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800 BCE
The Alchemists
One of the leading ideas of medieval Arabic alchemy was the theory that all metals were formed of sulfur and mercury in various proportions and that altering those proportions could transform the metal under study—even to produce silver or gold from lead or iron. -
400 BCE
Democritus
The Greek philosopher Democritus introduced the idea of the atom as the basic building block matter. -
384 BCE
Aristotle
Aristotle was one of the greatest philosophers who ever lived and the first genuine scientist in history. He made pioneering contributions to all fields of philosophy and science, he invented the field of formal logic, and he identified the various scientific disciplines and explored their relationships to each other. -
300 BCE
Plato
Plato was a philosopher during the 5th century. He found that there are only five solid shapes whose sides are made from regular polygons for example, the cube. Plato was so impressed with this discovery that he was convinced that atoms of matter must derive from these five fundamental solids. -
Robert Boyle
Robert Boyle discovered that the volume of a gas decreases with increasing pressure and vice versa. This became Boyle's law. A leading scientist and intellectual of his day, he was a great proponent of the experimental method. -
Lavoisier
In 1789, Lavoisier discovered that mass is neither created nor destroyed in chemical reactions. In other words, the mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction. -
John Dalton
John Dalton experimented on glasses, and these experiments led to his discovery that total pressure of a mixture or glass amounted to the sum of partial pressures that each individual gas exerted while occupying the same space. In 1803 this scientific principle officially came to be known as Dalton's Law of Partial Pressures. -
Dmitri Mendeleev
Russian chemist Dmitri Mendeleev jotted down the symbols for the chemical elements, putting them in order according to their atomic weights and inventing the periodic table. It was perhaps the greatest breakthrough in the history of chemistry. -
J.J. Thomson
On April 30, 1897, British physicist J.J. Thomson announced his discovery that atoms were made up of smaller components. This finding revolutionized the way scientists thought about the atom and had major ramifications for the field of physics. -
Planck's Quantum Theory of Light
In the year 1900, Planck postulated that the energy of light is proportional to the frequency, and the constant that relates them is known as Planck's constant. His work led to Albert Einstein determining that light exists in discrete quanta of energy, or photons. -
The Curies
The Curie family is a French family with a number of illustrious scientists. Marie and Pierre Curie successfully isolate radioactive radium salts from the mineral pitchblende in their laboratory in Paris. In 1898, the Curies discovered the existence of the elements radium and polonium in their research of pitchblende. -
Albert Einstein
In 1905, Einstein proved the existence of atoms, and revolutionized all science through the use of statistics and probability. Atomic theory says that any liquid is made up of molecules. These molecules are always in random, ceaseless motion. -
Photoelectric Effect
Discovered by Albert Einstein, the Photoelectric effect is the phenomenon of emission of electrons from the surface of metals when light or any other radiation of suitable frequency falls on the metal. The number of photoelectrons emitted is directly proportional to the intensity of the light incident for a given metal and frequency of the light. -
Ernest Rutherford
Ernest Rutherford is known for his pioneering studies of radioactivity and the atom. He discovered that there are two types of radiation, alpha and beta particles, coming from uranium. He found that the atom consists mostly of empty space, with its mass concentrated in a central positively charged nucleus. -
Robert Millikan
Millikan's earliest major success was the accurate determination of the charge carried by an electron, using the elegant “falling-drop method”; he also proved that this quantity was a constant for all electrons, thus demonstrating the atomic structure of electricity. -
Henry G. J. Mosely
In 1913, while working at the University of Manchester, he observed and measured the X-ray spectra of various chemical elements using diffraction in crystals. Through this, he discovered a systematic relation between wave- length and atomic number. This discovery is now known as Moseley's Law. -
Niels Bohr
Niels Bohr proposed a model of the atom in which the electron was able to occupy only certain orbits around the nucleus. This atomic model was the first to use quantum theory, in that the electrons were limited to specific orbits around the nucleus. -
Schrodinger Equation
Discovered by Erwin Schrodinger in 1926, The Schrodinger equation gives us a detailed account of the form of the wave functions or probability waves that control the motion of some smaller particles. -
Werner Heisenberg
Werner Heisenberg contributed to atomic theory through formulating quantum mechanics in terms of matrices and in discovering the uncertainty principle, which states that a particle's position and momentum cannot both be known exactly. -
James Chadwick
In 1932, Chadwick made a fundamental discovery in the domain of nuclear science. He proved the existence of neutrons, and elementary particles devoid of any electrical charge.
