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John Dalton
He was an English chemist. He proposed the "Atomic Theory" and that atoms were tiny, solid spheres. -
Amadeo Avogadro
proposed what is now known as Avogadro's Hypothesis.. The hypothesis states that at the same temperature and pressure, equal volumes of gases contain the same number of molecules or atoms. -
Joseph Thomson
He found the electron and said that the nucleus has electrons embedded in it to give charge. He also invented the cookie dough model. -
Dimitri Mendeleev
He arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law. -
William Crookes
Discovered cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass. -
George Johnstone Stoney
Proposed that electricity was made of discrete negative particles he called electrons ". -
Marie and Pierre Curie
They discovered radium, an element that disintegrated into other elements. This proved that the atoms of one element at least were not indivisible. -
Federick Soddy
Observed spontaneous disintegration of radioactive elements into variants he called "isotopes" or totally new elements, discovered "half-life", made initial calculations on energy released during decay. -
Robert Millikan
He determined the unit charge of the electron with his oil drop experiment. Thus allowing for the calculation of the mass of the electron and the positively charged atoms. -
Ernest Ruthford
He proposed that atoms are mostly empty space and that positively charged nucleus electrons surrounded nucleus. -
Henry Moseley
He wrote"The atomic number of an element is equal to the number of protons in the nucleus" which was used to reorganize the periodic table based upon atomic number instead of atomic mass. -
Francis Aston
He invented the mass spectrograph . He was the first person to observe isotopes. For example he observed that there were three different kinds of hydrogen atoms -
Niels Bohr
He improved that explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons. -
Louis de Broglie
He discovered that electrons had a dual nature-similar to both particles and waves. Particle/wave duality. Supported Einstein. -
Erwin Schroedinger
He developed a mathematical description of electrons (Quantum Mechanical Model). -
Werner Heisenberg
Described atoms by means of formula connected to the frequencies of spectral lines. Proposed Principle of Indeterminancy - you can not know both the position and velocity of a particle. -
James Chadwick
He discovered the neutrons. -
Murray Gell-Mann
He was noted for his classification of subatomic particles and his proposal of the existence of quarks. -
Aristole
He believed in the four elements of air, earth, water and fire. Aristotle felt that regardless of the number of times you cut a form of matter in half, there will always be a smaller piece of that matter. -
Democritus
Democritus was a Greek philosopher in 400 B.C. He believed that all substances were made up of atoms.
