Chemistry: History of Atoms

Dalton's Atomic Theory

1. Atoms can combine to form compounds

2. Chemical reactions change compositions but never change atoms

3. Atoms of different elements vary in size and mass

Dalton's Model

A solid sphere of matter that was uniform throughout (Billiard ball model)

Thomson's Theory

1. Proposed the electrical nature of the atom discovered the electron

2. Atom is mostly positive charge by mass with electrons scattered throughout

Thomson's Model

"blueberry muffin" experiment (disapprove Dalton's theories)

Millikan

Determined the charge & mass of electrons with his oil drop experiment

Rutherford

1. Discovered nucleus with his "nuclear" atom experiment (Gold foil experiment)

2. Positive charges in densely packed nucleus with electrons around the nucleus (protons)

3. Most of the atoms is empty space

Chadwick

Discovered a neutral particle in the nucleus (neutron)

Bohr

Electrons orbit around the nucleus

Today's theory

1. Electron cloud distribution

2. Electrons exist in dense clouds surrounding the nucleus

Proton

Symbol: p+

Charge: 1 amu

Where?: Nucleus

Function Identify

Neutron

Symbol n°

Charge: 1 amu

Where? Nucleus

Function: Add mass

Electron

Symbol: e-

Charge: 1/2000 amu

Where?: Outside nucleus

Function: Reactions (rxns)