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Democritus
•Did not conduct any experiments
•All matter is made of atoms
•Atoms are indivisible and indestructible
John Dalton
John Dalton was born on September 6, 1766 in Cumbria, England.
He provided us with the first concrete ideas about the atom.
John Dalton
Four points to his theory:1. All matter is composed of atoms that are
indestructible and indivisible 2. Atoms of one element are all the same; atoms of a
different element are different (Au atoms are different from Ag atoms)
3. Atoms cannot be changed into different atoms by chemical of physical changes (Pb atoms cannot be turned into Au atoms)
4. All atoms are like Billiard Balls – a solid, sphere5. Atoms react in whole numbers
JJ Thomson
Joseph John Thomson was born in Cheetham Hill, a suburb of Manchester on December 18, 1856.
He is given credit for the discovery of the electron.
JJ Thomson
3 Points to his theory
1. * All gases had the same mass: charge ratio
2. * All atoms contain small, charged particles called electrons
3. * The atom now looked like “Plum Pudding”
Goldstein
Major Point to his theory
He is given credit for the discovery of a positively charged particle = Proton
The atom was still thought to resemble Plum Pudding
Millikan
2 Points to his theory
1. All electrons have the same mass About 1/2000 atomic mass unit
2. All electrons have the same charge -1.6 x 10 -19 Coulomb
The atom was still thought to resemble Plum Pudding
Rutherford
3 Points to his theory1. * Most alpha particle
went through = Atom is mostly empty space (area of electrons)
2. * Some alpha particles bounced straight back = atom has a solid mass (nucleus)
3. * Some alpha particles reflected = nucleus is positively charged
New Model = Nuclear Model
Schrödinger
Major points1. Electrons do not follow
fixed paths2. They move randomly in
areas of probability (orbitals)
3. There are specific energies associated with each orbital
New Model = Quantum Mechanical Model