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460 BCE
Democritus
The theory that everything is composed of atoms, was suggested by Democritus, around 442 B.C.
His concept of the atom included:
-Between every atom there was empty space
-Atoms are indestructible
-There is an infinite number of atoms and kinds of atoms
-Atoms have always been and always will be in motion
-The mass of an Atom described by Democritus, "The more any indivisible exceeds, the heavier it is".
Democritus shaped the idea of the Atom for thousands of years to come. -
John Dalton
In October of 1803 John Dalton suggested the existence of an atom followed by four rules of atoms
-All matter is made of atoms. Atoms are indivisible and indestructible.
-All atoms of given elements are identical in mass and properties.
-Compounds are formed by a combination of two or more different kinds of atoms.
-A chemical reaction is a rearrangement of atoms.
The essence of Dalton's theory remains valid 200 years later. -
JJ Thomson
In April 30, 1897 JJ Thomson suggested there were fundamental units 1,000 times smaller than an atom, known as electrons.
-Corpuscles emerged from the atoms
-Atoms were divisible, corpuscles were their building blocks
In 1904 Thomson suggested a model of an atom
-It was a sphere of positive matter within electrostatic forces
-Corpuscles were distributed in a uniform sea of positive charge
Thomson discoveries of electrons further lead us to the understanding of what atoms are made of. -
Rutherford's Gold Foil Experiment
Rutherford discovered a famous experiment called the
- "Gold Foil Experiment" which required him to take a thin sheet of golf foil, then used special equipment to shoot alpha particles at the foil.
-Most particles passed straight through the foil like the foil, but some didn't pass through, like it was deflected or blocked by something. -
Robert Millikan
In the year 1909 Robert performed the
-"oil drop experiment" to determine the change of electrons. By repeating the oil drop experiment.
-Robert concluded that the charges were multiples of some fundamental value.
-In conclusion, his "oil drop experiment" increased the charge of an electron. In doing so he greatly widened our understanding of the structure of the atom in the Atomic Theory. -
Ernest Rutherford
-Ernest Rutherford concluded that atoms have a small dense center filled with positive charges.
-Ernest named this middle or center the nucleus
-Then he said negative charged electrons surrounded the dense positively charged center or nucleus
-Concluded atoms are mostly empty space
-In conclusion atoms are made of small positive nucleus because positive nucleus repels positive particles -
Niels Bohr
Niels Bohr proposed a theory
-hydrogen atom based on quantum theory that energy is transferred only in defined quantities
-Electrons move around the nucleus in prescribed orbits
-When electrons jump from one ring to another with lower energy, light is emitted.
-In conclusion this concept could explain the reason atoms emit light in fixed wavelengths -
Irwin Schrodinger
The "Electronic Cloud Model" created by Irwin Schrodinger in 1926
-Included a cloud of electrons at different levels in orbit.
-Formed a wave equation that precisely calculated the energy levels of electrons in atoms
-Summary, Irwin's discovered that electrons don't move in orbits. He theorized electrons move in waves, and that they have no exact location. -
Werner Heisenberg
In 1927, Werner Heisenberg proposed the "uncertainty relation", which set limits on how accurately the position and speed of a particle can be determined
-He created his own type of quantum mathematics to explain how the atom worked, and looked.
-In summary, He proposed that "the speed and position of an atom can not be judged at the same time". -
James Chadwick
In 1932 James, bombarded beryllium atoms with alpha particles, unknown radiation was produced.
-James interpreted this radiation as being composed of particles with a neutral electrical charge and the mass of a proton.
-This particles became known as the neutron With the discovery of neutrons, a realistic model of the atom came to light.
-In total, Chadwick discovered the neutron and provided the chemists with an adequate model of the atom.
