Greek philosophers marked the beginning of our understanding of matter.
The Four Element Theory: (lasted for about 2000 years!)
- According to a Greek philosopher called Aristotle, all matter is comprised of four elements: earth, water, air and fire.
- First mention of atoms!!!
In 300 BC, Democritus, a Greek philosopher said atoms were indivisible particles.
Lavoisier: (late 1700s)
- Law of Conservation of Mass & Law of Definite Proportions
(Ex. Water is always 11% hydrogen and 89% oxygen!)
- recognized and named oxygen and hydrogen
Proust: (1799)
- If a compound is broken down into its constituents, the products exist in the same ratio as in the compound.
- experimentally proved Lavoisier's laws.
Dalton: (early 1800s)
1. Elements are made of tiny particles called atoms.
2. All atoms of a given element are identical.
3. The atoms of a given element are different from those of another element.
4. Different atoms can combine together to form chemical compounds.
5. Atoms cannot be created, divided into smaller particles, nor destroyed.
J.J.Thomson:(1850s)
- raisin bun model (solid, positive spheres with negative particles embedded in them)
- first mentioned positive and negative charges
- discovered and demonstrated the existence of electrons
In 300 BC, Democritus, a Greek philosopher said atoms were indivisible particles.
- Law of Conservation of Mass & Law of Definite Proportions
(Ex. Water is always 11% hydrogen and 89% oxygen!)
- recognized and named oxygen and hydrogen
Proust: (1799)
- If a compound is broken down into its constituents, the products exist in the same ratio as in the compound.
- experimentally proved Lavoisier's laws.
Dalton: (early 1800s)
1. Elements are made of tiny particles called atoms.
2. All atoms of a given element are identical.
3. The atoms of a given element are different from those of another element.
4. Different atoms can combine together to form chemical compounds.
5. Atoms cannot be created, divided into smaller particles, nor destroyed.
J.J.Thomson:(1850s)
- raisin bun model (solid, positive spheres with negative particles embedded in them)- first mentioned positive and negative charges
- discovered and demonstrated the existence of electrons
Rutherford: (1905)
（atoms have a positive, dense center with electrons outside it）
- planetary model of the atom
Neils Bohr: (1885-1962)
- each energy level correspond to a different "orbit" of an electron around the atom
- the Bohr model & shell model of the atom
