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Laws to Know
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Conservation of Mass (matter)
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Matter is neither created nor destroyed, only
rearranged
Definite Proportions
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Compounds contain same elements with same
proportions (H2O is always 2H:1O)
Plum Pudding Model
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Early model of atomic structure
Dalton’s Atomic Theory
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Formed in early 1800’s
Some still used today
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Not all parts still considered true
Pg 66
Atomic theory
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Smallest unit that maintains properties of a
substance
All matter is composed of atoms
If atomic structure is changed, all chemical and
physical properties will change
Consist of 3 main subatomic particles
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Proton, electron, neutron
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These consist of elementary particles (quarks, leptons, gauge
bosons – list goes on an on: you do not need to know these)
Electron discovery
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Cathode Ray Tube (JJ Thomson 1897)
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Found mass-charge ratio of electrons
Cathode ray consist of a stream of negative
charges (electrons)
Flow from cathode (-) to the anode (+)
Degree of deflection led to the ratio
Example of Cathode Ray Tube
Mass of an electron
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Oil Drop Experiment (Millikan 1909)
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Found the charge of an electron
Combined with Thomson’s work, one can find the
mass of an electron
Atomizer used to spray fine mist of oil droplets
Used electric charge to suspend droplets
Example of Oil Drop
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http://animation.videosift.com/video/Oil-DropExperiment-Millikan
Nucleus Conclusions
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Gold Foil Experiment (Rutherford, Geiger,
Marsden 1911)
Fire alpha particles (He2+) at thin gold foil
Most pass through
Some have small angle deflection
Very few (1/8000) redirected back to the
source
Gold Foil Cont.
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Conclude that most of the atom is empty
space
Dense positive center called the nucleus
Most of the atoms mass found in the nucleus
Protons
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X-Ray Tube (Moseley 1914)
Determined the charge of the nucleus (# of
protons)
Assigned atomic number to most atoms
Beginning of periodic table being ordered off
atomic number (was atomic mass before)
Isotopes and Neutrons
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Each atom has a unique number of protons
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If number of protons are different, atom is
different
Atoms of the same element can have
different masses
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Difference caused by neutron
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Uncharged particle in the nucleus
Roughly the same mass as a proton
Determining Mass Number
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All isotopes have different mass number
Mass number is from Proton + Neutron
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Number of Protons do not change
Neutrons Can change
 6 N, 6P
14C  8N, 6P
 12C
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Mass of Protons, Neutrons, Electrons
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Proton = 1.67262158 x 10-27 kilograms
Neutron =1.67492729 x 10-27 kilograms
Electron = 9.10938188 × 10-31 kilograms
Proton and neutron have about same mass
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Near 1 atomic mass unit (amu)
Electron mass is nearly negligible in
comparison to protons and neutron
Average Atomic Mass
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Average taken of all natural isotopes
Some isotopes are more common than other
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Carbon-12, Oxygen-16, Hydrogen-1 etc
Average atomic mass will be near the most
prevalent isotope
Solve just like all average problems
Solving Average Atomic Mass
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Look page 80 table 3-4
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Based on atomic mass of the individual isotopes
Multiply percentage by mass
Add to get the total
Notice how mass number and atomic mass are
not exact
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Due to slight difference between protons and neutrons
And in formation of the nucleus some mass is lost as
energy
Ions
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Atoms that have gained or lost an electron
Those that gain electrons
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Negative charge
Nonmetals
Those that lose electrons
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Positive charge
Metals
Pure Substances
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All have fixed ratios
Element:
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Consist of only one type of atom
Compound
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Consist on 1 or more types of atoms
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Ionic: Metal and nonmetal
Molecular: 2 or more nonmetals
Metallic: 2 metals
Mixtures
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Do not have fixed ratios
Homogeneous (solution)
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Consist on only one phase
All parts have same physical/chemical properties
Heterogeneous
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May consist of multiple phases (not required)
Sections have different chemical/physical
properties