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460
Democritus first thinks of an "atom". (B.C.)
Democritus wondered what would happen if you broke a piece of matter in half, then broke it again, and again and again. When could you break it no further? Democritus thought that it must end at some point, and called this point, atoms.
Aristotle, a Greek Philosopher, dismissed the idea, and the people followed his dismissal. We will not hear any more about atoms until the early 1800's. -
465
The Theory of Democritus & Leucippus (B.C.)
This theory stated that atoms are indestructible and are, and always have been, in motion. They also believed that there are infinite numbers of atoms that come in infinite shapes and sizes.
- "The universe is composed of two elements: atoms and the void in which they exist and move." -
Jan 1, 600
Thales of Miletus makes an important observation (B.C.)
Thales of Miletus discovers that after rubbing a piece of amber with a piece of fur, the amber attracts bits of fur, feathers, and other light particles. He believed the force was from the amber and did not make a connection to an atomic particle. -
John Dalton "sees atoms".
An English Chemist, named John Dalton, was performing experiments with chemicals and they showed matter that had lumpy particles. (Atoms) He realized he had made a discovery that was a part of something bigger. -
John Dalton's Theory and Thoughts
John Dalton proposed 5 statements about atoms:
1) Elements are made of atoms.
2) Atoms of a given element are identical in size, mass, and other properties. Atoms of different elements differ is size, mass, and other properties.
3) Atoms cannot be subdivided, created, or destroyed.
4) Atoms of different elements combine form simple, whole-number ratios to form chemical compounds.
5) In chemical reactions, atoms are combined, seperated, or rearranged. -
John Dalton: More Thoughts
Dalton published his first table of relative atomic weights. (This table has Hydrogen, Oxygen, Nitrogen, Carbon, Sulfur, and Phosphorus.) Hydrogen appears with an atomic weight of 1. There is no record of how Dalton came to that conclusion, except for a Journal entry (9-6-1803) that shows relative weights of atoms. Also, Dalton tried to find the relative diameter of an atom, which he thought all gases were made. To find the answer, he uses the result of chemical analysis. -
Dalton's Atomic Theory
Law of Multiple ProportionsDalton wrote: "The elements of oxygen may combine with a certain portion of nitrous gas or with twice that portion, but with no intermediate quantity"
That statement is the foundation for the Law of Multiple Proportions. (Dalton's third postulate) This law states that the masses of one element which combine with a fixed mass of the second element are in a ratio of whole numbers. -
J.J. Thomson Discovers the Electron and thinks...
The English Physicist discovers the electron and proposes a model for the structure of the atom. Thompson knew electrons had a negative charge and hypothesized that matter must have a positive charge.
-Thomson's model is called "Raisin in the Pudding". -
Joseph John Thompson
Plum Pudding videoIn 1904 Thomson suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces. His efforts to estimate the number of electrons in an atom from measurements of the scattering of light, X, beta, and gamma rays initiated the research trajectory along which his student Ernest Rutherford moved. -
Robert Millikan proves Thomson's Theory
Oil Drop ExperimentThe theory Millikan proved was that the mass of an electron is at least 1000 times smaller than the lightest atom.
How he did it was slightly more complicated.
(Super simple video to help everyone understand.) -
Rutherford VS Thomson
Gold Foil Experiment!http://www.iun.edu/~cpanhd/C101webnotes/modern-atomic-theory/rutherford-model.html
Rutherford is THE REASON why we don't have Plum Pudding diagrams in our class room. He disproved J.J. Thomson's theory with his gold foil experiement and said the diagram would be more similar to planets in orbit.
-Ernest Rutherford won a Nobel Prize in Chemistry. -
J.J. Thompson (and friends)
LEARN ABOUT THE DIFFERENT MODELS OF ATOMS! And their creators! Thomson’s last important experimental program focused on determining the nature of positively charged particles. His techniques led to the development of the mass spectrograph. -
Neils Bohr
Also a Nobel Prize winner!
In 1912, Bohr was working for the Nobel laureate J.J. Thompson in England when he was introduced to Ernest Rutherford, whose discovery of the nucleus and development of an atomic model had earned him a Nobel Prize in chemistry in 1908. Under Rutherford's tutelage, Bohr began studying the properties of atoms. -
Ernest Rutherford is Amazing!
Rutherford was a consummate experimentalist who did everything from discovering alpha and beta rays to help solve problems of submarine detection in WW1.
Rutherford worked with people like Niels Bohr and James Chadwick. He succeeded J.J. Thompson in the Cavendish Professorship at Cambridge. -
Niels isn't Bohr-ing.
1) Combining Rutherford's description of the nucleus and Planck's theory about quanta, Bohr explained what happens inside an atom and developed a picture of atomic structure. This work earned him a Nobel Prize of his own in 1922.
2) Bohr's greatest contribution to modern physics was the atomic model. The Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons.
3) Bohr was the first to discover that electrons travel in separate orbits. -
James Chadwick (...who worked with Ernest Rutherford)
James Chadwick discovered the neutron using evidence collected by Irene Joliot-Curie, who discovered that when beryllium was bombarded with positively charged alpha particles a beam with a high penetrating power was created. James Chadwick discoverd that this beam was not deflected by either electric or magnetic fields, meaning it contained neutral particles- neutrons.
He aslo found that the radius of the nucleus is 10,000 times less than the atom itself. -
Chadwick, Rutherford, Ernest...this is confusing!
But how did this happen?... THIS is how the Neutron came to be! Why should be care?
Neutrons play a huge role in mass and radioactive properties of atoms. Adding Neutrons won't chnage the charge of the atom...but it can make an atom radioactive.
(Side Note: James Chadwick actually won a Nobel Prize in Physics for the discovery of the atom in 1935.) -
Period: to
The Life of an Atom (B.C.)
