Emmy Dickson

Question #1- EMMY DICKSON, CHEMISTRY 1st period

- 12 Major Scientists chosen to discuss:
Democritus, Lavosier, John Dalton, Demetri Mendeleev, J.J. Thompson, Ernest
Rutherford, Marie Curie, Mosely, Neils Bohr, Schrodienger, James Chadwick, Enrico
Fermi.

370 B.C.- Democritus composed the theory of "atoms", which are physically, but not geometrically, indivisible. He also stated that between atoms lies empty space; that atoms are indestructible and constantly in motion; that there are an infinite number of atoms, and kinds of atoms, which differ in shape, and size. Using analogies from our sense experiences, he gave a picture or an image of an atom that distinguished them from each other by their shape, their size, and the arrangement of their parts.

1700- Lavoisier became curious after the findings of Democritus and later defined what we know as "elements" today; substances that have definite chemical properties. Lavoisier built a Solar Furnace. This is the first example of a heliostat, which is a device used to concentrate sunlight. Many of his discoveries required a great deal of heat to burn off impurities from or cause reactions in the samples he was working with.

1800- John Dalton proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.
Atomic Theory:
1. All matter is composed of atoms
2. Atoms of the same element are alike in weight and other properties, atoms of
different emelements are different in weight and other properties.
3. Compounds are formed fromed by the union of separation of definitie number of atoms.
4. Atoms do not divide in chemical reactions; only whole atoms unite with other other
atoms.

1869- After Lavoisier discovered elements, Demetri Mendeleev arranged them 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.

1898- After Dalton stated the atomic theory, J.J. Thompson wanted to know more. He was investigating a long-standing puzzle known as "cathode rays." His experiments prompted him to make a bold proposal: these mysterious rays are streams of particles much smaller than atoms, they are in fact minuscule pieces of atoms. The rays are made up of electrons: very small, negatively charged particles that are indeed fundamental parts of every atom.

1898- While Rutherford was performing his various experiments in the field of radioactivity, bombarding nitrogen gas with alpha particles (alpha particles are a type of radiation), he noticed that one of the experimental results was a surge of hydrogen. He correctly deduced that the hydrogen atoms must have come from within the nitrogen atoms themselves, which would mean that there was something within all of these atoms which was divisible, the amount of which would determine what element the atom represented. He is known for the famous Gold Foil Experiment.

1898- After Rutherford studied the elements uranium and thorium, Marie Curie took these elements and called their spontaneous decay process "radioactivity". She and her husband Pierre also discovered the radioactive elements polonium and radium. She started taking elements and figuring out more information.

1914- After Mendeleev constructed the periodic table based on atomic weight, Henry G. Mosely used his work to reorganize the periodic table based upon atomic number instead. Using x-ray tubes, determined the charges on the nuclei of most atoms. He wrote"The atomic number of an element is equal to the number of protons in the nucleus".

1922- After all of this talk about atoms, Neils Bohr was the first to come up with an estimated structure of an atom. He developed an 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.

1930- Once J.J. Thompson had come up with the discovery of the electron, Schrodienger Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom.

1932- James Chadwick heard of a new method of detecting particles emitted by radioactive elements developed by Irene Joliot-Curie, one of Marie Curie's daughters, and her husband, Frederic. He used this new technique and discovered that there were different particles in the nucleus which were neutrally charged.

1942- After the majority of the basic knowledge needed to know about the atom, Enrico Fermi conducted the first controlled chain reaction releasing energy from the atoms nucleus.


3 ATOMIC MODELS:
Bohr, Thompson (plum mudding), Rutherford
each of these were revised by a later scientist who had gained more knowledge over the years and helped lead to the discovery of todays quantum model of the atomic structure.

Each of these scientists helped aid in each discovery to the next. Because of all these experiments, today's society now has a clear understanding of the atoms, the particles it makes up, and how atoms react with one another.

Source Helped:
http://www.cartage.org.lb/en/themes/sciences/physics/atomicphysics/atomicstructure/atomictimeline/atomictimeline.htm