PRESENTATION OUTLINE
Democritus- 460 BC
-Formulated what is thought to be the first atomic theory.
-Some people consider him to be the father of modern science.
-Claimed that everything is made up of atoms. Those atoms are physically, but not geometrically, indivisible.
-Between atoms lies empty space. Atoms are indestructible, have always been, and always will be, in motion.
-There are an infinite number of atoms and kinds of atoms, which differ in shape, and size.
Antoine Lavoisiser-1772
-Credited as the “father of modern chemistry."
-He formulated a theory of the chemical reactivity of oxygen and co-wrote the modern system for the nomenclature of chemical substances.
-He started working on processes like combustion, respiration and the calcination or oxidation of metals.
-He later introduced a chemical element in its modern sense and demonstarted how it should be implemented by composing the first modern list of the chemical elements.
Law of Conservation of Mass- 1789
-Established by French Chemist Antoine Lavoisier
-States that matter can be changed from one form into another, mixtures can be separated or made, and pure substances can be decomposed, but the total amount of mass remains constant.
-The mass of substances produced (products) by a chemical reaction is always equal to the mass of the reacting substances (reactants).
John Dalton- 1803
-Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.
Dalton's Atomic Theory- 1808
-If two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers.
Dimitri Mendeleev- 1860
-He began working on his great achievement: the periodic table of the elements. By arranging all of the 63 elements then known by their atomic weights, he managed to organize them into groups possessing similar properties. Where a gap existed in the table, he predicted a new element would one day be found and deduced its properties. And he was right.
Henry Moseley- 1887
A British chemist, who studied under Rutherford and brilliantly developed the application of X-ray spectra to the study atomic structure. His discoveries resulted in a more accurate positioning of elements in the Periodic Table by closer determination of atomic numbers.
J.J. Thompson-1897
-Believed that cathode rays are charged particles...Which he called corpuscles. These corpuscles are constituents of the atom.
-These corpuscles are the only constituents of the atom.
-Thomson proposed a model, sometimes called the "plum pudding" model, in which thousands of tiny, negatively charged corpuscles swarm inside a sort of cloud of massless positive charge.
Cathode Ray Tube- 1897
-A cathode ray is a stream of electrons leaving the negative electrode, or cathode, in a discharge tube (an electron tube that contains gas or vapor at low pressure), or emitted by a heated filament in certain electron tubes.
Gold Foil Experiment- 1899
-Established by Ernest Rutherford.
-The experiment shot minute particles at a thin sheet of gold. It was found that a small percentage of the particles were deflected, while a majority passed through the sheet. This caused Rutherford to conclude that the mass of an atom was concentrated at its center.
-Proved the existance of a small massive center to atoms, which would later be known as the nucleus of an atom.
Plum Pudding Atomic Model- 1904
-Proposed by JJ Thomson, the physicist who discovered the electron.
-The idea that atoms of electricity be called "electrons", surrounded by a soup of positive charge to balance the electrons' negative charges, like negatively charged "raisins" surrounded by positively charged "pudding".
Rutherford's Model- 1909
-The atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance.
Robert Milikan- 1910
-His first major success was accurate determination of the charge carried by an electron, using the "falling-drop method."
-He also proved that this quantity was a constant for all electrons, demonstrating the atomic structure of electricity.
Ernest Rutherford- 1911
-Studied radiations emitted from uranium and thorium and named them alpha and beta.
- He established that the nucleus was: very dense,very small and positively charged. -He also assumed that the electrons were located outside the nucleus.
Quantum Mechanical Model- 1913
-Proposed that electrons are arranged in concentric circular orbits around the nucleus. -
This model is patterned on the solar system and is known as the planetary model.
Bohr Planetary Model- 1913
-He published a theory about the structure of the atom based on an earlier theory of Rutherford's.
-Expanded upon this theory by proposing that electrons travel only in certain successively larger orbits.
-He suggested that the outer orbits could hold more electrons than the inner ones, and that these outer orbits determine the atom's chemical properties.
-Also described the way atoms emit radiation by suggesting that when an electron jumps from an outer orbit to an inner one, that it emits light. Later other physicists expanded his theory into quantum mechanics. This theory explains the structure and actions of complex atoms.
Electron Cloud Model- 1920s
-Represents a sort of history of where the electron has probably been and where it is likely to be going.
-Area around the nucleus of an atom where electrons are most likely to be found.
Niels Bohr- 1922
-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.
Erwin Schrödiner- 1926
-Developed the theory that electrons absorb and emit radiation of fixed wavelengths when jumping between the fixed orbits around a nucleus.
-Showed a number of fundamental results in the field of quantum theory, which formed the basis of wave mechanics.
James Chadwick- 1932
-He pursued the fundamental discovery in the domain of nuclear science: James proved the existence of neutrons - elementary particles devoid of any electrical charge.
-James prepared the way towards the fission of uranium 235 and towards the creation of the atomic bomb.
