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Aug 1, 1000
Democritus
Democritus believed everything was made of extremely small particals that could not be divided. He called them atoms, from a greek word meaning uncut oor invisable. He thougt there were different types of atoms with specific properties. This was done through discussion. (500B.C.) -
Oct 27, 1000
Aristotal
(500 B.C.)
He didn't think there was a limit of times that matter could be divided. He used a model showing all substances built up from four elements - earth, air, fire, and water, and all the elements were a combo of cold, wet, dry, hot. -
John Dalton
Dalton's Theory
-All elements are composed of atoms
-All atoms of the same elements have the same masses, and atoms of different elements have different masses
-Compounds contain atoms of more than one element
-In a particular compound, atoms of different elements always combine in the same way To prove his theory,he made wooden spheres to represent the elements. Each type of atom is represented by a tiny solid spere with a different mass. -
J.J. Thomson
He pictured electrons embedded in a sphere of positive electric charge. He used an electric current to learn more about atoms. He used a device that had a sealed glass tube from which ost of the air has been removed. A metal disc at the end of the tube , wires connect the metal discs to the source of the electric currents. When the current is turned on, one disc become negativley charged, and another postivive. A glowing beam developes between the discs. -
Hantaro Nagoka
Nagoka suggests that an atom has a centeral nucleus, and that electrons move in orbit, like the rings around Saturn. -
Ernest Marsden
Marsden was on of Rutherford's students, he asked him to find out what happens to alpha particals when they pass through a thin sheet of gold. He used the method seen in the diagram to the left. -
Ernest Rutherford
He believed an atom has a dense, positivley charged nucleus. Electrons move randomly in the space around the nucleus. According to his model, all of an atoms positive charge is concentrated in its nucleus. -
Louis de Brogile
He proposes that moving particals, like electrons, have some properties of waves. Within a few years, evidece is collected to support his idea. -
Erwin Schrodinger
Schrodinger developes mathmatical equations to describe the motions of electrons in atoms. His work leads to the deveelopment of the electron cloud model. -
James Chadwick
Chadwick confirms the exsistance of neutrons, which have no charge. Atoms nuclei contain neutrons and positivley charged protons. -
Glen Seaborg
He synthesized six transurnium elements and suggests a change in the periodic table. -
Enrico Fermi
He conducted the first controlled chain reaction releasing enegy from the atoms nucleus. He recieved a Nobel Prize in 1938.
