States that water is the simplest substance on Earth
Anaxgoras and Empedocles
Changes in matter are due to changes in indivisible particles
Separated indivisible matter into four elements; earth, water, fire and air.
Matter is made of small indivisible particles which have different form, position and arrangement. Democritus named these particles atoms.
Gathered all theories up to date and was responsible for formalizing the knowledge into one idea. Aristotle was leery that Democritus’s atoms didn’t account for the great variance of matter.
Taught that in order to understand the natural universe there must first be observation, allowing for evidence to come from the natural world.
The universe is a mechanical universe with small solid masses in constant motion
Developed an atomic theory stating that spherical atoms had measurable properties of mass
Split molecules with electricity by means of electrolysis, developed laws of electrolysis
Built the first cathode ray tube, used for gas discharge
James Clerk Maxwell
Magnetic and electric fields filled “empty” space in atoms
Sir William Crookes
Studied the properties of cathode rays and found that they exhibit negative charge and mass.
E. Goldstein<> Used cathode ray tubes to discover that “canal rays” have opposite properties of electron.
Used cathode ray tubes to observe that nearby chemicals glowed and the penetrating rays coming from the cathode ray tube were not affected by magnetic fields. He named these rays, X-Rays.
Discovered that some chemicals spontaneously decompose and give off penetrating rays while working with X-rays and photography paper.
Discovers the electron and used cathode ray tubes to determine the charge to mass ratio of an electron to be 1.759 x 108 Coulombs/gram.
Found canal rays were associated with a proton, H+.
Marie Skodowska Curie
Named the spontaneous decay process of uranium and thorium to be radioactivity.
Discovers alpha and beta rays emitting from radium.
Discovered that radioactive elements have isotopes, and half lives. Made preliminary calculations concerning the energy released during decay.
Used quanta, discrete units of energy to explain glowing hot matter.
While working on radioactive substances, Curie discovers gamma rays.
Saturnian model of the atom where there is flat rings of electrons revolving around a positively charged particle.
Inert gases have stable electron configurations.
Discovers alpha rays are heavily positively charged particles.
Publishes theory on special relativity and states that matter can be converted into energy.
Used an electrical device to click when hit with an alpha particle.
Performed an oil drop experiment to determine the charge and the mass of an electron to be 1.602 x 10-19 C and 9.11 x 10-28 g respectively.
Performed the gold foil experiment to determine that the nucleus is a small, dense, and positively charged part of the atom, based on the assumption that electrons are on the outside of the nucleus. Develops the plum pudding model of the atom.
Publishes paper regarding combining nuclear and quantum theories.
Determined the charge of the nuclei of most atoms using X-ray tubes. Stated that the atomic number is equal to the number of protons in the nucleus.
Used mass spectra to prove the existence of isotopes.
First artificially induced nuclear reaction. Used nitrogen and alpha particles to obtain an oxygen isotope and protons.
Created a model of successive orbital shells based o an equation of fixed radii and quantum numbers.
Louis Victor de Broglie
Electrons are similar to both particles and waves.
Werner Heisenberg, Max Born and Erwin Schodinger
Develop quantum mechanics
Used the frequencies based on spectra lines to describe atoms. The Principle of Indeterminacy states that you can not know the both the position and the velocity of a particular particle at any one moment in time.
Saw electrons as a continuous cloud and developed wave mechanics to be a mathematical model for the atom.
Suggested the existence of anti-particles. Found the first anti-electron, positron.
Discovered neutral atomic particle with similar mass to a proton, the neutron by using alpha particles.