History of Atomic Theory Project

Democritus

420

Discovered the existence of the ultimate particle

Daltons Atomic Theory

Nov 30, 1789

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

Antoine Lavoiser

Nov 30, 1789

proved the law of conservation of mass

Joseph Proust

Nov 30, 1799

Proposed the Low of Constant compositon-pure compound always contain the same elements in the same mass proportion.

John Dalton

Nov 30, 1803

Proposed the law of Multiple Proportions;pictured the atom as small industrutible particle wiht no internal structure.

law of definite proportons

Nov 30, 1806

states that a chemical compound always contains exactly the same proportion of elements by mass.

law of multiple proportions

Nov 30, 1808

statement that when two elements combine with each other to form more than one compound, the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers

JJ Thomas

Nov 30, 1897

Discovered negativly charged electrons, proposed the "Plum Pudding" model of the atom.

Cathode Ray Tube

Nov 30, 1897

is a vacuum tube containing one or more electron guns (a source of electrons or electron emitter) and a fluorescent screen used to view images

Plum Pudding Model

Nov 30, 1904

atom model

Robert Millikan

Nov 30, 1909

determined the unit charge of the electron. His discovery allowed for the calculation of the electron and all positively charged atoms.

Oil Drop Experiment

Nov 30, 1909

determined the size of the charge on an electron.

Gold Foil Experiment

Nov 30, 1910

to determine the layout of an atom

Ernest Rutherford

Nov 30, 1911

published an atomic theory in which the atom has a central positive nucleus surrounded by negative orbiting electrons.

Rutherford model

Nov 30, 1911

model of the atom

neils bohr

Nov 30, 1913

applied the quantum theroy to Rutherford's atomic structure and discovered a method of calculating the possible energy levels of stationary electrons. He also discovered that an emission of light occurs when an electron moves into a differnet energy level orbit.

bohr-planetary model

Nov 30, 1913

depicts the atom as small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus

Louis De Broglie

Nov 30, 1925

DIscovered that electrons could behave as waves under certain conditions.

electron cloud model

Nov 30, 1925

wherein electrons are no longer depicted as particles moving around the nucleus in a fixed orbit

Erwin Shrodiner

Nov 30, 1926

Developed the Shrodinger equation, can be used to predict the properties reactivities of all atoms and molecules, led to the atomic cloud model

Werner Heisenberg

Nov 30, 1926

Discovered the Heisenburg Uncertainty Principle, the momentum and position of a particle cannot be simultaneously measured with high precision.

Heisenberg Uncertainty Principle

Nov 30, 1927

is any of a variety of mathematical inequalities asserting a fundamental limit to the precision

James Chadwick

Nov 30, 1932

Confirmed the existence of the neutron.

law of conservation of mass

Nov 30, 1989

that mass is neither created or destroyed in ordinary chemical and physical changes.