Atomic theory

Timeline in BC - AD

Period: 403 to Dec 31, 2000

Democritus

430

Stated that all matter is made up of atoms. They are invisible and enternal. Stating they couldnt be divided since they were so small and fill up an entire space they take on. Knowing they could not be seen but come in all shapes and sizes. Atoms correspond to substances they make and are building blocks.

John Dalton

Jan 3, 1803

Became a school teacher at age of 12. Made 4 assumptions: Matter made of atoms, are invisible. Atoms of an elemen are identical in mass and properties. They cant be created or destryoed. Rearrangement of atoms is a chemical reaction. Discovered the law of partial pressure stating: : pressure of a mixture of nonreactive gaseous elements is = to the sum of pressures each element of the mixture = same volume of mixture. Also developed law of stoichiometry, the foundation of atoms modern study

Amadeo Avogadro

Sep 13, 1811

Italian scientist. Avogadro’s law: theory of molarity and molecular weight. Stating = volumes of gas = number of particles. Invented term 'molecule'. Figuring three gases’ molecular weight = ratio of three gasses denisites under the continuous conditions of pressure and temperature. Statingsimple gases are compound molecules of two or more atoms instead of one solid atom. Avogadro changed the better of understanding molecules for scientists.

Dmitri Mendelev

Aug 19, 1869

Leader of the scientific revolution. Changed understanding of atoms through dedicating 13 years to collection & studying to develop the periodic table of elements & periodic law. Finding chemical properties of atoms demonstrated trends when the elements were arranged in order of increasing atomic mass.

Henri Becquerel

Dec 8, 1896

Discovered radioactivity through an experiment by exposing a uranium-bearing crystal to the sunlight. After having it placed in the sunlight for a while, he put the crystal on a photographic plate. Concluding the crystal would leave a mark on the photographic plate and it did.This experiment resulted in the theory that Uranium released engery from the sun in the form of X-Ray.

J.J Thomson

May 13, 1897

Discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube. Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of "bodies much smaller than atoms" that he calculated as having a very large value for the charge-to-mass ratio. Later he estimated the value of the charge itself. Later developed the mass spectrograph, later it was more advanced to discover isotopes.

Marie Curie

Dec 18, 1902

Inspired by Becquerel’s discovery of radioactivity, she discovered radiation through studying a range of uranium-containing compound. Leading her to the discover the strength of rays emitted from the atoms depended on the amount of uranium in that specific compound. Allowing her to develop methods for the characterization radium’s properties. Radium is essential for treatment for diseases.

Ernest Rutherford

Dec 18, 1911

Used the results of his gold-foil experiment to state that all the mass of an atom were in a small positively-charged ball at the center of the atom.

Niels Bohr

Sep 18, 1913

Based research on Rutherford, imposing that electrons orbit around the nucleas. Suggesting outer shells determind chemical properties of atom. Coming up with the theory radiation is emitted when electron s moves from an orbit which produce light.

Henri Moseley

Dec 18, 1914

Organized the chemical elements in periodic table in order of atomic number. Inventing the law of relationship between wavelength and the atomic number for each element. Also observed and measured different chemical elements by deflection of crystals through X ray scales.

Erwin Schrödinger

Dec 18, 1926

Developoed the quantum mechanical model, used in mathematical equations determining location of electrons in atom. Finding the more dense the cloud, it is easier to find location of electron. Sub energy concept was revealed due to this model.

Weiner Heisenberg

Apr 20, 1927

Through calculating subatomic particles and its behavior, observing patterns of electrons. Developing the uncertainty princible, which was electrons dont orbit in arranged formation. This helped scientists to understand depther into the atom, to compare number of the amount of atoms based on movement of electrons and the number they contain.