History of the Atom

1
History of the Atom

• Scientists who shaped the modern atomic theory

2
4th Century Greece

• Democritus
• first suggested matter was made of atoms
• there was no way to test these theories

• Aristotle
• suggested matter was continuous, not made of
  atoms
• this was believed

3
Alchemists

• Transmutation tried to turn all metals into gold
• brought observation and experimentation to
  science

4
Antoine Lavoisier

• In ordinary chemical reactions in a closed
  system, mass remained constant.
• Law of conservation of mass
• matter can not be created or destroyed

5
John Dalton and the Atomic Theory

• In the early 1800s, Dalton wrote explanations of
  the atom based on experiments by Lavoisier and
  Proust.

6
Daltons Atomic Theory

• Atoms are indivisible.
• Elements are made of atoms.
• Atoms of the same element are identical. Atoms
  of different elements are different.
• Atoms combine in simple, whole number ratios.
• Reactions occur when atoms are separated or
  combined.

7
J.J. Thomson

• 1897
• cathode rays are composed of electrons
• determined the charge of an electron
• plum pudding model

8
(No Transcript)
9
In the early 1900s...

• Robert Millikan (American)
• oil drop experiment
• accurately measured the charge of an electron

10
Then a ray of light??

• 1896
• Henri Becquerel discovered that uranium exposes
  photographic film.
• Radioactivity

• Early 1900s
• Marie and Pierre Curie discovered that rays are
  given off by uranium and radium.
• Atoms will split into smaller units

11
Albert Einstein

• Explained the origin of the energy produced in
  nuclear reactions with E mc2.

12
Then the modern theory began to develop

• Lord Rutherford
• 1913
• Proved Thomson
• wrong

13
Rutherford Model

• Also called the planetary model
• Most of the atom is empty space
• Consists of a central nucleus surrounded by
  electrons in orbits

14
The final particle is discovered...

• 1932
• James Chadwick
• found particle with the same mass as a proton,
  but no charge
• now known as a neutron

15
So what did this all mean to the atomic theory?

• Daltons theory had to be revised to include
  subatomic particles!

16
Bohr Model

• Calculated specific energy levels for electrons

17
Quantum mechanical model(Schrodinger, de
Broglie, Heisenberg)

• Current model
• Electron cloud model
• Electrons do not have fixed positions, but exist
  somewhere in the electron cloud