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350 BCE
Democritus
c. 350 BC, the theory of Democritus held that everything is composed of "atoms," which are physically, but not geometrically, indivisible; that between atoms, there lies empty space; that atoms are indestructible, and have always been and always will be in motion; that there is an infinite number of atoms and of kinds of atoms, which differ in shape and size. -
Antoine Lovoisier
In 1789 Lovoisier found that the total mass of products & reactants in a chemical reaction is always the same. This led to the theory of law of conservation of mass. The was a crucial breakthrough in the work of atomists in confirming what matter was made of as it was proved that atoms are not created or destroyed when a reaction happens. -
John Dalton
In 1803 Dalton discovered that oxygen combined with 1-2 volumes of nitric oxide in closed vessels over water, this pioneered observation of integral multiple proportions provided important experimental evidence for his incipient atomic ideas. -
Joseph Louis Proust
In 1806, Proust summarized his observations into what is now called Proust’s law. It stated that chemical compounds are formed by constant and defined ratios of elements, as determined by mass. For example, carbon dioxide Is composed of 1 carbon atom and 2 oxygen atoms. Therefore, by mass, carbon dioxide can be described by the fixed ratio of 12 (mass of carbon), 32 (mass of oxygen) or simplified as 3:8. -
John Dalton
In 1808 Dalton published his first general account of chemical atomic theory. This is now a cornerstone of modern chemistry. -
Micheal Faraday
Faraday is most famous for his contributions to the understanding of electricity and electrochemistry. In this work he was driven by his belief in the uniformity of nature and the interconvertibility of various forces, which he conceived early on as fields of force. In 1821 he succeeded in producing mechanical motion by means of a permanent magnet and an electric current—an ancestor of the electric motor. -
Michael Faraday
In 1831, Micheal Faraday converted magnetic force into electrical force, thus inventing the world’s first electrical generator. -
Robert Millikan
In the 1890’s Millikan had theorized that electricity was conveyed by a minuscule unit, the electron. Thus starting his research on the electron. -
Henri Becquerel
Like Thomson’s discovery of the electron, the French physicist, Henri Becquerel made the discovery of radioactivity in uranium. This radically changed the ideas of the chemists and physicists about atomic structures. Radioactivity demonstrated that the atom was neither indivisible nor immutable. -
JJ Thompson
Thomson’s experiments in 1897 with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles, otherwise now known as electrons. -
Marie & Pierre Curie pt.1
M. Curie conducted her own experiments on uranium rays and discovered that they remained constant, no matter the condition or form of the uranium. The rays, she theorized, came from the element's atomic structure. This revolutionary idea created the field of atomic physics. Curie herself coined the word "radioactivity" to describe the phenomena.. -
Marie & Pierre Curie pt.2
Following Curie’s discovery of radioactivity, she continued her research with her husband Pierre. Working with the mineral pitchblende, the pair discovered a new radioactive element in 1898. They named the element polonium, after Curie's native country of Poland. They also detected the presence of another radioactive material in the pitchblende and called that radium -
Ernest Rutherford
Ernest Rutherford - Ernest Rutherford is known for his pioneering studies of radioactivity and the atom. In 1899, he discovered that there are two types of radiation, alpha and beta particles, coming from uranium. -
Max Planck
Planck made many contributions to theoretical physics, but his fame rests primarily on his role as originator of quantum theory. This theory revolutionized our understanding of atomic and subatomic processes, just as Albert Einstein’s theory of relativity revolutionized our understanding of space and time. He discovered the quantum of action, now known as Planck's constant, h, in 1900. -
Marie and Pierre Currie
In 1902, the Curies announced that they had produced a decigram of pure radium, demonstrating its existence as a unique chemical element. -
Albert Einstein
In 1905, Einstein explained the equivalency of mass and energy, expressed by the famous equation e=mc2. Einstein also in 1905 mathematically proved the existence of atoms, and thus helped revolutionize all the sciences through the use of statistics and probability. -
Robert Millikan
In 1910 Robert Millikan determined the magnitude of the electrons charge. He did this by measuring how various drops of oil moved, Millikan showed that their charge always was a multiple of a precisely determined charge (the charge of an electron) -
Ernest Rutherford
In 1911, he found that the atom consists mostly of empty space, with its mass concentrated in a central positively charged nucleus. -
Niels Bohr
In 1913, Niels Bohr, proposed a theory for the hydrogen atom, based on quantum theory that some physical quantities only thank discrete values. Electrons move around a nucleus, but only in prescribed orbits, and if electrons jump to a lower-energy orbit, the difference is sent out as radiation. -
James Chadwick
Chadwick is best known for his discovery of the neutron in 1932. Chadwick's findings were pivotal to the discovery of nuclear fission, and ultimately the development of the atomic bomb. -
Murray Gell-Mann
In the 1960s Gell-Mann developed a method to categorize the huge number of particles that were being created at particle accelerators worldwide. Gell-Mann’s model also predicted the existence of another fundamental type of particle that makes up particles including protons and neutrons. Gell-Mann dubbed them “quarks” and they were later discovered experimentally at the Stanford Linear Accelerator Center (SLAC) in the US.