Timeline on the History of the Atom

John Dalton ( a chemist ) proved Democritus’ ideas through multiple series of tests and experiments. One of them included finding the pressure of gas. He concluded that glasses must contain particles that are always in motion. He stated that elements made up of these particles can combine in endless ways. This shaped the idea of what an atom was.

JJ Thomson was a English physicist and Nobel Laureate in Physics. He discovered the atom. Thomson’s model predicted that electrons and protons were evenly distributed throughout an atom . He then proposed an atomic model known as the “plum pudding” model. He also made an advanced discovery of electrons. He passed an electric current through a vacuum tube.

In the 1910’s Ernest Rutherford wasn't convinced by the model of the atom by Thomson so he created his famous Gold Foil Experiment. He fired alpha particles on a gold foil and measured the deflection as the particles came out the other side. Most of the particles didn’t deflect at all, and every now and then a particle would deflect all the way back, so he said there was a positive center of the foil and called it the nucleus. With his discovery Rutherford stated the atom was like a mini solar system and that electrons orbited the nucleus in a wide orbit. Ernest Rutherford was one of JJ Thomson’s students. He discovered the positively charged nucleus by probing atoms of gold foil with positively charged (alpha) particles. He then discovered the proton.

Niel Bohr used his knowledge of energy and quantum physics to perfect Rutherford's model. He was able to answer why electrons don't collapse into the nucleus. His model is called “The Rutherford- Bohr Model”. There was a problem with his theory though which was that electrons did not travel on a specific path.

Erwin Schrödinger is an Australian physicist that took the Bohr atom model a step further. Erwin used the Heisenberg uncertainty principle to come up with his own atomic model. He used mathematical equations to describe the likelihood of finding an electron in a certain positions. This model is known as the Quantum Mechanical model of the atom. The Quantum model doesn’t define the exact path of an electron, but predicting the odds of the location of the electron.

James Chadwick discovered the neutron. His discovery explained why the mass of an atom could not be attributed entirely to the mass of protons. Also, his discovery directly led to the development of the atomic bombs used in World War II. He stated that neutrons are located in the center of an atom in the nucleus along with protons. They have neither a positive or negative charge but contribute the atomic weight. With the same effect as a proton.

Timeline on the History of the Atom

450-500 BC Democritus

1890-1898 JJ Thomson

1932 James Chadwick

1913 Niels Bohr

Democritus was a Greek Philosopher. He was the first person to discover the theory of the atom. “The theory of the Universe” Democritus had an idea of what would happen if he were to cut a piece of matter into smaller pieces. He cut an apple so small that it could not be cut any further. He called these small bits “Atomos”. The greek word atomos means “indivisible”. He was the first to develop the idea that matter is made of particles called atoms.

450-500 B.C

1890-1898

1914

1932

1800-1808

1910

1920

1910 Ernest Rutherford

1800-1803 John Dalton

1920 Erwin Schrödinger