Atomic Theory Thru the Ages

Democritus

460

Democritus lived from 460 BC to 370 BC, and he thought matter could not be infinitely divided. He came up with the term atomos. This is how we got the term atom. He used this to decribe tiny particles that make up matter and move through empty space. He thought atoms can not be created, destroyed, or further divided. He had a problem though, he could not figure out what atoms were made of.

Aristotle

500

Aristotle lived from 384 BC to 322 BC. He disagreed with Democritus' idea that atoms move through empty space. He denied the existence of atoms. His ideas took over Democritus' and moved back to square one.

Dalton

520

John Dalton lived from 1766 to 1844. He marked the development of the modern atomic theory. He took Democritus' ideas and revised them based off of his research. He revived the term atom to be the smallest particles of matter and are indivisable and indestructible. This theory was used to explain the conservation of mass. Since Dalton's theory, the existence of atoms has been proven.

Sir William Croockes

540

SIr WIlliam Croockes (1832-1919) noticed a green light in a cathode tub. It was later discovered that the radiation went completely through the tube. His discovery later led to the television. Scientists continued to research the cathode ray tubes and this led them to the idea that the rays were a stream of charged particles. It was finally concluded that the particles were electrons.

JJ Thompson

560

JJ Thompson was born in 1856 and died in 1940. Thompson design experiments to find the ratio of the Cathode ray particle's charge to its mass. This led to information that went against Dalton's theory that atoms were indivisible. He is recognized for the discovery of the first subatomic particle which was the electron. He thought of the atom as a positive charge all over and electrons inside. This was the plum pudding model.

Ernest Rutherford

Aug 25, 600

Ernest who live from 1871 to 1937 designed an experiment to see if alpha particles, which were positive, would deflect as they passed through foil. He thought they would go straight through because of the plum pudding model. However some bounced back. The model was wrong! Ernest then found out the atom was empty space for electrons to move around and he claimed the positive charge was in the nucleus. His theory helped to explain the nucleus held the negative charge of the electrons.

James Chadwick

Aug 25, 620

James lived from 1891 to 1974. He is credited for finding that there were something else in the nucleus. The subatomic particle, the neutrons. This great subatomic particle (neutron) is neutral (no charge) and weighs around the same as the proton. He won the Nobel prize in 1935 for his neutron discovery.

Robert Millikan

Mar 2, 2022

There still was a piece of information missing, and that was the charge of the electron. Robert Millikin who was born in the year of 1868 and died in the year of 1953, figure this out. He did this with an oil drop, he determined the magnitude of the electron's charge was 1.602x10-19 coulombs . The charge was equal to -1 therefore the electron has a charge of -1.