/thomson.html

http://www.chemteam.info/AtomicStructure/Thomson-Model-Intro.html

Rutherford

Follow the instructions while viewing this simulation of Rutherford’s experiment.

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf

Here is another simulation that illustrates the Gold Foil experiment.

http://micro.magnet.fsu.edu/electromag/java/rutherford/

Which atomic model is used to illustrate the experiment ?

Why is this atomic model used instead of the Thompson’s (previous model)?

More information on Rutherford’s Model

http://www.rsc.org/chemsoc/timeline//pages/1911.html

Bohr

http://www.pbs.org/wgbh/aso/databank/entries/bpbohr.html

http://zebu.uoregon.edu/~imamura/208/jan27/hup.html - no longer there...

Oxford dictionary of scientists: http://www.oxfordreference.com/view/10.1093/acref/9780192800862.001.0001/acref-9780192800862-e-161?rskey=a5PXwO&result=161&q=  (might not be accessible outside ASU)

Access same info via: http://www.answers.com/topic/niels-bohr

Model assumptions: http://chemed.chem.purdue.edu/genchem/history/bohr.html

Focus on Origin: http://en.wikipedia.org/wiki/Bohr_model

History, Bohr’s personal life: http://www.nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-bio.html

What were the limitations of Rutherford’s atomic model that prompted Bohr to propose additional features?

Robert Millikan

http://www.juliantrubin.com/bigten/millikanoildrop.html

View this video:

http://video.google.com/videoplay?docid=2799052432147926032&ei=XLEtS-f9HYyQqAKxqbjHBQ&q=millikan+oil+drop+experiment+video&client=safari

Could it be this one: http://www.youtube.com/watch?v=XMfYHag7Liw

This one goes a little further: http://www.youtube.com/watch?v=UFiPWv03f6g

Henry Mosley

http://www.chemteam.info/AtomicStructure/AtNum-AtWtThread.html

http://www.mikeblaber.org/oldwine/chm1045/notes/Periodic/Develop/Period01.htm

http://www.barringtonhighschool.org/Chemistry_Web/Chem history/Mosely/moseley.htm

http://www.chemteam.info/AtomicStructure/AtNum-Moseley.html

http://www.tutorvista.com/content/physics/physics-iv/atoms-and-nuclei/moseleys-law.php

http://www.sooperarticles.com/technology-articles/moseleys-discovery-modern-concept-atomic-number-327.html

James Chadwick

http://atomic-molecular-optical-physics.suite101.com/article.cfm/the_discovery_of_the_neutron

http://www.thocp.net/biographies/chadwick_james.htm

http://www.pbs.org/wgbh/aso/databank/entries/dp32ne.html

http://www.vias.org/physics/bk2_05_05.html

http://www-outreach.phy.cam.ac.uk/camphy/neutron/neutron1_1.htm

Thomson Model of the Atom

J.J. Thomson performed experiments with cathode rays in an attempt to understand electricity – which was still a mystery in the late 1800s. Review the website A Look Inside the Atom http://www.aip.org/history/electron/jjhome.htm to find the conclusions that Thomson and other physicists drew regarding the mysterious cathode rays.

      Thomson’s 1897 Experiments - state the conclusions Thomson drew from each of his famous cathode ray experiments:

1. First Experiment: Thomson directed the beam at an electrometer and tried to separate the evidence of charge from the path of the beam.  What connection did Thomson find between charge and the cathode rays?  Was the charge positive or negative?

2. Second Experiment: Thomson tried passing the cathode ray through an electric field.  How did cathode ray beam behave when it passed through an electric field? What did he conclude after his second experiment?

3. Third Experiment: Thomson did some careful measurements on how much the path of the cathode ray was bent in a magnetic field and how much energy they carried.  From this work Thomson could describe the mass/charge ratio of the cathode ray particles.  What amazing result did Thomson find?

Thomson’s Atomic Model:  Thomson presented three hypotheses from his experiments.  Only two were accepted by physicists – in fact the third was shown to be wrong!  From the first two came a model of the atom known as the Plum Pudding model.  Complete the atom drawing below to illustrate Thomson’s plum pudding model.  Explain how this fits with his observations.

 https://d2gne97vdumgn3.cloudfront.net/api/file/723ZtlYFRcWOOgsLDnQl