Atomic Theory!

Timeline of Atomic Theory

Early Atomic Theory

• Greeks were the first to mention the atom (atomos)
• 300 BCE Democritus sated that atoms were invisible particles
• Not a testable theory, only a conceptual model
• No mention of any nucleus or its constituents
• Can't be used to explain chem reactions
• Most accepted view for over 2000 years

Lavoisier (late 1700s)

• Created the of masslaw of conservation
• Created the law of definite proportions
• Doesn't discuss what atoms were or how they were arranged
  

Proust (1799)

• If a compound is broken down into its constituents products will exist in the same ration as in compound
• Proved Lavoisier's laws

Dalton (early 1800s)

• Atoms = solid, indestructible spheres
• Provides for different elements
• Doesn't mention subatomic particles
• Can't explain isotopes
• No mention of nucleus

J.J Thompson (1850s)

• Raisin bun model
• Solid, positive spheres, with negative particles embedded in them
• 1st atomic theory to have positive (protons) and negative (electrons) charges
• Intro to the idea of nucleus
• No mention of neutrons, radioactive decay can`t be explained
• No mention of chemical bonding
  

Rutherford (1905)

• Showed atoms have positive, dense center with electrons outide it
• Resulted in planetary model
• Explains why electrons spin around nucleus
• Suggests atoms mostly empty space
• Should be unstable (electrons and protons attract=destroy atom)
• No mention of neutrons
• Doesn`t explain valance level electrons role in chem bonds

Bohr (1920s)

• Electrons must only exist in specific orbitals around nucleus
• Explains how valance electrons are involved in bonding
• Explains difference between ionic and covalent bonding
• Resolves problem of atomic instability
• Includes neutron (discovered in 1932)
• Explains atomic emission spectra