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460 BCE
Democritus (460 B.C- 370 B.C)
One of the first people to suggest that atoms were real. He explained that atoms were invisible and indestructible. People questioned him because he didn't use scientific method to figure this out. -
John Dalton (1766-1844)
Dalton used experimental methods and turned Democritus' work on atoms into scientific theory. What he came up with is called "Daltons Atomic Theory." This has four stages, stage 1, everything is made up of atoms. Stage 2, atoms from the same element are identical, different elements have different atoms. 3, different atoms can come together to form a compound. 4 Chemical reactions occur when atoms are separated from each other, joined, or rearranged in a different combination. -
Eugen Goldstein (1850-1930)
The start of protons begins with Eugen. He observed a cathode-ray tube and found rays traveling in the direction opposite to that of the cathode rays. He called these rays canal rays and concluded that they were composed of positive particles. These positive particles were named protons. -
J.J Tomson (1856-1940)
Electrons. Thomson performed experiments that involved passing electric current through gases at low pressure. He sealed the gases in glass tubes fitted at both ends with metal disks called electrodes. The electrodes were connected to a source of electricity. ne electrode, the anode, became positively charged. The other electrode, the cathode, became negatively charged. Doing more experiments and research J.J comes to the conclusion that there is negatively charged particles. -
Ernest Rutherford (1871-1937)
Ernest and his co-workers made the god-foil experiment. They used helium with a loss of two electrons and a double positive charge. This was a beam directed at gold foil. A lot of these particles went through the foil and some bounced back. He concluded that all the positive charge and almost all the mass are concentrated in a small region that has enough positive charge to account for the great deflection of some of the alpha particles. He called this region the nucleus. -
Robert A Milikan (1868-1953)
Robert set out to find the quantity of an electrons charge. He did an oil drop experiment in which he suspended negatively charged oil droplets between two charged plates. He then changed the voltage on the plates to see how this affected the droplets’ rate of fall. Robert found that each drop was a multiple of 1.60x10^19. Thus this was the quantity of the charge. -
James Chadwick (1891-1794)
Chadwick confirmed the Neutrons. "Chadwick put a piece of beryllium in a vacuum chamber with some polonium. The polonium emitted alpha rays, which struck the beryllium. When struck, the beryllium emitted the mysterious neutral rays." -google