Evolution of Atomic Model

1803, 1808 (English man)                                                 
John Dalton: "Bring back the atom: a solid sphere"

• All matter is made of atoms
• Each element has: 
• own type of atoms 
• predictable ratios.

1897 (English man)

Joseph John Thomson’s Model

The atom has random negative and positive charges, but stays neutral. Keeps together and there are negatively charged particles that surround the nucleus.

His experiment: the plum-pudding;  electrons acted as the plums and got stick on the pudding- nucleus. 

1911 (New Zealand)

Rutherford: "Atoms have a center"

• Discovers the nucleus of the atom

1913 

Niels Bohr: Puts electrons into orbit

• Electrons:
• move in well-defined orbits
• can jump to different orbits to emit or absorb energy
• Almost all of the atom is empty space

1919 (U.S)

G.N. Lewis & Irving Langmuir

• Atoms form bonds by sharing electrons

1960s

Smaller particles discovered

• Protons and neutrons are made of even smaller particles: quarks

1980s

Tunneling to the Atom Level

• Scanning tunneling microscopes (STMs)
• scientists interact with matter at an atomic level
• get accurate pictures