ATOMIC STRUCTURE

Scientists that changed our view of the atom

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 – His Experiment

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 – His Experiment

Cathode Ray Tube

JJ Thomson – His Experiment

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

Eugene Goldstein was born in 1850 in Germany.

Goldstein – His Experiment

Cathode Ray Tube

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

Robert Andrews Millikan was born on the 22nd of March, 1868, in Morrison, Ill. (U.S.A. )

Millikan – His Experiment

Oil Drop

Experiment

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

Ernest Rutherford was born August 30, 1871 in Nelson, New Zealand (one of 12 children)

Rutherford – His Experiment

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

Erwin Schrödinger born August 12 in Vienna, Austria in 1887.

Schrödinger – His Experiment

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

Chadwick

James Chadwick was born in Cheshire, England, on 20th October, 1891.

Chadwick – His Experiment

Chadwick

2 Points to his theory

1. Discovered the Neutron – Same mass as a proton, but without a charge

2. Mass could be converted into energy

Model was still thought to resemble the Quantum Mechanical Model