-
460
Democritus
460 BC- 370 BC
Some things he discovered:
*Believed matter was made up of tiny particles called atoms. Atoms could not be destroyed, created or further divided.
*matter is composed of empty space through which atoms move.
*different kinds of atoms have different shapes and sizes and different properties are due to this -
Dalton
6 September 1766 – 27 July 1844
Some things he discovered:
*studied numerous chemical reactions, making careful observations ad measurements along the way
*proposed his atomic theory in 1803
*All matter is composed of extremely small particles called atoms
*different atoms combine in simple whole-number ratios to form compounds
*in a chemical reaction, atoms are separated, combined or rearranged -
JJ Thomson
18 December 1856 – 30 August 1940
Some things he discovered:
*Discovered the electron using a cathode-ray tube
*concluded that the rays negative particles were found in all forms of matter -
Ernest Rutherford
30 August 1871 – 19 October 1937
Some things he discovered:
*discovered the nucleus of atoms during his gold foil experiment
*atom contains tiny dense center called nucleus
*nucleus is essentially the entire mass of the atom
*nucleus is positively charged
*electrons move around in the empty space of the atom surrounding the nucleus -
Henry Moseley
23 November 1887 – 10 August 1915
Some information he discovered:
*discovered that atoms of each element contain a unique positive charge in their nuclei
*number of protons in an atom identifies it as an atom of a particular element
*number of protons and electrons in an atom must be equal for an atom to be neutral
*atomic number= number of protons which equals number or electrons -
aristotle
384-322 BC
Some things he discovered:
*denied the existence of atoms
*One of his major criticisms concerned is the idea that atoms moved through empty space.
*Did not believe that the nothingness of empty space could exist
