Lilliona's Atomic Model

Democritus

400

In 400 B.C. Democritus thought that there wre different types of atoms with specific sets of properties. The atoms in liquids were round and smooth, but the atoms in solids were rough and prickly.

Aristotle

500

In 500 B.C. Aristotle did not think there was a limit to the number of times matter could be divided. He thought that all substances were built up from only four elements- earth, air, fire, and water. The elements were a combination of four qualities- hot, cold, dry, and wet.

John Dalton

Aug 25, 1803

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. He made wooden spheres to represent the atoms of dfferent elements. Each type of atom is represented by a tiny, solid sphere with a different mass.

J.J. Thomson

Jul 25, 1897

J.J. Thomson pictures electrons embedded in a sphere of postitve electric charge. He used an electric curent to learn more about atoms. He used a device that has a sealed glass tube from which most of the air has been removed. Metal disks are on the end of the tube. Wires connect metal disks to the source of electric currents. When the current is turned on negatively charged and another positive. A glowing beam forms between the disks.

Hantaro Nagaoka

Oct 31, 1904

In 1904, Nagaoka developed an early, incorrect planetary model of the atom. The model was based around an analogy to the explanation of the stability of the Saturn rings. The model made two predictions:
1.a very massive nucleus.
2.electrons revolving around the nucleus, bound by electrostatic forces.

Ernest Marsden

Oct 31, 1909

Marsden was Rutherford's student. Rutherford asked him to find out what happens to alpha particles when they pass through a thin sheet of gold. He aimed a narrow beam of alpha particles at the gold. The screen around the gold was made of a material that produced a flash of light when struck by a fast-moving alpha particle.

Ernest Rutherford

Feb 22, 1911

Ernest Rutherford said that an atom has a dence, positively charged nucleus. Electrons move randomly in the space around the nucleus. According to Rutherford's model all of an atom's postive charge is concentrated in it's nucleus

Niels Bohr

Jan 29, 1913

Niels Bohr said that the electrons move in spherical orbits at fixed distances from the nucleus. He applies the Quantum theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits defined by their angular momentum. This led to the calculation of possible energy levels for these orbits.

Louis de Brogile

Oct 30, 1924

Louis de Brogile propses that moving particles like electrons have some properties of waves. Within a few years evidence is collected to support this idea. This helped scientists understand that the atom didn't behave like the solar system because electrons do not move in regular orbits.

Geiger

Oct 31, 1925

Geiger demonstrated that energy and mass are conderved in atomic processes.

Erwin Schrodinger

Oct 30, 1926

Schrodinger develops mathematical equations to describe the motion of electrons in atoms. His work leads to the electron cloud model.

Otto Hahn

Oct 31, 1938

Hahn found that when Uranium is bombarded by neutrons it produces smaller nuclei roughly half the size of the original Uranium nucleus.

James Chadwick

Oct 30, 2011

Chadwick comfirms the existence of neutrons, which have no charge. Atomic nuclei contain neutrons and positively charged protons.