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460 BCE
Democritus
Everything is composed of "atoms", which are physically, but not geometrically, indivisible. Between atoms, there lies empty space. Atoms are indestructible. Atoms have always been, and always will be, in motion. There are an infinite number of atoms, and kinds of atoms, which differ in shape and size. -
Antoine Lavoisier
He used his experiment that turned HgO into Hg+O, using this he came up with the Law of Conservation, which states that matter cannot be created nor destroyed -
John Dalton
All matter is made of atoms. Atoms are indivisible and indestructible. All atoms of a given element are identical in mass and properties. Compounds are formed by a combination of two or more different kinds of atoms. A chemical reaction is a rearrangement of atoms. -
J.J. Thomson
Thomson realized that the accepted atomic model did not account for negatively or positively charged particles. Therefore, he proposed a model of the atom in which he played off of plum pudding, where the negatively charged atoms were represented by the raisins and the dough contained the positively charged particles. Although his atomic model did explain some of the electrical properties of the atom due to the electrons, but failed to recognize the positive charges in the atom as particles. -
Max Planck
Planck was able to deduce the relationship between the energy and the frequency of radiation. In a paper published in 1900, he announced his derivation of the relationship: this was based on the revolutionary idea that the energy emitted by a resonator could only take on discrete values or quanta. The energy for a resonator of frequency v is hv where h is a universal constant, now called Planck's constant. -
Marie Curie
She began the systematic study of other elements to see if there were others that also emitted this strange energy. She discovered that thorium also emitted radiation, and further, that the amount of radiation depended upon the amount of element present in the compound. She deduced that radioactivity does not depend on how atoms are arranged into molecules, but rather that it originates within the atoms themselves. -
Robert Millikan
Millikan discovered accurately both the charge,and by virtue of the charge-to-mass ratio, the mass of the electron. -
Ernest Rutherford
Rutherford was the first to discover that atoms have a small charged nucleus surrounded by largely empty space, and are circled by tiny electrons. He is also credited with the discovery of the proton in 1919, and hypothesized the existence of the neutron. Known for his Rutherford Model. -
Albert Einstein
The quantum theory of light. Einstein proposed that light is composed of separate packets of energy, called -- quanta or photons -- that have some properties of particles and some properties of waves. He also explained the photoelectric effect, which is the emission of electrons from some solids when they're struck by light. Television is a practical application of Einstein's theory of light. -
Niels Bohr
"Bohr's greatest contribution to modern physics was the atomic model. The Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons.
Bohr was the first to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element.
The chemical element bohrium (Bh), No. 107 on the periodic table of elements, is named for him" -
Erwin Schrodinger
Erwin Schrödinger took the Bohr atom model one step further. Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. The quantum mechanical model predicts the odds of the location of the electron. The probability of finding the electron is greatest, and conversely, the electron is less likely to be in a less dense area of the cloud. This model introduced the concept of sub-energy levels -
James Chadwick
He discovered the neutron in atoms, which are located in the center of an atom, they have neither positive nor negative charge but contribute to the atomic weight with the same effect as a proton. -
Louis De Broglie
De Broglie developed his revolutionary theory of electron waves, which he had published earlier in scientific journals. The notion that matter on the atomic scale might have the properties of a wave was rooted in a proposal Einstein had made 20 years before. . The dual nature of light, however, was just beginning to gain scientific acceptance when de Broglie extended the idea of such a duality to matter -
Werner Heisenberg
In 1925, Werner Heisenberg formulated a type of quantum mechanics based on matrices. In 1927 he proposed the "uncertainty relation", setting limits for how precisely the position and velocity of a particle can be simultaneously determined
