Atomic Theory Flashcards
Democritus and Aristotle 420 BCE
Suggested that matter could be broken down into smaller and smaller components and coined “atoms” (invisible)
Law of Conservation of Mass
Mass is neither created nor destroyed
Law of Definite Proportions
A given compound has the same elements in the same proportions by mass regardless of the size of the sample or the source of the compound
Law of Multiple Proportions
If two or more different compounds are composed of the same two elements, then the ratio of their masses is always a ratio of small whole numbers
Lavoisier 1789
(Father of modern chemistry) law of conservation of mass
Proust 1798
Law of definite proportions
Dalton 1804 (law)
Law of multiple proportions
Dalton 1810
Published ideas of atomic theory, explaining that atoms were the smallest particles
Also: structure, properties of atoms and compounds, and mass, energy, and volume relationships of atoms
Summary of Atomic Theory
All matter is made of atoms, only atoms of the same element are chemically alike, definite, unique average mass of atoms of an element, not subdivided in chemical reactions
Empedocles 450 BCE
Avatar elements
Electron
Mass=9.1x10^-28 g
Radius=10^-5 angstrom
J. J. Thomson 1897
Discovered electrons from flow of electricity using cathode rays
Robert Millikan 1909
Additional experiments and mass of electrons
Angstrom
SI measure of length; 1 angstrom=10^-10 m
Proton
Mass=1.67x10^-24g
Radius is smaller than an electron
Eugen Goldstein early 1900s
Positive Ray research led to discovery of proton
Ernest Rutherford 1910
Credit for discovering the proton (gold foil experiment)
Neutron
Mass=1.67x10^-24g
Radius is smaller than electron
James Chadwick 1932
Discovery of neutrons
Nucleus Size
10^-4 angstrom, compared to atom size of 1-5 angstrom
William Thomson (Lord Kelvin) 1903
Plum pudding model
Neils Bohr 1913
Planetary model, then later beehive/electron cloud model
AMU
Atomic mass unit, based on carbon-12=12 scale, arbitrary assignment of value
Avogadro’s Number
Number of atoms found in one amu of an element, 6.02x10^23 atoms
Significant Figures
+ & - : least significant place
X & / : smallest number’s number of sig figs
