atomic theory of matter - developed by John Dalton  

• all elements are composed of atoms
• atoms in each element are identical
• chemical reactions can't change, create, or destroy atoms
• compounds are combinations of atoms
• atoms - smallest particles of an element that still contain all the characteristics of that element
• law of constant composition - kinds of atoms and their ratios are constant in compounds
• law of conservation of mass - total mass after a reaction is equal to total mass before the reaction
• law of multiple proportions - atoms combine in compounds in simple ratios

cathode ray tubes - vacuum tube through which high voltage creates radiation  

• produce rays that cause glass to fluoresce, give off light
• electrons move from the cathode (-) to the anode (+)
• J. J. Thomson - summarized his cathode ray observations and found the electron's electrical charge to be 1.76 x 108 coulombs per gram
• Robert Millikan - used his "oil-drop" experiment to calculate the mass of the electron by using his measurements of the charge in a single electron and Thomson's calculations

radioactivity - spontaneous emission of radiation  

• Ernest Rutherford - aka "the second Newton"; discovered the 3 types of radiation
• alpha radiation - positive charge, more massive than beta; equal to nuclei of helium
• beta radiation - negative charge, less massive than alpha; equal to high speed electrons/cathode rays
• gamma radiation - unaffected by electrical fields, has no charge

nuclear atom - final view of atom discovered by Rutherford  

• J. J. Thomson - believed that electrons were embedded in a positively charged sphere
• Ernest Rutherford - used gold foil experiment to prove that positive charge resided in a very small, dense region called the nucleus
• protons discovered by Rutherford in 1919
• neutrons discovered by James Chadwick in 1932