Brief History of Electricity

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Chapter 3
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Brief History of Electricity
1. Ancient Greeks discovered that if a piece of
amber were rubbed with fur- pieces attracted each
other. Later attributed to opposite charges (
and -) called static electricity
2. Benjamin Franklin mid 1700s showed that
lightning was a form of static electricity
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Alessandro Volta 1800 First battery
G. Johnstone Stoney 1874 coined the word
electron for the basic unit of electricity
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By the end of the 19th Century scientists had
discovered that the atom was not solid and
indivisible as Dalton had proposed. Several
important experiments led to these discoveries.
Lets look at 2 of them
1. J.J. Thompson and the Crookes Tube Experiment
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A) Led to discovery of electrons as basic unit of
negative charge, found randomly inside atom.
Cathode Rays are electrons
B) Plum-Pudding Model of the atom
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2. Ernest Rutherford and discovery of the nuclear
atom
A) Natural radioactivity 3 types alpha
particles (?), beta particles (?) and gamma
radiation (?)
B) Gold foil Experiment
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Electrons make up only about 1 of the total mass
of the atom
C) Nuclear Model of the atom
atom
Nucleus positive charge very
densevery small(less than 1 of the entire space
in the atom) but contains almost all the mass of
the atom
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C) Nuclear Model of the atom
First model
After discovery of neutrons
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Summary of particles inside atom Particle Symbo
l Location Relative Charge Relative
Mass (Mass ) Electron e- Outside
nucleus - 1 0.005 0 Proton p Inside
nucleus 1 1.000 Neutron n0 Inside
nucleus 0 1.000
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Atomic Number (Z) The number of protons in an
atom. Also the number of electrons in a neutral
atom. Unique for each element. Identifies the
element.
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• Mass Number The number of protons the
  number of neutrons in an atom. For example An
  atom with 5 protons and 7 neutrons
• Mass 5p 7n0 12
• This number is not unique for each element. All
  but one element have atoms with different numbers
  of neutrons and therefore different mass numbers.
  
• For example, there are 3 different atoms of C
  found in Nature, all having 6 protons, but one
  having 6 neutrons, one 7 neutrons and one with 8
  neutrons. What are their Mass Numbers?
• These 3 atoms are called isotopes of C. Isotopes
  are atoms of the same element with different Mass
  Numbers.
• Isotopic Symbols -

Mass
Atomic
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• Atomic Weight (AW) or better Atomic Mass The
  relative weight of an average atom of one element
  compared to that of another atom chosen to be the
  standard.
• The modern standard is the C-12 isotope
  (arbitrarily assigned a value of 12.0000 amu
  (atomic mass unit). Actually the AW of an
  element is the average (taking into account the
  relative amount of each) mass of all the
  naturally found isotopes.
• This is the non-whole found under each element
  in the Periodic Table.

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Niels Bohr Danish - 1912
Bohr Model Also called Solar System Model.
Nucleus with electrons revolving around in orbits
of specific energies (called Energy levels)
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• Each successive orbit has a maximum of
  electrons that can exist (2, 8, 18, 32, 50 etc)
  We will only worry about the first 20 elements.
  For these the maximum of electrons is 2 for the
  first and 8 for the rest (actually 18 in the
  third, but the last 10 are not important for us
  in this course).
• For every atom the electrons fill up the orbits
  in order beginning with the lowest energy. The
  closer to the nucleus, the lower the energy. In
  other words Li has an atomic of 3, therefore 3
  electrons (2 in the first level and 1 in the
  next).

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• See the following table. The electrons in the
  outermost energy level are called Valence
  electrons and that level is called the Valence
  Shell.

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Dimitri Mendeleev and the Periodic Table
Modern Version

• Names of Families
• Metals, Non-metals and metalloidsand Noble
  Gases
• Representative elements and transition metals

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1. Metals Left side - a) Properties Shiny,
malleable, ductile, conduct electricity heat
2. Non-Metals Right Side b) Properties
Brittle as solids, non-conductors
3. Metalloids In between c) Properties
Some of both metals non-metals
4. Noble Gases Far Right Column d)
Properties All are gases even at very low
temperatures, non-conductors, very little
tendency to chemically react
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Representative Elements Those in columns headed
by an A (IA, IIA etc). We will spend most of our
time dealing with these elements.
Transition Metals Those in columns headed by a
B.
Inner Transition Elements Bottom 2 rows