# Unit 2 Chapter 3: Atomic Theory

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15 Terms
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Democritus (400BCE)
-believed that eventually matter would not be able to be split anymore -coined term "atom" from atomus, meaning indivisible
Aristotle (400BCE)
-believed the world was continuous and made up of earth, air, fire, water
Dalton (1808)
Dalton's Atomic Theory
JJ Thomson (1897)
credited with discovering the negative particle of the atom: electron
Millikan (1909)
measured the charge of the electron, only american mentioned
Rutherford (1911)
gold foil experiment - founded the details of the atom's structure - nucleus
Discovery of the Three Laws (1790)
1. Conservation of Mass 2. Definite Proportion 3. Multiple Proportions
Atomic Theory
1. all matter is made of atoms 2. atoms combine in whole number ratios 3. atoms of the same element share size, mass, etc; vice-versa for different elements 4. atoms are indivisible and indestructible (false) 5. compounds are formed by a combination of different kinds of atoms (false)
Law of Conservation of Mass
-mass stays the same before and after chemical reaction -mass is neither created nor destroyed -there must be equal amounts of reactants and products
average atomic mass
the weighted average of the atomic masses of the natural isotopes of an element
mole
a counting number; it is the amount of substance that contains as many particles as there are atoms in exactly 12g of Carbon-12
molar mass
mass of one mole of a pure substance (g/mol)
conversion chart
molar mass = 1 mole = 6.022x10^23
how to find avg atomic mass
mass (amu) x abundance (%) total / 100