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Democritus
His atomic theory was that matter could not be divided into smaller peices forever. Eventually the smallest peice would be obtained and it would be invisible. -
Antoine Lavoisier
He is credited for "Law of conservation of mass in 1777.The Law of Conservation of Mass states that during chemical reactions matter is neither created or destroyed. The mass of the reactants should be equivalent to the mass of the products. -
Law of Conservation of Mass
Established in 1789 by French Chemist Antoine Lavoisier.
States that mass is neither created nor destroyed in any ordinary chemical reaction. Or more simply, the mass of substances produced (products) by a chemical reaction is always equal to the mass of the reacting substances -
John Dalton
Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. -
Daltons atomic theory
His Theory was that all matter is composed of atoms
atoms cannot be made or destroyed all atoms of the same element are identical different elements have different types of atoms chemical reactions occur when atoms are rearranged
compounds are formed from atoms of the constituent elements. -
Dmitri Mendeleev
Arranged elements 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. -
Cathode Ray Tube
Sir WIlliam Crookes discovered cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass. -
J.J. Thompson
Discovered the electron by using the Cathrode Ray Experiment. -
Plum Pudding Atomic Model
The plum pudding model of the atom by J. J. Thomson, who discovered the electron in 1897, was proposed in 1904 before the discovery of the atomic nucleus in order to add the electron to the atomic model. In this model, the atom is composed of electrons (which Thomson still called "corpuscles", 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 -
Robert Millikan
Deminstrated the atomic structure of electricity by doing the Oil Drop Experiment. -
Rutherford Model
-Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil . He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus.
-An atom's mass is mostly in the nucleus
-Electrons are in a fixed orbit -
Henry Moseley
He discovered that the number of protons of an element determines its atomic number. -
Niels Bohr
-Recognition of his work on the structure of atoms came with the award of the Nobel Prize for 1922.
-Planetary Model was used to prove that the nucleus was surrounded by orbiting electrons at different energy levels.
-Electrons have definite orbits -
Bohr Planetary
In the Bohr Model the neutrons and protons (symbolized by red and blue balls in the adjacent image) occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun (but the orbits are not confined to a plane as is approximately true in the Solar System). The adjacent image is not to scale since in the realistic case the radius of the nucleus is about 100,000 times smaller than the radius of the entire atom, and as far as we can tell electr -
Ernest Rutherford
He did the Electrical Structure of Matter. -
Quantum Mechanical Model
The quantum mechanical model is based on quantum theory, which says matter also has properties associated with waves. According to quantum theory, it’s impossible to know the exact position and momentum of an electron at the same time. This is known as the Uncertainty Principle. The quantum mechanical model of the atom uses complex shapes of orbitals volumes of space in which there is likely to be an electron. So, this model is based on probability rather than certainty. -
Erwin Schrodinger
A powerful model of the atom was developed by Erwin Schrodinger in 1926. Schrodinger combined the equations for the behavior of waves with the de Broglie equation to generate a mathematical model for the distribution of electrons in an atom. The advantage of this model is that it consists of mathematical equations known as wave functions that satisfy the requirements placed on the behavior of electrons. The disadvantage is that it is difficult to imagine a physical model of electrons as waves. -
Gold Foil Experiment
A large portion of Rutherford's research has always included the use and study of alpha particles ever since he classified them in 1898. Starting sometime around 1909, Rutherford began to notice that alpha particles would not always behave in accordance to the plum pudding model of an atom when fired at a piece of gold foil. These observations stimulated further research that was eventually published in 1911 and has been known ever since as Rutherford's Gold Foil Experiment. -
James Chadwick
He discovered neutrons, particles whose mass was close to that of a proton. -
Electron Cloud Model
Erwin Schrödinger built upon the thoughts of Bohr yet took them in a new direction. He developed the probability function for the Hydrogen atom (and a few others). The probability function basically describes a cloud-like region where the electron is likely to be found. It can not say with any certainty, where the electron actually is at any point in time, yet can describe where it ought to be. Clarity through fuzziness, is one way to describe the idea. The model based on this probability
