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Democritus
born at Abdera, about 460 BCE, co originated that all matter is composed of indivisible elements, Everything is composed of “atoms”, which are physically, but not geometrically, indivisible -
John Dalton
Created Dalton's Law, it stated that pressure of a mixture of gases is the sum of the contributions of the individual components of the mixture. Experiments with gases that first became possible at the turn of the nineteenth century led John Dalton to propose a modern theory of the atom that states that matter is made up of atoms that are indivisible and indestructible; all atoms of an element are identical atoms of different elements have different weights and different chemical properties -
JJ Thomson
He discovered the electron by experimenting with a Crookes, or cathode ray, tube. He demonstrated that cathode rays were negatively charged. In addition, he also studied positively charged particles in neon gas. He was awarded the Nobel Prize in Physics in 1906 for the discovery of the electron and his work on the electrical conductivity of gases -
Robert Millikan
He discovered the value for electron charge, through the famous oil-drop experiment. He was the first to receive a Ph.D. from the physics department at Columbia University. He went on to win the Nobel Prize for physics for his work on the photoelectric effect and measuring the charge of the electron. -
Ernest Rutherford
Rutherford overturned Thomson's model in 1911 with his well-known gold foil experiment in which he demonstrated that the atom has a tiny and heavy nucleus. Rutherford designed an experiment to use the alpha particles emitted by a radioactive element as probes to the unseen world of atomic structure. If Thomson was correct, the beam would go straight through the gold foil. Most of the beams went through the foil, but a few were deflected. -
Neils Bohr
Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well-defined quantities. Electrons should move around the nucleus but only in prescribed orbits. Bohr's theory could explain why atoms emitted light in fixed wavelengths. He received the Nobel Prize in Physics in 1922 -
Erwin Schrodinger
Schrodinger used mathematical principles in order to describe how to find an electron at a certain position within the atom. He proposed the wave equation of electrons and took the atomic model one step further than Bohr. Schrodinger created the quantum mechanical model of the atom. Different from Bohr’s model, this atom model does not define the path of an electron but instead offers a prediction of the approximate location an electron will be at next. -
James Chadwick
Chadwick graduated from the Honours School of physics in 1911 and spent the next two years of his life working on various radioactivity problems. In 1932 by bombarding beryllium atoms with alpha particles and finding that unknown radiation was produced, he proved the existence of neutrons. Chadwick experimented with atomic disintegration and later this would lead to the creation of atomic bombs. Through Chadwick’s discovery, the adequate model of the atom also became available to chemists.
