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460 BCE
Democritus
Democritus was an ancient Greek philosopher who is most remembered for his theory of atoms. He thought everything was composed of "atoms" and they were both indestructible and indivisible. He also said atoms are always moving and between atoms lies empty space. -
John Dalton
John Dalton was a English chemist, physicist and meteorologist. He is best known for introducing the atomic theory to chemistry. He also developed methods to calculate atomic weights and structures to formulate the law of partial pressures. He said all matter is made of atoms and atoms are given an element that is identical is mass and properties. -
Dmitri Mendeleev
Dmitri was a Russian chemist who is mostly known as the creator of the first periodic table. He discovered that when known chemical elements were arranged in order of increasing atomic weight, his table created a pattern. He published over 400 books and articles sharing his findings with the world. -
Eugene Goldstein
Eugene was a German physicist who is credited with the discovery the proton, and said that it has an opposite and equal charge as an electron. He also worked on electrical phenomena in gases with cathode and canal rays. -
J.J Thomson
J.J Thomson's experiment using a cathode ray tube proved that atoms have negatively charged particles inside them, which he called electrons. He said there was negatively charged electrons inside positively charged "soup", The electron was considered the first subatomic particle. -
Robert Millikan
Robert Millikan used the electron and created the oil drop experiment. This experiment helped quantify the charge of an electron, and discover that all of the oil drops had charges that were simple multiplies of a single number. Millikan established the charge on an electron. -
Ernest Rutherford
Rutherford created the gold-foil experiment where he discovered that the nuclear structure of the atom consisted of small, positively charged nucleus, with negatively charged electrons a great distance away from the nucleus. He also discovered alpha and beta rays and the idea of radioactive decay. Rutherford's model replaced Thomson's model at the time. -
Niels Bohr
Bohr was the first to discover that electrons travel in separate orbits around the nucleus. He proved that the number of electrons in the outer orbit also determines the properties of that element. Bohr modified the Rutherford model by forcing the electrons to move in orbits of both fixed size and energy, he did this using the shell model. -
James Chadwick
Chadwick proved that neutrons exist and that they are elementary particles that devoid from any electric charge. He found that certain elements could release energy when mixed with other kinds of particles. This gave him the idea that a tiny particle inside the nucleus of all atoms was a neutron.
