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Day 2 |
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Lab |
Vocabulary Test
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Who proposed the first atomic theory? |
Atoms are so small that, even today, direct visual inspection is all but impossible. This picture, taken with an electron microscope, shows the best possible direct observation of iron oxide molecules.
As you can see, details of the atoms cannot be seen. Our model of the atom is based on indirect experimental data. The picture below shows an example of indirect observation. Bullets are shot into the the matchbox and what comes out of the box is observed. From this, a hypothesis can be made about what is inside the box.
For most of the history of science, experimenting was limited to things that were visible to the unaided eye. Today, we have at our disposal devices called acccelerators. 
These complicated machines allow us to "shoot" high energy particles into atoms. Experiments using accelerators give us data to refine our understanding of the atom as well as make new atoms.
Our model of the atom changes as our experimental ability improves. Today's atomic theory tries to explain the observations made with accelerators. The current "quark model" of the atom is a hypothesis based on current atomic theory.
The Greek Model:
Democritus Greek philosopher around the year 400 BC.
Democritus concluded that matter could not be divided into smaller and smaller pieces forever. Eventually, the smallest piece of matter would be found. He used the word atomos to describe the smallest possible piece of matter.
John Dalton English chemist that proposed first atomic theory in 1803.
Points of Dalton's Theory:
- All elements are composed of indivisible particles.
- Atoms of the same element are exactly alike.
- Atoms of different elements are different.
- Compounds are formed by joining atoms of two or more elements.
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A thought experiment is not intended to be carried out as a practical reality, but is "all in the mind". The idea is that by using our understanding of the laws of science we can construct imaginary experiments and predict their outcomes. Albert Einstein was particularly good at inventing thought experiments to test the results of his theory of relativity.
Is the radius of each circle the same? |
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What makes up most of the volume of an atom? |
The Thomson Model:
J. J. Thomson English scientist who discovered electrons in 1897.
Sometimes called the "plum pudding" model, Thomson thought of an atom as being composed of a positively charged material with the negatively charged electrons scattered through it.
Ernest Rutherford British physicist who discovered the nucleus in 1908.
Rutherford's model proposed that an atom is mostly empty space. There is a small, positive nucleus with the negative electrons scattered around the outside edge.
(chem lab 045b) (ps lab 113)
Niels Bohr Danish scientist who proposed the Planetary Model in 1913.
Electrons move in definite orbits around the nucleus, like planets moving around the nucleus. Bohr proposed that each electron moves in a specific energy level.
Sir James Chadwick discovered the neutron in 1935.
Based on wave mechanics, this model proposes that electrons have NO definite path in an atom. The probable location of an electron is based on how much energy it has. The more energy an electron has, the farther from the nucleus. The small, positively charged nucleus is surrounded by a large space in which there are enough electrons to make the atom neutral.
This assignment must be turned in by the end of class today to receive credit.
Scoring criteria
- Write a paragraph explaining how a philosopher is different from a scientist.
- In what years were each of the three basic subatomic particles discovered?
- Which of the atomic models described above are you most familiar with?
- Which atomic model are you most familiar with? Name one thing that troubles you about this model.
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In what year were quarks added to the atomic theory? |
Museum Curator |
The following Nobel Lauretes have contributed to the improvement of our atomic model. The knowledge gained by these scientists has moved us from the Bohr Model, through the Wave Model, and into the Quark Model of the atom. The links are to their page at the Nobel Prize Internet Archive. |
Max Karl Ernst Ludwig Planck
1918 Nobel Laureate in Physics in recognition of the services he rendered to the advancement of Physics by his discovery of energy quanta.
Werner Heisenberg
1932 Nobel Laureate in Physics for the creation of quantum mechanics.
Erwin Schrodinger
1933 Nobel Laureate in Physics for the discovery of new productive forms of atomic theory.
Wolfgang Pauli
1945 Nobel Laureate in Physics for the discovery of the Exclusion Principle.
Robert Hofstadter
1961 Nobel Laureate in Physics for his pioneering studies of electron scattering in atomic nuclei and for his thereby achieved discoveries concerning the stucture of the nucleons.
Richard P. Feynman
1965 Nobel Laureate in Physics for fundamental work in quantum electrodynamics.
Murray Gell-Mann
1969 Nobel Laureate in Physics for his contributions and discoveries concerning the classification of elementary particles and their interactions.
Leon M. Lederman, Melvin Schwartz, and Jack Steinberger
1988 Nobel Laureate in Physics for the demonstration of the doublet structure of the leptons through the discovery of the muon neutrino.
Jerome I. Friedman, Henry W. Kendall, and Richard E. Taylor
1990 Nobel Laureate in Physics for their pioneering investigations concerning deep inelastic scattering of electrons on protons and bound neutrons, which have been of essential importance for the development of the quark model in particle physics.
Martin L. Perl
1995 Nobel Laureate in Physics for the discovery of the tau lepton.
Frederick Reines
1995 Nobel Laureate in Physics for the detection of the neutrino.
The latest information about the quark model will be covered next week.
Test Your Concept Understanding: 
Answer this question with one sentence:
- What energy quanta was discovered by Max Karl Ernst Ludwig Planck.
- What was created by Werner Heisenberg.
- What is the Exclusion Principle described by Wolfgang Pauli?
- Who actually detected (observed) the neutrino?
- Who received a Nobel Prize for his work in quantum electrodynamics?
- Who received the Nobel Prize for Physics in 2000?
Research Links:
John Dalton proposed the first atomic theory in 1803.
Visualize a hollow cone like the one pictured here. Think of slicing it horizontally, parallel to its base. The top of the lower piece is a circle, the bottom of the upper piece is a circle. These two pieces were previously in direct contact, point to point.
