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460
Democritus
In 460 to 370 B.C., he was one of the first scientist to study the atom, and is the father of the atom. He said that all atoms are made of small, indivisible, indestructible particles. He also said that there are an infinite number of atoms, as well as different types of atoms that are different in shape and size. -
Law of Conservation of Mass
Mass of an iscolated system will stay constant over time. This principle is equivalent to the conservation of energy: when energy or mass is enclosed in a system and none is allowed in or out, its quantity cannot otherwise change over time. -
Antoine Laeisier
Lavoisier showed that diamonds and graphite were both forms of carbon by burning each to make carbon dioxide. He showed that candles burning and humans working both exhale carbon dioxide, pointing the way to understanding biochemistry and metabolism. -
John Dalton
John Daltons atomic theory made up of four postulates. All matter is made up of atoms.Atoms cannot be made or destroyed. All atoms of the same element look the same.Different elements have different types of atoms.Chemical reactions occur when atoms are rearranged
Compounds are formed from atoms of the constituent elements. -
Daltons atomic theory
His atomic theory said that elements are made of extremely small particles called atoms.Atoms of a given element are the same in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.Atoms cannot be subdivided, created, or destroyed.Atoms of different elements combine in simple whole-number ratios to form chemical compounds.In chemical reactions, atoms are combined, separated, or rearranged. -
Dmitri Mendeleev
Proposed the periodic law and developed the first periodic table in 1869. Medeleev's table was arranged according to increasing atomic weight and left holes for elements that were yet to be discovered. -
Henry Moseley
Developed the X-ray spectra to study atomic structure, Moseley's discoveries resulted in a more accurate positioning of elements in the Periodic Table by closer determination of atomic numbers. -
Cahode Ray Tube
A cathode ray tube is a glass tube that has a wire passing through both ends. An electrical current is passed through this wire from the cathode (negative terminal) to the anode (positive terminal). Cathode rays travel along the wire in a vacuum, producing a beam of light.Thomson thought that the cathode rays had a negative charge.In 1895, Jean Perrin set out to confirm Thomson's speculation that cathode rays carried a negative charge. -
J.J. Thompson
He discovered that electrons are parts of atoms in his cathode-ray tube experiment, each atom as little plum pudding models, with the electrons suspended in a "pudding" or mass of positively charged particles. -
Plum Pudding Atomic model
An atom is composed of electrons though G. J. Stoney had proposed that atoms of electricity be called electrons in 1894 surrounded by a soup of positive charge to balance the electrons' negative charges, like negatively charged "plums" surrounded by positively charged "pudding". The electrons were thought to be positioned throughout the atom, but with many structures possible for positioning multiple electrons, particularly rotating rings of electrons. -
Gold Foil Experement
He put gold foil with alpha particles, and observing the scattering of these particles, a procedure requiring many hours in a dark room watching for little flashes of light as the scattered particles struck a scintillant screen. Rutherford was surprised to seethat most of the particles passed through the foil without any deflection;proved that atoms were made up of mostly empty space,with an extremely small center core. -
Robert Millikan
Millikan made a lot momentous discoveries, chiefly in the fields of electricity, optics, and molecular physics. His earliest major success was the accurate determination of the charge carried by an electron, using the elegant "falling-drop method"; he also proved that this quantity was a constant for all electrons . demonstrating the atomic structure of electricity. -
Rutherford Model
Rutherford took away the Plum Pudding model and said the only way the alpha particles could be deflected backwards was if most of the mass in an atom stayed in the nucleus. He then created the planetary model of the atom which put all the protons in the nucleus and the electrons orbited around the nucleus like planets that orbit around the sun. -
Bohr Planetary Model
He stated that the outer orbits could hold more electrons than the inner ones, and the outer orbits determine the atom's chemical properties. Bohr 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. -
Niels Bohr
Bohr's model was the theory that electrons travel in discrete orbits around the atom's nucleus, with the chemical properties of an element being largely determined by the number of electrons in its outer orbit.The idea that an electron could drop from a higher-energy orbit to a lower one, taking out a photon of discrete energy. This explained a lot of spectropscopy and became the basis for quantum theory. -
Electron Cloud Model
The electron cloud model is an atom model where electrons are no longer said to be particles moving around the nucleus in a fixed orbit. Instead, as a quantum mechanically influenced model, don't know exactly where they are, and cant describe their probable location around the nucleus as a powerful cloud. -
Ernest Rutherford
He made the theory of the atom through his discovery of the scattering of alpha particles off the nucleus with his gold foil experiment.Demenstrated radioactivity and the integration of atoms. -
Quantum Mechanical Model
Is based on the quantum theory which describes how matter also has properties associated with waves. It also tells the exact position and momentum of an electron at the same time. Used complex shapes of electron clouds. It is using more probibility than certainty. -
Erwin Schrodinger
The Schrödinger model assumes that the electron is a wave and tries to describe the regions in space, or orbits, where electrons are most likely to be found. Instead of trying to tell where the electron is at, the Schrödinger model describes the probability that an electron can be found in a given region of space at a given time. This model no longer tells us where the electron is; it only tells us where it might be. -
James Chadwick
James Chadwick proved the existence of neutrons. As uncharged particles in atoms, neutrons play a key part in nuclear fission, or the splitting of atoms.Chadwick's research greatly increased understanding of the structure of the atomic nucleus. Before his discovery, scientists knew of the existence of protons in the nucleus, but not neutrons.
