Group3

Group 3: Sarah, Sam, MacKenzie, Brook = = =__**Joseph John Thomson:**__**by Sarah**= < Picture from: "J. J. Thomson - Wikipedia, the free encyclopedia." //Wikipedia, the free encyclopedia//. N.p., n.d. Web. 18 Sept. 2011. <http://en.wikipedia.org/wiki/J._J

Atom Picture from: "Chemistry: The Central Science, chapter 2, section 2." //Chemistry: The Central Science//. N.p., n.d. Web. 18 Sept. 2011. <wps.prenhall.com/wps/media

J.J. Thomson, who actually became a physicist by default, since his dad wanted him to be an engineer, which meant he had to do an apprenticeship, and his family couldn't afford that, so he went to Owen's College in Manchester, which had a great science faculty. Later on, he attended Trinity College in Camebridge, where he actually became a mathematical physicist. Thomson is great at lecturing, and was a very devoted scientist J.J. Thomson received many different honours such as: Nobel Prize in Physics (1906) and a Knighthood (1908)

In 1904, Thomson thought the atom was a sphere of positive matter, where electrons were positioned by electrostatic forces. Thomson actually discovered the electron when he was doing some experiments to study the nature of the electric discharge high-vacuum cathode-ray tube an area many others were experimenting with too. Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of bodies "much smaller than atoms". He later found them as having a very large value for the charge-to-mass ratio. Later on he guessed the value of the charge.

all info from:

" Joseph John Thomson | Chemical Heritage Foundation." //Homepage of the Chemical Heritage Foundation | Chemical Heritage Foundation//. N.p., n.d. Web. 19 Sept. 2011. [].

STRENGTHS: - found that it's a positively charged sphere - found that the atom is made up of smaller particles - He found that electrons were scattered through it

WEAKNESSES: - Didn't find the nucleus - Didn't find that electrons surround the nucleus, and take up most of the atoms space - didn't find that the electrons are in specific energy levels around the nucleus

__**Ernest Rutherford**__
Reference: []

Gold Foil experiment
Ernest Rutherford in 1909 started an experiment using x-ray technology by using a sheet of gold 1/3000 of an inch thick and shooting radioactive waves (or alpha rays that were caused by the element radium) at it and tracing if the particles path’s. By this he found that most of the particles had gone through the gold foil but not all of them did there was an occasional time when a few particles bounced back. Now from that he stated that atoms have all it mass and a positive charge in the center of the nucleus. This is 10,000 times smaller than the atom itself. After that he figured all negative charge is found orbiting the nucleus like planets around the sun. (Reference: [] )

A picture of Rutherford’s Atomic Theory as a Carbon (Reference: [] )



Rutherford model of his atomic theory Gold Foil Experiment (Reference: [] /M.Schmidt%2BTime%2BLine%2BProject&docid=awpn_XbxkwroDM&w=380&h=310&ei=Z-N0TveUGIbfsQLZ0pGMBQ&zoom=1&biw=1366&bih=555&iact=rc&dur=4&page=1&tbnw =108&tbnw=132&start=0&ndsp=25&ved=1t:429,r:0,s:0&tx=90&ty=76 )



People who helped with this theory: Hans Geiger and E. Marsden-studied radiation with Rutherford J.J. Thompson-Ernest Rutherford Worked under J.J. Thompson on the electrical conduction of air when in the presence of an X-Ray. (Reference to these names: [] ) [|Niels Bohr], [|James Chadwick], and [|Robert Oppenheimer]-These men all worked under Rutherford on his way to discovering something new in the atomic theory.

Strengths and Weaknesses Strengths: -electrons move fast through the atom. -electrons are trapped within the atom by a positively charged nucleus -electrons are negatively charged. Weaknesses: -failed to discover the nucleus contains protons (which are positively charged particles) -failed to discover the nucleus also contains neutrons (a neutral particle)

__**Bohr Model**__

In 1913, Danish physicist Niels Bohr explained the spectrum of a hydrogen atom by combining Rutherford’s model with the Quantum theory. He came to the conclusion that all negatively charged electrons circulate around the positively charged nucleus in a stable orbit. This was big news to the world considering this was the first explanation of the atomic spectrum of the hydrogen atom. Although Bohr’s original model was not actually 100% correct, it was because of it that scientists have been able to evolve the theory into a more accurate model.

The Bohr diagram of an atom consists of a nucleus in the middle with energy levels or “orbitals” circulating. These energy levels carry electrons which circulate or “orbit” the nucleus. The amount of electrons aloud on each energy level depends on the amount of elements in each period of the periodic table. For example, since there are only two elements in the first period, only two electrons are able to be on the first orbital.

Neils Bohr developed his theory and model from the earlier explanation of the atomic structure, by Ernest Rutherford. Although Rutherford did also come to the conclusion that electrons did orbit a positively charged nucleus, he also came up with the theory that by time, the electrons would omit electromagnetic radiation and lose energy, causing them to move closer to the nucleus. This would also mean that as the electrons lost energy the amount of radiation emitted would decrease.

Through studies and experiments, Bohr eventually proved some parts of the Rutherford model wrong, and was able to evolve the theory into a more accurate explanation. Bohr came to the conclusion that electrons may only travel in certain classical movements. This means that electrons travel in certain ways that can be predicted and are not random. The electrons travel on energy levels very small distances away from the nucleus. Every orbital has its own specific energy level. The electrons travel in predictable orbits, which means they will not lose or gain energy unless they jump from one orbital to another.

Pros/Cons:


 * Fails to explain important key notes
 * Violates “uncertainty principle” – the model explains electrons to have a consistent orbit and same radius, which is impossible to know at the same time
 * Was the first model to explain the spectrum of a hydrogen atom
 * Bohr’s model makes it difficult to explain or draw some of the larger atoms
 * Cannot say why some energy levels are certain lengths from each other
 * Model does not work for (neutral) helium because it is a multi electron atom and does not have the energy levels that are predicted by the model
 * Makes the basic atomic spectrum easy to understand
 * Simple to draw any element on the periodic table using the Bohr diagram

Majority of Bohr’s finding came from experiments conducted using electric discharges through low-pressure gasses in glass tubes.



Since the Bohr diagram, there have been several changes/enhancements made. The most famous model created since the Bohr diagram is the Sommerfeld model. The key change between the two models is that the once thought circular orbitals Bohr had explained in his model were now proclaimed to be elliptical, which means the electrons travel on not so perfect "elliptical" orbitals. Sommerfeld's model did a better job of explaining the structure of an atom because it was now clear that the energy levels were not neccessarily kept consistant and were not just simple circles. The main mistake Bohr when creating his atomic spectrum was violating what is called the "uncertainty priciple", which means the electrons cannot have a consistent orbit or same radius between orbitals.

Bibliography (created using Bibme.org):

<span style="font-family: 'Times New Roman','serif'; font-size: 13px;">-"Bohr model - Wikipedia, the free encyclopedia." //Wikipedia, the free encyclopedia//. N.p., n.d. Web. 10 Oct. 2011. <http://en.wikipedia.org/wiki/Bohr_model#Shortcomings>.

<span style="font-family: 'Times New Roman','serif'; font-size: 13px;">-Helmenstine, Anne Marie, and Ph.D.. "Bohr Model - Bohr Model of the Atom." //Chemistry - Periodic Table, Chemistry Projects, and Chemistry Homework Help//. N.p., n.d. Web. 10 Oct. 2011. <http://chemistry.about.com/od/atomicstructure/a/bohr-model.htm>.

<span style="font-family: 'Times New Roman','serif'; font-size: 13px;">-"Niels Bohr - Biography." //Nobelprize.org//. N.p., n.d. Web. 10 Oct. 2011. <http://www.nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-bio.html>.

<span style="font-family: 'Times New Roman','serif'; font-size: 13px;">-"Niels Bohr - Wikipedia, the free encyclopedia." //Wikipedia, the free encyclopedia//. N.p., n.d. Web. 10 Oct. 2011. <http://en.wikipedia.org/wiki/Niels_Bohr>.

=<span style="font-family: 'Times New Roman','serif'; font-size: 13px;">By: Sam Folkersen =

Group assessment:

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">What model was the successor to the Bohr model and why did the Bohr model fail? :

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Since the Bohr diagram, there have been several changes/enhancements made. The most famous model created since the Bohr diagram is the Sommerfeld model. The key change between the two models is that the once thought circular orbitals Bohr had explained in his model were now proclaimed to be elliptical, which means the electrons travel on not so perfect "elliptical" orbitals. Sommerfeld's model did a better job of explaining the structure of an atom because it was now clear that the energy levels were not neccessarily kept consistant and were not just simple circles. The main mistake Bohr when creating his atomic spectrum was violating what is called the "uncertainty priciple", which means the electrons cannot have a consistent orbit or same radius between orbitals

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Between the Dalton model and the Bohr model, many things have changed and evolved you could say. To start off, in the eary 1800's when John Dalton found that all matteris made of these small things called atoms, he found that each different atom of a different element, have different properties, he also found that if you add two or more elements together you can make a new substance. Now later on, as science progressed, J.J. Thomson came along, and looked further into atoms and found that each atom has even smaller particles! He also found that the atom is a sphere shape, which is positively charged and has electrons scattered throughout it! Now fast forward to 1911, when Earnest Rutherford comes along with even better technology, and can now look even deeper into the atom, he comes up with the"Gold Foil Experiment" and finds that all of the tiny atoms positive charge comes from this tiny point in the centre of that atom callled the nucleus, he also found that electrons surround that nucleus, and take up most of the atoms volume, but only make a small fraction of the mass. fast foreard two more years to 1913, when mr. Neils Bohr comes around and figures he'll look even deeper into this atom thing, and finds that electrons are not just outside of the atom, but they are in specific energy levels aroun d the atom, he also finds that the maximum number of electrons in each of those first three energy levels are two, then eight, then eight. Now we're in modern times, in the 2000's and we've now found that electrons do NOT exist as tiny llittle points outside of the atom, but that electrons exist in energy levels, now without the Bohr model, we wouldn't know that! So basically one thing leads to another in the evolution of atom models, and each scientist helped out one another by finding something more and more. (: