Chem Unit 3: Atomic Structures- AS.1

The 2 ancient Greek philosophers and their ideas

Aristotle- Matter is continuous and not made of smaller particles

Democritus- World was made of 2 things: Empty space and atoms

(Neither had evidence so they were not given credit)

1st foundational law, found by Antoine Lavoiser (French) in 1782

Law of conservation of matter-matter is neither created or destroyed, just rearranged

2nd foundational law, found by Charled Coulomb in 1785

Law of electrical charges-opposite charges attract and like charges repel

3rd and 4th foundational law, found by Joseph Proust (French) in 1799

Law of definate proportions-Atoms must combine in whole number ratios

Law of multiple proportions-Atoms can combine in different whole number ratios

John Dalton (1839)

father of modern atomic theory

Daltons Atomic Theory

• All matter is made up of atoms. Atoms are the smallest fundamental units of matter (True today)

• All elements consist of atoms which are indivisible and indistructable (False-nuclear reactions)

• All atoms of the same element are identical in size, shape, and mass (false-isotopes)

• Atoms of different elements are different in size, shape, and mass (true)

• In a chemical reaction, atoms are rearranged, never created nor destroyed and they combine in whole number ratios (true)

Daltons atomic model:

• Lacks subatomic particles

• solid sphere

• everything else is empty space

JJ Thomsom

Cathode Ray Experiment

Thomson’s Plum-Pudding Model

-Concluded all atoms contained electrons. Since all atoms were neutral, there must be some positive change spread throughout the atom to balance the negative and keep the atom neutral.

-PROBLEM: No nucleus

Ernest Rutherford ( Thomson’s Student)

Gold foil model

results of gold foil experiment:

• Most of the positive charges passed through because the atom is mostly empty space

• Some of the positive charges deflected because the atom contains some possible charge

• Some of the positive charges deflected straight back because there is a concentrated area of positive charge (Nucleus)