1. Scientists and Their Contribution to the Model of an Atom
History of the Atom
Scientists and Their Contribution to the Model of an Atom

2. History of the Atom - Timeline
Antoine Lavoisier
makes a substantial number of contributions to the field of Chemistry
J.J. Thomson discovers the electron and proposes the Plum Pudding Model in 1897
Niels Bohr proposes the Bohr Model in 1913
James Chadwick discovered the neutron in in 1932
1766 – 1844
1871 – 1937
1887 – 1961
460 – 370 BC
1700s
1800s
1900s
Erwin Schrodinger describes the electron cloud in 1926
Democritus proposes
the 1st atomic theory
John Dalton proposes his atomic theory in 1803
Ernest Rutherford performs the Gold Foil Experiment in 1909
1891 – 1974
1743 – 1794
1885 – 1962
1856 – 1940
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3. Democritus (460 BC – 370 BC)
Proposed an Atomic Theory (along with his mentor Leucippus) which states that all atoms are small, hard, indivisible and indestructible particles made of a single material formed into different shapes and sizes.
Aristotle did not support his atomic theory
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4. Alchemists (500 BC – 1720)
Now, they wanted to live forever, so they started out with trying to make a potion that could make them live forever.
They didn’t succeed, but they did make many experiments, and the scientific method. They also kept careful records.

5. Image taken from: www.ldeo.columbia.edu/.../v1001/geotime2.html
Antoine Lavoisier (1743 – 1794)
Known as the “Father of Modern Chemistry”
Was the first person to generate a list of thirty-three elements in his textbook
Devised the metric system
Was married to a 13-year old Marie-Anne Pierette Paulze; she assisted him with much of his work
Was a tax-collector that was consequently guillotined during the French Revolution
Discovered/proposed that combustion occurs when oxygen combines with other elements
Discovered/proposed the Law of Conservation of Mass (or Matter) which states, in a chemical reaction, matter is neither created nor destroyed
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6. Image taken from: chemistry.about.com/.../John-Dalton.htm
In 1803, proposed an Atomic Theory which states:
All substances are made of atoms; atoms are small particles that cannot be created, divided, or destroyed.
Atoms of the same element are exactly alike, and atoms of different elements are different
Atoms join with other atoms to make new substances
Calculated the atomic weights of many various elements
Was a teacher at a very young age
Was color blind
Image taken from: chemistry.about.com/.../John-Dalton.htm

7. 1898 Marie & Pierre Curie
They both picked up on Becquerel’s work on uranium, which lead them to find the elements radium and polonium. Though Marie went further with the radioactivity of elements, she didn’t get very far. All she said was, “they were somehow disintegrating over time and emitting radiation that exposed the plate.” ~ Marie Curie
Pierre went on to say that atoms might be composed of even smaller things.

8. Image taken from: chemistry.about.com/.../HenriBecquerel
He described radioactivity. He found this out from unknown x-rays waves, which were produced by uranium.
Penetrating radiation was also discovered by Becquerel.
Discovered that uranium was able to expose a photographic plate on black paper, and didn’t depend on the chemical state.
Image taken from: chemistry.about.com/.../HenriBecquerel

9. 1900 Max Planck
He was the person who came up with the original quantum theory. To come up with this, all he did was research from pervious scientists and a little bit on his own, and then wrote a book on the quantum theory (the theory: the behavior or matter and energy in an atom). He also was looking at color changes from energy. He also made a math equation to help with this theory.

10. 1905 Albert Einstein
First, he found that nature and matter intertwine somehow, the theory of measurement came about from this. Second, he publish 5 papers on electrons. These contributed to the quantum mechanics. He said, “light consists of quanta, bundles of energy which behave somewhat like particles.” ~Albert Einstein

11. 1908 Robert Millikan
He was by far the most famous American scientist. He wanted to find the electrical charge of electrons. He measured water droplets, and that wasn’t successful, so he measured oil droplets, where all this proved electrons were negatively charged. He also was a professor for many years, and wrote many textbooks on chemistry.

12. Image taken from: www.wired.com/.../news/2008/04/dayintech_0430
J.J. Thomson (1856 – 1940)
Proved that an atom can be divided into smaller parts
While experimenting with cathode-ray tubes, discovered corpuscles, which were later called electrons
Stated that the atom is neutral
In 1897, proposed the Plum Pudding Model which states that atoms mostly consist of positively charged material with negatively charged particles (electrons) located throughout the positive material
Won a Nobel Prize
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13. Ernest Rutherford (1871 – 1937)
In 1909, performed the Gold Foil Experiment and suggested the following characteristics of the atom:
It consists of a small core, or nucleus, that contains most of the mass of the atom
This nucleus is made up of particles called protons, which have a positive charge
The protons are surrounded by negatively charged electrons, but most of the atom is actually empty space
Did extensive work on radioactivity (alpha & beta particles, gamma rays/waves) and was referred to as the “Father of Nuclear Physics”
Won a Nobel Prize
Was a student of J.J. Thomson
Was on the New Zealand $100 bill
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14. 1938 Otto Hahn & Lise Meitner
While working in a lab, Otto Hahn discovered radiothorium, and then later discovered 5 more elements. He also discovered radioactive recoil. Lise Meitner was he partner when they discovered the isotope of protactinium. His biggest discovery was barium as a fission element. He combined results with Otto Frisch and they came up with nuclear fission. He was testing uranium and how it busted into lighter elements. Lise always studied radioactivity. She, herself, discovered the auger effect.

15. Image taken from: commons.wikimedia.org/wiki/File:Niels_Bohr.jpg
In 1913, proposed the Bohr Model, which suggests that electrons travel around the nucleus of an atom in orbits or definite paths. Additionally, the electrons can jump from a path in one level to a path in another level (depending on their energy)
Won a Nobel Prize
Worked with Ernest Rutherford
Image taken from: commons.wikimedia.org/wiki/File:Niels_Bohr.jpg

16. Image taken from: nobelprize.org/.../1933/schrodinger-bio.html
Erwin Schrodinger ( )
In 1926, he further explained the nature of electrons in an atom by stating that the exact location of an electron cannot be stated; therefore, it is more accurate to view the electrons in regions called electron clouds; electron clouds are places where the electrons are likely to be found
Did extensive work on the Wave formula  Schrodinger equation
Won a Nobel Prize
Image taken from: nobelprize.org/.../1933/schrodinger-bio.html

17. Image taken from: www.wired.com/.../news/2009/02/dayintech_0227
James Chadwick (1891 – 1974)
Realized that the atomic mass of most elements was double the number of protons  discovery of the neutron in 1932
Worked on the Manhattan Project
Worked with Ernest Rutherford
Won a Nobel Prize
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18. 1951 Glenn T. Seaborg
Glenn was best known for identifying and discovering elements that were heavier then uranium. He also isolated 10 elements. He also proposed the “actinides” in the element table. He discovered these elements just by separating different elements, and combining different elements.

19. 1964 Murray Gell-Mann & George Zweig
Murray Gell- Mann was an American physicist who received a Nobel Prize for his theory on elementary particles. He also found that all the elements of an atom are held together by quarks. To find this, he blasted high speed electrons into a hydrogen atom.
George Zweig proposed the existence of quarks. He thought of them as aces, because he guessed there were four quarks in every atom.
Now, in the same year, both these guys proposed the idea of quarks. They tested electrical charges, and that how the numbers for quarks came about.

20. Werner Heisenberg 1925
Heisenberg Uncertainty Principle – It is impossible to determine the position and velocity of an electron simultaneously.

21. Heisenberg uncertainty principle
In order to observe an electron, one would need to hit it with photons having a very short wavelength.
Short wavelength photons would have a high frequency and a great deal of energy.

22. Democritus & John Dalton
Progression of the Atomic Model + -
The structure of an atom, according to:
Democritus & John Dalton
James Chadwick
J.J. Thomson
Neils Bohr
Ernest Rutherford
Erwin Schrodinger