History%20of%20Chemistry

1
History of Chemistry

• Discoveries and Atoms

2
Early Greeks

• Democritus all matter is made of small,
  indivisible particles called atomos
• Aristotle matter is continuous and NOT made of
  smaller particles

3
Robert Boyle (1600s)

• 1st true chemist
• Discovered a relationship between pressure and
  volume (Boyles Law)

4
Antoine Lavoisier

• Matter cannot be created or destroyed
• Law of Conservation of Mass

5
Joseph Proust

• Found that a given compound always contains
  exactly the same proportion of elements by mass
• Law of Definite Proportions

6
John Dalton (1800s)

• The ratios of the masses of elements in a
  compound can always be reduced to small whole
  numbers
• Law of Multiple Proportions

7
Daltons Atomic Theory

• 1) all matter is composed of tiny particles
  called atoms
• 2) the atoms of an element are always identical
  while the atoms of different elements are
  different
• 3) compounds form when atoms combine atoms
  combine in small whole number ratios
• 4) reactions involve reorganization of atoms
  the atoms themselves do not change

8
Dalton

• Proposed the Billiard-ball model of the atom

9
Joseph Gay-Lussac (1809)

• Measured the volumes of gases that reacted with
  one another to develop the
• Law of Combining Volumes of Gases

10
Amadeo Avogadro

• at the same temperature and pressure, equal
  volumes of gases contain the same number of
  particles
• Avogadros hypothesis

11
J.J. Thomson

• Produced a cathode ray which was deflected by a
  negative electric field
• Thus the ray must be made of negative particles
  (electrons)

12
J.J. Thomson

• Since atoms are neutral, they must also have a
  positive area
• Plum pudding model

13
J.J. Thomson

• Protons were found to be 1836 X the mass of an
  electron
• Charge of proton is 1

14
Robert Millikan

• Oil drop experiment to determine the magnitude of
  the electrons charge
• which is now known as -1

15
James Chadwick

• Discovered high energy particles with no charge
  and the same mass as the proton
• the neutron

16
Henri Becquerel

• Accidentally discovered radioactivity
• Alpha particles (2 charge)
• (Also beta particles, gamma rays)

17
Ernest Rutherford (1911)

• Tests Thomsons Plum Pudding Model by shooting
  alpha particles through a sheet of gold foil

18
Ernest Rutherford

• Nuclear Model of the Atom

19
Robert Bunsen

• Found that when heated, different elements
  produced different colors in a flame

20
Niels Bohr (1912)

• Electrons orbit the nucleus somewhat like
  planets orbit the sun
• Planetary Model

21
Arnold Sommerfeld

• Expanded the Bohr model
• Electrons travel in orbitals, but
• the orbitals are not the same shape
• -- this leads to the electron cloud model of the
  atom

22
Electron Cloud Model
23
Wolfgang Pauli (1924)

• Predicted that electrons spin while orbiting the
  nucleus
• Paulis Exclusion Principle says no two
  electrons do the exact same thing at the same time

24
de Broglie and Schrödinger

• Propose that electrons move like wave
• thus the Wave-Mechanical Model

25
Werner Heisenberg

• No experiment can measure the position and
  momentum of a quantum particle simultaneously
• Heisenbergs Uncertainty Principle

26
Modern View of the Atom

• Tiny nucleus surrounded by electron cloud
• Nucleus accounts for all of the mass
• Arrangement of electrons causes different
  chemical properties

27
Electron Cloud Model

• Note Just as no map can equal a territory, no
  concept of an atom can possibly equal its nature.
  These models of the atom simply served as a way
  of thinking about them, though they contained
  limitations (all models do).