1.1 Atomic Theory

%%atom:%% the smallest particle having properties of an element.

%%element:%% substance that cannot be broken down into simpler substances.

The Greeks (400 B.C.)

• Aristotle: deduced that all matter was made of 4 elements
  • @@ex: fire, air, water, and earth@@

Democritus (350 B.C.)

• Greek philosopher
• matter is not infinite
• “atomos”= indivisible
• atoms move in empty space
• no experiments to support the idea

Alchemy

• believed they could turn any cheap metals to gold
• almost like magicians

Contributions of Alchemists

• ==mercury, sulfur, and antimony==
• properties of some other elements
• ==production of gunpowder==

John Dalton

• beginning of modern atomic theory

• ^^billiard ball model^^

  

Theories

• all matter is composed of atoms
• all atoms of a pure element are identical
• different atoms combine in whole number ratios to form compounds
• ==atoms are separated, combined, rearranged in chemical reactions==

Size of an atom

• nucleus is tiny compared to an atom

Basic Structure

• atoms can be divided into 3 subatomic particles (electron, proton, and neutron)

John Thomson (1904)

• ^^Plum pudding model^^ (electrons embedded in positively charged nucleus)

• ==electrons, isotopes, mass spectrometer==

  

Earnest Rutherford

• ^^nuclear model,^^ almost all of the mass was in the nucleus, positively charged

credited with discovery of: ==protons and dense nucleus==

99.97% of atom’s mass is in nucleus, 0.0001% in volume

Bohr

• ^^planetary model^^, electrons travel in fixed orbits

• orbit determined by electrons’ energy

  

Schrodinger

• math to determine where the electrons are

Chadwick

• confirmed existence of neutrons