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460 BCE
Atom First Proposed
Born on 460 BC in Abdera, Thrace; Democritus is a philosopher who expands upon the atomic theory of Leucippus by proposing the idea that all matter is made up of tiny indestructible objects that have been and always will be moving forever. They are invisible physically but not geometrically, and between them is merely empty space. These atoms have infinitely many different kinds of atoms in many different shapes and sizes. -
Modern Atomic Theory
John Dalton, born on September 6, 1766, in Eaglesfield, England; founded the idea that all matter is made up tiny indestructible particles by experimenting with gases (the first evidence-based theory). He also discovered that all atoms of an element are identical and atoms of different elements have different weights and chemical properties. It is also stated that atoms cannot be created nor destroyed. -
Subatomic Particles & Thompson Model
J.J Thompson, born on December 18, 1856, in Cheetham Hill, England, Thompson performs the Cathode ray tube experiment in 1897. He concludes that all atoms are made up of the same particles. He also discovered that the rays was less mass than a hydrogen atom; therefore discovering subatomic particles, to which he called "corpuscles" (now called electrons). He is also responsible for creating the Thompson atomic model. -
Cathode Ray Tube Experiment
The Cathode Ray Tube experiment was performed by J.J. Thompson. It was done by sending cathode rays through a vacuum and measuring their deflection and mass. The mass of the rays was discovered as much less than a single hydrogen atom, which means that atoms are made up of subatomic (smaller) particles. -
Nucleus & Rutherford Model
Ernest Rutherford, born on August 30, 1871, in Spring Grove, Zealand; He performs the Gold Foil Experiment in 1908, in which he shot a beam of alpha particles at a thin sheet of gold foil and found that some particles were deflected. Because of this, he concluded that the nucleus of the atom was causing it. He also is responsible for the Rutherford model of the atom. -
Gold Foil Experiment
Performed by Ernest Rutherford, the Gold Foil experiment is done by shooting alpha particles towards gold foil through a slit. Some rays reflected off the foil, while some went through. This was because of some of the particles were deleting off of the nucleus of the atoms in the foil. -
Charge of Electrons
Robert Milikan, born on March 22, 1868, in Morrison, Il. He worked on experiments to determine the electric charge of electrons. In 1909, he performed the Oil Drop experiment in to determine that charge of the particles. Their charge was found to be negative. -
Oil Drop Experiment
The Oil Drop Experiment was done by Robert Milikin. It entailed observing the electrical charge of 2 oil droplets between two parallel metal plates, forming a capacitor. The droplets were ionized, making them negative. AN electric charge was introduced to the plates until the droplets reached mechanical equilibrium. The charge can now be determined. -
Bohr Model
Neils Bohr was born on October 7, 1885, in Copenhagen, Denmark. He created the Bohr Model of the atom in 1913, where he described that the energy levels of electrons are discrete and that electrons revolve around the atomic nucleus but can switch from one energy level to another. -
Electron Cloud Model
Erwin Schrödinger was born on August 12, 1887, in Vienna, Austria. In 1926, he developed an Electron Cloud Model, which consisted of a dense nucleus surrounded by a cloud of electrons at various levels. He determined regions at which electrons would be found using mathematics. He used mathematical equations to describe the likelihood of finding electrons in a specific position. This leads to scientists today being able to examine groups of atoms and view a single atom with a microscope. -
Neutron Discovered
James Chadwick was born on October 20, 1891, in Bollington, United Kingdom. Chadwick discovered the Neutron through a number of the new radiation consisted of particles. These particles are now known as Neutrons. He discovered the neutron in 1932, between WW1 and WW2, while living in Manchester, New England. His discovery leads to the creation of the atomic bomb, which he helps make.
