History of Atom Timeline by Jannah Mar Bangha-On https://padlet.com/560049231/lw217mbxtusq en-us 2018-01-31 14:07:45 UTC 2025-12-15 13:11:54 UTC hello@padlet.com Democritus 560049231 https://padlet.com/560049231/lw217mbxtusq/wish/226560518 Year- 400 B.C.
Experiment- To find the atom, Democritus conducted a simple experiment that can still be done today. What he did was take a simple seashell and break it in half. He then took that half and broke it in half over and over and over and over again until he was finally left with a fine powder. He then took the smallest piece from the powder and tried to break that but could not. So that was how Democritus had discovered what he was the indivisible building block of life the atom.
What the scientist discovered- He discovered atoms.
Picture of their idea of the model of the atom-
]]> 2018-01-31 14:10:22 UTC https://padlet.com/560049231/lw217mbxtusq/wish/226560518 Bohr 560049231 https://padlet.com/560049231/lw217mbxtusq/wish/226565389 Year- 1913
Experiment- Electrons should move around the nucleus but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted. Bohr's theory could explain why atoms emitted light in fixed wavelengths.
What the scientist discovered- Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities.
Picture of their idea of the atom- ]]> 2018-01-31 14:18:50 UTC https://padlet.com/560049231/lw217mbxtusq/wish/226565389 Crookes 560049231 https://padlet.com/560049231/lw217mbxtusq/wish/226565437 Year- 1869-1875
Experiment- He experimented the Crookes  tube and and around 1869-1875 is where cathode rays, streams of electrons, were discovered.
What the scientist discovered- British chemist and physicist noted for his discovery of the element thallium and for his cathode-ray studies, fundamental in the development of atomic physics.
Picture of their idea of the atom- none]]> 2018-01-31 14:18:56 UTC https://padlet.com/560049231/lw217mbxtusq/wish/226565437 Thomson 560049231 https://padlet.com/560049231/lw217mbxtusq/wish/226565492 Year- 1897
Experiment- Thomson discovered the electron by experimenting with a Crookes, or cathode ray, tube. He demonstrated that cathode rays were negatively charged.
What the scientist discovered- Thomson had discovered the electron, a negatively charged part of every atom. Thomson held that atoms are uniform spheres of positively charged matter in which electrons are embedded.
Picture of their idea of the atom-]]> 2018-01-31 14:19:01 UTC https://padlet.com/560049231/lw217mbxtusq/wish/226565492 Rutherford 560049231 https://padlet.com/560049231/lw217mbxtusq/wish/226565647 Year- 1871-1937
Experiment- In 1911, Ernest Rutherford performed an experiment to test the plum pudding model. With this experiment, Rutherford discovered the nucleus.
What the scientist discovered- He discovered alpha and beta rays, set forth the laws of radioactive decay, and identified alpha particles as helium nuclei. Most important, he postulated the nuclear structure of the atom: experiments done in Rutherford’s laboratory showed that when alpha particles are fired into gas atoms, a few are violently deflected, which implies a dense, positively charged central region containing most of the atomic mass.
Picture of their idea of the atom-]]> 2018-01-31 14:19:14 UTC https://padlet.com/560049231/lw217mbxtusq/wish/226565647 Becquerel 560049231 https://padlet.com/560049231/lw217mbxtusq/wish/226565685 Year- 1896
Experiment- He exposed potassium uranyl sulfate to sunlight and then placed it on photographic plates wrapped in black paper, believing that the uranium absorbed the sun’s energy and then emitted it as x-rays.
What the scientist discovered- Radioactivity
Picture of their idea of the atom-  none
Scientist
]]> 2018-01-31 14:19:18 UTC https://padlet.com/560049231/lw217mbxtusq/wish/226565685 Chadwick 560049231 https://padlet.com/560049231/lw217mbxtusq/wish/226565781 Year- 1935
Experiment- 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.
In the path of the rays, Chadwick put a target. When the rays hit the target, they knocked atoms out of it. The atoms, which became electrically charged in the collision, flew into a detector. That's when he discovered the neutron.

What the scientist discovered- Neutron
Picture of their idea of the atom-
]]> 2018-01-31 14:19:27 UTC https://padlet.com/560049231/lw217mbxtusq/wish/226565781 Dalton 560049231 https://padlet.com/560049231/lw217mbxtusq/wish/226715744 Year- 1803
Experiment- He experimented with gases and that led him to the theory of atoms.
What the scientist discovered- He proposed the modern theory of atoms.
Picture of their idea of the atom- ]]> 2018-01-31 18:07:39 UTC https://padlet.com/560049231/lw217mbxtusq/wish/226715744 560049231 https://padlet.com/560049231/lw217mbxtusq/wish/227038368 2018-02-01 14:09:58 UTC https://padlet.com/560049231/lw217mbxtusq/wish/227038368 560049231 https://padlet.com/560049231/lw217mbxtusq/wish/227039174 2018-02-01 14:11:15 UTC https://padlet.com/560049231/lw217mbxtusq/wish/227039174 Current accepted atom model 560049231 https://padlet.com/560049231/lw217mbxtusq/wish/227193301 Bohr Model discovered by Niels Bohr ]]> 2018-02-01 18:11:06 UTC https://padlet.com/560049231/lw217mbxtusq/wish/227193301