SCIENCE TIMELINE

DEMOCRITUS (460 BC- 370 BC)

• At some point when dividing matter, you will reach a point when it's indivisible
• The piece of matter that he called this was an "atomos" meaning indivisible.

DEMOCRITUS'S MODEL CREATED IN 440 BC

JOHN DALTON (9/6/1766-7/27/1844)

• All matter is made of atoms.
• Atoms are indivisible and indestructible.
• All atoms of a given element are identical in mass and properties.
• Atoms join together to make substances

DALTONS MODEL CREATED IN1803

WILLIAM CROOKES (6/17/1832-4/14/1919)

• Identified the many properties of the cathode rays.
• These rays move in a straight line and cause glass to glow
• Also they carry negative charges.
• They are capable of being deflected by electric fields too

WHAT HIS RAY LOOKED LIKE, CREATED IN 1879

HENRI BECQUEREL (12/15/1852-8/25/1908)

• Discovered radioactivity

HIS ATOMIC MODEL

HIS PLUM PUDDING MODEL

ERNEST RUTHERFORD (8/30/1871-10/19/1973)

• Realized that atoms have all of its mass condensed at its center, in a nucleus.
• Composed this off of a gold foil experiment.
• Showed that nucleus take up one billionth volume of the atom

HIS GOLD FOIL EXPERIMENT

HIS MODEL

PIERRE (1859-1906) AND MARIE CURIE (1895-1906)

• Radioactive materials cause atoms to break down losing radiation in the form of energy
• Discovered the elements radium and polonium.

THIS IS THE CURIES EXPERIMENT

NIELS BOHR (10/7/1885-11/18/1962)

• Neils Bohr refined Rutherford's model in 1913 by proposing that electrons...
• I. orbit the nucleus without losing energy
• II. could move only in fixed orbits of specific energies.
• III. electrons with low energy will orbit closer to the nucleus.
• IV. electrons with high energy orbit further from the nucleus.

BOHR'S MODEL CREATED IN

JJ THOMSON (12/16-1856-8/30/1940)

• Proposed plum pudding model of an atom
• Discovered electrons
• An atom consists of positive charge with negative charges in bedded in it
• Positive and negative charges are equal in magnitude to they cancel out

JAMES CHADWICK (10/20/1891-7/24/1974

• established that atomic number is the number of protons in an atom.
• discovered the fourth subatomic particle,the neutron
• most famous for his discovery of the neutron in an atom in 1932.

CHADWICK'S MODEL

WERNER HEISENBERG (12/5/1901- 2/1/1976)

• Electrons confined in their orbits would set up standing waves
• These formed regions of space about the nucleus were called orbitals
• Orbitals could be described as electron density clouds.
• In the densest area you have the greatest probability of finding electrons
• In the least dense area you have the least probability of finding electrons

ERWIN SCHRÖDINGER (8/12/1887-1/4/1961)

• Same as Heisenberg

THEIR MODEL CREATED IN