SOL CH'2a,c

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ATOMIC STRUCTURE

• SOL CH.2a,c

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ATOMIC STRUCTURE

• Atoms- smallest particle of an element that
  maintains the chemical identity of that element.
• Conservation of Matter -Antoine Lavoisier)
• Law of Constant Composition (Law of Definite
  Composition) - 1799 Joseph Louis Proust
• A given compound will always contain the same
  elements in the same proportions by mass.

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Daltons Atomic Theory of Matter 1803

• Theory based on five postulates
• All matter is composed of extremely small
  particles called atoms.
• Atoms of a given element are identicals atoms of
  different elements are different.
• Atoms cant be subdivided, created nor destroyed.
• Atoms of different elements combine in simple
  whole number ratios to form chemical compounds.
• In chemical reactions, atoms are combined,
  separated, or rearranged.

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Exceptions to the Atomic Theory

• Atoms are divisible
• Atoms of a given element can have a different
  mass (isotopes).

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Discovering Atomic Structure
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Cathode Ray Tube

• Cathode -negatively charged electrode
• Anode -positively charged electrode
• Cathode ray -ALWAYS flows from cathode to anode
  (from negative to positive electrode)
• Paddle wheel placed between electrodes ALWAYS
  turned toward the anode.
• Cathode ray composed of negative particles called
  -electrons

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Radioactive -spontaneous emission of radiation
from an element

• Chemical properties of a radioactive element
  changes as it gives off radiation.
• When radiation passes through electrically
  charged plates it splits to produce
• Alpha particles -positive charged
• Gamma particles -no charge
• Beta particles -negative charge

Since atoms are electrically neutral they must
contain a positive charge to balance negative
charge of electron
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Alpha Scattering Experiment

• Only small fraction of particles were deflected
  from foil.
• Other particles scattered all over the place.
• Most of the atom is empty space.
• Nucleus -positively charged small core of the
  atom that contains most of the atoms mass.

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Subatomic Particle Information
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• Atomic number (Z) - number of protons in an atom.
• each element has a unique number of protons.
• of protons used to determine the elements
  identity.
• Atoms are electrically neutral because of
  protons ( charged) of electrons (- charged)
• However, when an atom gains or loses electrons
  an ION is produced.
• Ions can have a positive charge (cation) or
  negative charge (anion).
• To determine the ion charge use the following
  equation
• charge of ion of protons - of electrons.

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• Mass number -total of protons and neutrons in
  an isotope.
• Used to help identify isotopes better.
• Isotopes -atoms that have the same of protons
  but a different number of neutrons.
• Hydrogen has three different isotopes. Each
  isotope has the same of protons (1) but a
  different neutrons Protium has 0 neutrons,
  deutrium has 1 neutron, and tritium has 2
  neutrons.

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Nuclear Symbols
Mass
2
1H
Atomic
Element Symbol
OR
Hydrogen-2
Mass
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• Atomic Mass Unit (u or amu) -
• 1 amu 1/12 the mass of a C-12 atom or 1 amu
  1.6605402 x 10-24g.
• Why should mass of atoms be converted to amu?
• - actual mass of oxygen atom is 2.657 x 10-23
  g. This number is not convenient to work with
  because it is too small.

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If the actual mass of an oxygen atom is why is
the mass on the periodic table 2.657X10-23 g
approximately 16? 2.657X10-23 g 1amu
16.006 amu 1.66
x 10 -24 g
Since most atoms, like oxygen, have isotopes each
isotope will have a different amu. The mass
displayed on the periodic table is an average
atomic mass (weighted average) of all the
isotopes for the atom.
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How to calculate average atomic mass
Chlorine element has two isotopes chlorine-35
and chlorine-37. How is the average atomic mass
determined. To do this two pieces of information
are needed and they are the fractional (natural)
abundance and the amu. Step 1 Convert the
fractional abundance of each
isotope,for the element, to a decimal
fraction. Chlorine -35 has a fractional abundance
of 75.53 Chlorine -37 has a fractional abundance
of 24.47 75.53 .7553 and 24.47
.2447 100 100
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How to calculate average atomic mass
Step 2 Multiply the atomic mass unit of the
isotope by the appropriate decimal
fraction. (34.969 amu x 0.7553) 26.4120857
amu (36.966 amu x 0.2447) 9.0455802 amu Step
3 Add the results. 26.4120857 amu 9.0455802
amu 35.4576659 or 34.457 amu
(mass displayed on periodic table)
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Nuclear Stability

• SOL CH. 2b

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Changes in the Nucleus
Chemical reactions atoms interact through their
electrons only. Nuclear reactions are not the
same. These reactions occur when the nucleus
changes. When the nucleus changes alpha,
beta, and gamma radiation are emitted. Alpha
beta particles are emitted from the nucleus.
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What causes Nuclear Stability?

• When more than one proton is present in the
  nucleus a repulsion force is present.
• The neutrons in the nucleus keep the nucleus
  intact by acting as a glue (nuclear force).
• As the of protons increase eventually the of
  neutrons are unable to override the force of
  repulsion and the nucleus becomes unstable.
• Elements with atomic of 84 and higher are
  radioactive.
• As the nucleus becomes unstable radiation is
  emitted.

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Three types of radiation
http//www.creation-science-prophecy.com/intro-ato
mic.htm
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Penetrating Power
www.deq.state.id.us/.../images/alpha_beta.jpg
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http//www.creation-science-prophecy.com/intro-ato
mic.htm
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Half-life
Half-life is the amount of time it takes for half
of a sample to decay.