1. Atomic Theory
A Brief History

2. Democritus
Greek Philospher who first thought matter was made up of tiny particles called atomos
He thought atoms were solid, homogeneous, and indestructible.
He also thought atoms moved through empty space.
Aristotle thought Democritus was wrong and everyone believed him.

3. Basic Laws to Describe Matter
In the 1790s better balances were used to study the masses of various elements and compounds  this lead to three laws
The law of conservation of mass = mass is neither created nor destroyed
C + O  CO
The law of definite proportions = a compound contains the same elements in exactly the same proportions
NaCl, H2O
The law of multiple proportions = If two or more different compounds are composed of the same two elements, then the ratio of the masses are small whole numbers
CO and CO2

4. John Dalton (1808)
English school teacher: began modern atomic theory, he revised Democritus’s ideas to for his atomic theory
Matter is made up of tiny particles called atoms
Atoms of an element are identical
Atoms can’t be subdivided, created or destroyed
Atoms of different elements combine in whole # ratios to form compounds
In chemical reactions, atoms are combined, separated, or rearranged

5. J.J. Thomson (1897)
His studies supported the hypothesis that particles in the cathode ray are negatively charged
He discovered the electron using the cathode ray tube experiment
He came up with the plum-pudding model of the atom.

7. J.J. Thomson (1897)
His studies supported the hypothesis that particles in the cathode ray are negatively charged
He discovered the electron using the cathode ray tube experiment
He came up with the plum-pudding model of the atom. -

8. Ernest Rutherford(1911)
New Zealand Chemist: discovered the nucleus of an atom using the gold foil experiment.
He also discovered the presence of protons within the nucleus. +

9. Chadwick
A coworker of Rutherford, he discovered the presence of neutrons within the nucleus.
Neutrons are particles the same size of protons but with no charge +n

10. Bohr
He believed that the nucleus was in the center of the atom, containing the protons and neutrons.
His atomic model has the electrons outside the nucleus traveling in paths called “energy levels”. +n

11. Schrodinger: Modern Atomic Theory
nucleus that
contains protons
and neutrons +n
electrons surround
nucleus in a “cloud”