History of the Atomic Model

Democritus

Oct 16, 1415

Democritus lived in the ancient Greek times.
He believed that all matter consisted of extremely small particles that could not be divided. He called these small particles "atoms". He also believed that there were different kinds of atoms;
LIQUIDS- round and smooth
SOLIDS- rough and prickly

Aristotle

Jan 10, 1417

Aristotle believed that there was not a limit to the number of times matter could be divided. His writing was not discovered until 1417.

John Dalton

Oct 31, 1803

Dalton believed that all matter was made up of induvidual particles called atoms, which cannot be divided.
- All elements are composed of atoms
- All Atoms of the same element have the same mass, and atoms of different elements have different masses
- Compounds contain atoms of more than one element
- In a particular compound, atoms of different elements always combine in the same way.

Joseph John Thomson

Oct 28, 1897

Thomson used a sealed tube of gas in his experiment. When the currents were on the disks became charged and a glowing beam appeared in the tube. When the charge was off, the beam bent toward a positively charged plate placed outside the tube. Thomson hypothesized that the beam was a stream of charged particles that interacted with the air in the tube. and caused the air to glow.

Hantaro Nagaoka

Oct 14, 1904

Hantaro Nagaoka suggested that an atom has a central nucleas. Electrons than circled around the atom like rings around saturn. Nagaoka created an early, incorrect model of an atom using an analogy based on Saturn’s rings.

Ernest Marsden

Feb 19, 1909

Marsden, with the help of han Geiger, conducted the Geiger-Marsden experiment also called the gold foil experiment. This experiment was conducted under Ernest Rutherford.

Ernest Rutherford

Oct 31, 1911

Rutherford thought that an atom has a dense, positively charged nucleus. Negatively charged particles move freely around the atom. Rutherford asked a student to find out what happens too alpha particles when they pass through a thin sheet of gold.

Neils Bohr

Nov 1, 1913

Bohr believeed that electrons moved around a positively charged nucleus at a fixed distance.

Louis de Broglie

Nov 2, 1924

Louis de Broglie belived that particles in the atom had a property almost like a wave. He used mathematical proportions.

Erwin Schrodinger

Nov 2, 1926

Schrodinger developed and used athematical equations to explain the motion of electrons in atoms. His work leads too a model including the electron cloud model.

James Chadwick

Nov 2, 1932

James Chadwick confirmed Erwin's model and the existence of neutrons.

Enrico Firmi

Nov 2, 1942

Enrico was the first to conduct the first controlled chain reaction releasing energy from the nucleus of the atom.