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Democritus - 400BC, Ancient Greek pre-Socratic Philosopher
Democritus suggested that all materials in the world are made of atoms. He said that atoms were different shapes and they were arranged or positioned near each other. He also said that when we taste or feel something, it is a result of the atoms of the substance to the atoms in our sense organs. Democritus's theory also suggested a basis explanation for the changes that occur when matter chemically transforms. -
Robert Boyle - 1661, Anglo-Irish Natural Philosopher, Chemist, Physicist, and Inventor
Boyle was the first scientist to conduct controlled experiments. Boyle discovered the inverse relationship that as volume of gas decreases, the pressure of the gas increases (and vice versa), and this relationship became known as Boyle's Law. Boyle was the first to conduct litmus tests (to tell acids from bases), and he also introduced many other standard chemical tests. Boyle defined what an element was and how it cannot be broken down into more simple forms (compound can be broken down). -
Antoine Lavoisier - 1775, French Chemist, "Father of Modern Chemistry"
One thing that Lavoisier did was prove the phlogiston theory (when things burn they release phlogiston into the air) to be wrong. Another thing Lavoisier did was develop the Law of Conservation of Mass which states that in a chemical reaction no mass is ever lost. He also invented a system of naming chemical compounds. He came up with the name for Hydrogen. He disproved the theory that water was an element but rather a compound of Hydrogen and Oxygen. Lavoisier also made a chemistry textbook. -
John Dalton - 1803, English Chemist, Meteorologist, and Physicist
Dalton was the first to describe the atom as an important chemical object. He came up with a theory about atoms which is known as Dalton's Atomic Theory. Dalton's theory had four parts: 1.) All matter is made of atoms, and atoms are invisible and indestructible. 2.) All atoms of a given element are identical in mass and properties. 3.) Compounds are formed by a combination of two or more different kinds of atoms. 4.) A chemical reaction is a rearrangement of atoms. -
Dmitri Mendeleev - 1869, Russian Chemist and Inventor
Mendeleev put elements into seven groups that had similar properties and this became the first periodic table. Mendeleev's periodic table was organized by the increasing atomic weights. Mendeleev also came up with the Periodic Law because, he discovered that the properties of elements were periodic functions of their atomic weights. Mendeleev left gaps in his periodic table for elements that were not discovered yet. -
Eugen Goldstein - 1886, German Physicist
Goldstein discoved the proton by the Canal Rays (Goldstein took the cathode ray tube and put holes in it to create the Canal Rays). Creating the Canal Rays led to the discovery of the proton because, positive and negative charged protons collided in the cathode ray tube (each created a different color in different locations on the tube). -
J.J. Thomson - 1897, English Physicist
The most important discovery Thomson made was the electron. Thomson identified the electron and classified it as a subatomic particle. To find the electron, Thomson conducted experiments that showed that cathode rays were altered by magnetic and electric fields. Thomson used an apparatus to show how a beam of electrons can come across other magnetic and electric fields, and the electrons can be adjusted until both of their effects become balanced. Came up with the plum pudding model of the atom. -
Max Planck - 1900, German Theoretical Physicist
Planck developed the quantum theory which lead to a greater understanding of the atomic and subatomic processes. The quantum theory stated that energy did not flow in a steady process but was delivered in packets or groups. As temperature increases, the wavelength of radiation changes from orange, to yellow, to blue. Energy was in the packets and as it got hotter the colors changed (thermodynamics). Planck's study of thermodynamics lead to the quantum theory. -
Robert Millikan - 1909, American Experimental Physicist
Millikan measured the charge of an electron by conducting an experiment with his oil-drop apparatus. With Millikan's experiment, he was able to show that charges on an oil droplet were always a multiple of a small, definite value. Millikan then was able to prove Thomson's hypothesis correct. Millikan discovered that the mass of an electron is at least 1000 times smaller than the lightest atom. His experiment measured the charge (1.602x10-19 coulomb) and mass (9.11x10-28 gram) of the electron. -
Ernest Rutherford - 1898, 1911, British Physicist, "Father of Nuclear Physics", Discovered a Nuclear Atom
In 1898, Rutherford studied the radiations given off from the elements Uranium and Thorium and named them alpha and beta. In 1911, Rutherford's gold-foil experiment showed that when alpha particles are "shot" into gas atoms, some ricochet violently. This suggested that a dense, center region that was positively charged contained most of the atomic weight. Rutherford suggested that most of the atom's volume was empty space occupied by electrons. Rutherford found evidence of protons and neutrons. -
Henry Moseley - 1913, English Physicist
Moseley conducted experiments using X-ray crystallography and he found out that the energy given off by the elements, that tested successfully, increased in a continuous order. Moseley suggested that this relationship was a function of the positive charge on the nucleus. This relationship rearranged the periodic table by using atomic numbers instead of atomic weights (Mendeleev suggested) to represent the progression of the elements. Also discovered many missing elements and new table left room. -
Niels Bohr - 1922, Danish Physicist
Bohr came up with an atomic model: atom is small, the nucleus is positively charged, and electrons orbit the nucleus. Also was the first to discover that the electrons travel on seperate orbits around the nucleus. Also discovered that the properties of an element are determined by the number of electrons in the outer orbit. Came up with the liquid droplet theory that accurately represented an atom's nucleus. Formed the concept that an electron can be a particle or wave (based on quantum theory). -
Erwin Schrodinger - 1926, Austrian Physicist
Schrodinger used Bohr's atomic model but instead using mathematical equations to describe the possibility of finding an electron in a certain area, which was known as the quantum mechanical model of the atom. This quantum mechanical model does not tell the exact position of the electron, but rather predicts the position. This model is a nucleus surrounded by an electron cloud, and as the electron cloud becomes more dense, finding the electron is easier. This model introduced sub-energry levels. -
James Chadwick - 1932, English Physicist, Discovered the Neutron
Chadwick believed that there was some type of neutral particles that have no charge inside of the nucleus. Chadwick conducted many experiments to try to prove his beliefs correct, but he failed. Chadwick used what he knew about other scientists' experiments on the same issue to conduct his own experiment using wax. His experiment showed how the protons acted with the wax, and the protons acted the same way as if they were hit by electrically neutral particles (with the same mass as the protons).
