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Period: 500 to 505
Democritus
Democritus was a Greek philosopher. He was the first person to suggest that matter cannot be infinitvely divided. He invented the term "atomos". This term was used to describe tiny particles that make up matter. He thought atomos could only move through empty space. He also came up with the quote "Atomos cannot be created, destroyed, or further divided." -
Period: 550 to Aug 25, 600
Aristotle
Aristotle was another greek philosopher. He disagreed with Democritus' idea that atoms move through empty space. He set some scientist back because he denied the existence of atoms due to his personal ideas about nature. -
Period: to
John Dalton
Dalton was a school teacher who started the idea of the modern atomic theory. He based and revised Democritus' ideas on matter and combined his own scientific research. He revised the term "atomos" to "atoms". He claimed "atoms are the smallest particles of matter and are indivisible and indestructible". -
Acceptance
Dalton's ideas about the atomic theory were accepted because it was able to explain the conservation of mass. The theory presented as "atoms can be rearranged, separated, or combined to form new things, but cannot be created, destroyed, or divided in the process." -
Period: to
Determining the Charge of the Electron
American physicist Robert Millikan designed an oil drop to determine the charge of the electron. The charge was equated to a single unit of negative charge. The electron carries a charge of negative one. -
More discovery
Since Dalton's atomic theory was introduced atoms have been proven existent.
Definition of an atom: The smallest particle of any element that retains the property of that element.
Individual atoms can be seen when using an STM. The Cathode Ray Tube consists of glass tubes with air removed from the inside chamber connected to an electrical source via a cathode and an anode. The Cathrode Ray Tube helped researchers study the relationship between mass and charge. -
More on Cathode Rays
Research on the cathode ray tubes lead scientist to the idea that cathode rays were a stream of charged particles and that the particles carried a negative charge. The negative particles were later found to be elections. -
Nucleus
Rutherford came to the conclusion that Thompson's plum pudding model of the atom was incorrect. He claimed that there needed to be a tiny region in the center of the atom and he called that spot the nucleus. -
Proton and Neutron
Rutherford concluded that the nucleus contained protons. Protons are positively charged particles. James Chadwhick demonstrated that the nucleus had the neutron. Neutron are subatonic particles that carry no electric change and weigh just the same as a proton. -
Completing the Model of an Atom
Atoms consist of three particles; electrons, protons, and neutrons. Atoms are spherically shaped with small dense positively charged nuecleus. The nucleus is only about 1/10000 of the atom it occupies. -
The Model
JJ Thompson shared a model of an atom that sharred a uniform positive charge. The negatively charged electrons were simular to the characteristics of a plum. -
1976 Cont.
Sir William Crookes noticed a green light within a cathode ray tube while working in a dark lab. The striking of radiation inside the tube lead to a discovery that the radiation went completely through the tube and not only the Zn-S coding. These were noted as "cathode rays." This later lead to the discovery of television.
