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450
Democritus
In 450 B.C. Democritus predicted that all matter was made of small particles, which he called atoms, floating in a vacuum, and believed that atoms could not be created, destroyed,or further divided. -
Law of Conservation of Mass
In the late 18th century the Law of Conservation of Mass- stated that during mass is neither created nor destroyed during a chemical reaction- it is conserved; was discovered in chemical reactions by Antoine Lavoisier. -
Antoine Lavoisier
In the late 1790s Lavoisier performed some of the first quantitative chemical experiments; his data and observations led to the statement of the law of conservation of mass. He was one of the first to use an analytical balance, Mass reactants = Mass products. He also compiled a list of elements. (23 known at the time) -
John Dalton
John Dalton revived and revised Democritus's ideas. Dalton's atomic theory explains the conservation of mass in chemical reactions as being the resulty of the separation, combination, or rearrangement of atoms; atoms that are not created,destroyed,or divided in the process.Dalton's experimental evidence and clear explanation of the composition of compounds and conservation of mass led to his atomic theory. -
Dalton's Atomic Theory
Dalton's Atomic Theory
All matter is composed of extremely small particles called atoms.
All atoms of a given element are identical, having the same size, mass and chemical properties. Atoms of any other elements.
Atoms cannot be created,divided into smaller particles, or destroyed.
Different atoms combine in simple whole-number ratios to form compounds.
In a chemical reactions, atoms are separated, combined or rearranged. -
Dmitri Mendeleev
Mendeleev devised the chart that organized all of the elements taht were known at the time into rows and columns based on their similarities and their masses, which has been further devloped into the periodic table of elements. He was also able to predict the properties of elements that were yet not discovered (at the time). -
Cathode Ray Tube
Cathode ray tube is a ray of radiation that originates from the cathode and travels to the anode of a cathode ray tube. -
J.J Thomson
J.J.Thomson began a series of cathode ray tube tube experiments in the late 1890s to determine the ratio of its change to its mass. He was able to determine the charge-to-mass of the charged particle; he was also concluded that the mass of the charged particles was much less than that of a hydrogen atom the lightest know atom. He also identified the first subatomic particle- the electron. He proposed a model of the atom that became known as the plum pudding model. He discovered electrons. -
Electron Cloud Model
In the early 1900s the electron cloud model was introduced. The electron cloud model is an atomic model where in electrons are no longer depicted as particles moving around the nucleus in a fixed orbit. -
Plum Pudding Model
Was proposed by J.J Thomson consisted of a spherically shaped atom composed of a uniformly distributed positive charged electrons resided. -
Gold Foil Experiment
The gold foil experiment was performed to find out the entire mass of atoms the unexpected results of the experiment demonstrated for the first time the existence of the atomic nucleus, leading to the downfall of the plum pudding model and the development if the Rutherford Model. -
Robert Millikan
Millikan determined the mass of the electron -> mass of a hydrogen. -
Ernest Rutherford
Rutherford discovered protons positively charged particles using the gold foil experiment he determined that atoms were made up of mostly empty space the which the electrond moved, and that there was a tiny denes region called the nucleus that holds all the positively charged particles and most of its mass. -
Rutherford Model
Rutherfords model described the atom as a tiny dense, positively charged core called a nucleus, in which nearly all mass is concentrated around which the light electrons, circulate at some distance much like the planets revolving around the Sun. -
Niel Bohn
Bohr proposed a quantum model for the hydrogen atom that helped answer why elements atomic emission spectra is discontinuous rather than being continuous. -
Bohr Planetary Model
This model was introduced by Niel Bohr in 1913, it is a modification of the earlier Rutherford model, it describes most of the accepted features of the atomic theory without all ofv the high-level math of the modern version. The electrons orbit a small, positively-charged nucleus like the planets orbiting the Sun. The energy of the orbit is related to its size. The lowest energy is found in the smallest orbit. Radiation is absorbed or emitted when, an electron moves from one orbit to another. -
Henry Moseley
Henry Moseley discovered that atoms of each element contains a unique positive charge in their nuclei. Thus, the number of protons in an atom identifies it as am atom of a particular element. By arranging the elements in oder of increasing atomic number instead of increasing atomic mass, as Mendeleev had done, the problems with the order of the elements in the periodic table were solved. Moseley's arrangement if elements by atomic number resulted in a clear periodic pattern of properties. -
Ernest Rutherford
Rutherford concluded that the nucleus was made up of positively charged particles called protons, 1+ charge. -
Erwin Schrodinger
Erwin Schrodinger stated that rather than electrons distributed within an electron configuration of shells and energy levels, they were arranged in orbital, which are subatomically distributed. -
Quantum Mechanical Model
The Quantum Mechanical model is a model that uses complex shapes or orbitals (electron clouds) of the electrons in an atom. -
James Chadwich
He discovered that the neutron has no charge and that it is found in the nucleus. He also said that atoms are spherically shaped, have a tiny, dense nucleus with a positive charge, electrons that move around the nucleus.
