-
350
350 B.C - Aristotle
Aristotle modified an earlier
theory that matter was made of four
elements: earth, fire, water, air. -
400
Early Greek Theories• 400 B.C.
Democritus thought matter
could not be divided indefinitely. -
Jan 1, 600
600 B.C. Thales of Miletus
In about 600 B.C. Thales of Miletus discovered that a piece of amber, after rubbing it with fur, attracts bits of hair and feathers and other light objects. Thales did not connect this force with any atomic particle. -
Period: to
John Dalton
1800 -Dalton proposed a modern atomic model
based on experimentation not on pure reason. -
Period: to
Dalton's Atomic Theory
1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms. -
J.J. Thomson (1897)
The English physicist J.J. Thomson discovered the electron and proposed a model for the structure of the atom. Thomson knew that electrons had a negative charge and that matter must have a positive charge. -
Max Planck (1900)
In 1900 Max Planck (Berlin) showed that when you vibrate atoms strong enough you can measure the energy only in discrete units. He called these energy packets, quanta. -
Ernest Rutherford (1911)
Ernest Rutherford thought it would prove interesting to bombard atoms with these alpha rays, figuring that this experiment could investigate the inside of the atom.He used Radium as the source of the alpha particles and shinned them onto the atoms in gold foil; he could observe the alpha particles impact. -
Niels Bohr (1912)
Niels Bohr came up with a theory that said the electrons do not spiral into the nucleus and came up with some rules for what does happen. -
Ernest Rutherford (1919)
Not until 1919, Rutherford finally identify the particles of the nucleus as discrete positive charges of matter. Using alpha particles as bullets, Rutherford knocked hydrogen nuclei out of atoms of six elements: boron, fluorine, sodium, aluminum, phosphorus, an nitrogen. He named them protons. He found the protons mass at 1,836 times as great as the mass of the electron. -
Bohr's model (1920's)
Further experiments showed that Bohr's model of the atom had some troubles. Bohr's atom seemed too simple to describe the heavier elements (in fact it only worked roughly in these cases). -
Wolfgang Pauli (1924)
Wolfgang Pauli predicted that an electron should spin while it orbits around the nucleus. The electron can spin in either of two direction. This spin consisted of a fourth quantum number: electron spin (s). -
Louis de Broglie (1924)
Louis de Broglie thought that if light can exist as both particles and waves, why couldn't atom particles also behave like waves? In a few equations derived from Einstein's famous equation, (E=mc2) he showed what matter waves would behave like if they existed at all. -
Erwin Schrödinger (1926)
Erwin Schrödinger had an idea: Why not go all the way with particle waves and try to form a model of the atom on that basis? His theory worked kind of like harmonic theory for a violin string except that the vibrations traveled in circles. -
Max Born (1926)
Max Born had an idea about 'psi'. He thought they resembled waves of chance. These ripples moved along waves of chance, made up of places where particles may occur and places where no particles occured. -
Bohr’s model
There are 2 types of spectra: continuous spectra & line spectra. It’s when electrons fall back down that they release a photon. These jumps down from “shell” to “shell” account for the line spectra seen in gas discharge tubes (through spectroscopes).
• Electrons orbit the nucleus in “shells”
• Electrons can be bumped up to a higher
shell if hit by an electron or a photon of light. -
Heisenberg (1927)
Heisenberg formulated an idea, which agreed with tests, that no experiment can measure the position and momentum of a quantum particle simultaneously. This implies that as one measures the certainty of the position of a particle, the uncertainty in the momentum gets correspondingly larger. Or, with an accurate momentum measurement, the knowledge about the particle's position gets correspondingly less. -
Period: to
Paul Dirac
Paul Dirac produce equations which predicted an unthinkable thing at the time- a positive charged electron. In 1932 in experiments with cosmic rays, Carl Anderson discovered the anti-electron, which proved Dirac's equations -
James Chadwick (1932)
Not until 1932 James Chadwick finally discover the neutron. He found it to measure slightly heavier than the proton with a mass of 1840 electrons and with no charge (neutral). The proton-neutron together, received the name, "nucleon." -
Werner Heisenberg (1932)
In 1932, Werner Heisenberg concluded that charged particles bounce photons of light back and forth between them. This exchange of photons provides a way for the electromagnetic forces to act between the particles. These photon exchanges go on all the time, very rapidly. -
Hideki Yukawa (1935)
In 1935 Hideki Yukawa, suggested that exchange forces might also describe the strong force between nucleons. However, virtual photons (not real) did not have enough strength for this force, so he thought that there must exist a new kind of virtual particle. Yukawa used Heisenberg's uncertainty principle to explain that a virtual particle could exist for an extremely small fraction of a second. -
Richard Feynman, Julian Schwinger, Sin-Itiro (1940's)
The theory called "quantum electrodynamics," or QED, developed from work by Richard Feynman, Julian Schwinger, and Sin-Itiro in the late 1940s. -
Cecil F. Powell (1947)
In 1947Cecil F. Powell detected this particle and called it the "pion." -
Period: to
Physicists
From 1947 until the end of the 1950's, physicists discovered many more new particles. The various types of particles needed a new theory to explain their strange properties. -
Physicists (1955)
In 1955, physicists found the anti-proton, and later the anti-neutron. This allows the existence for anti-atoms, a true form of antimatter. -
Murray Gell-Mann and Yuval Ne'man (1960)
Murray Gell-Mann and Yuval Ne'man independently proposed a method for classifying all the particles then known. The method became known as the Eightfold Way. -
Gell-Mann (1964)
Gell-Mann went further and proposed the existence of a new level of elementary particles and called them "quarks" (the spelling derives from a phrase in James Joyce book, Finnegans Wake, "Three quarks for Muster Mark.