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					Atoms, Elements and the
          Periodic Table
Periodic Table of
       Elements
Periodic Table
 The periodic table organizes the elements in a
  particular way. A great deal of information about an
  element can be gathered from its position in the
  period table.
 For example, you can predict with reasonably good
  accuracy the physical and chemical properties of the
  element. You can also predict what other elements a
  particular element will react with chemically.
 Understanding the organization and plan of the
  periodic table will help you obtain basic information
  about each of the 118 known elements.
Finding Data on Elements
Each square of the periodic table includes an element’s
atomic number, chemical symbol, name, and atomic mass.
What’s in a square?
 Different periodic tables
  can include various bits
  of information, but
  usually:
   atomic number
   symbol
   atomic mass
   number of valence
    electrons
   state of matter at room
    temperature.
Key to the Periodic Table
                   Elements are organized on
                    the table according to their
                    atomic number, usually
                    found near the top of the
                    square.
                     The atomic number refers
                       to how many protons an
                       atom of that element has.
                     For instance, hydrogen
                       has 1 proton, so it’s
                       atomic number is 1.
                     The atomic number is
                       unique to that element. No
                       two elements have the
                       same atomic number.
 Atomic Number

                               This refers to how
                                many protons an
                                atom of that element
                                has.
                               No two elements,
                                have the same
                                number of protons.

Bohr Model of Hydrogen Atom

                                        Wave Model
Atomic Mass

 Atomic Mass refers
  to the “weight” of
  the atom.
 It is determined by
  adding the number
  of protons to the
                            This is a Helium atom. Its
  number of neutrons.   H   atomic mass is 4.( 2 protons
                            and 2 neutrons)
                            What is it’s atomic mass?
Atomic Mass and Isotopes
                 While most atoms have
                  the same number of
                  protons and neutrons,
                  some don’t.
                 Some atoms have more
                  or less neutrons than
                  protons. These are called
                  isotopes.
                 An atomic mass number
                  with a decimal is the total
                  of the number of protons
                  plus the average number
                  of neutrons.
Isotopes
Atoms of all isotopes of carbon contain six protons, but they
differ in the number of neutrons. Carbon-12 is the most
common isotope.
Atomic Mass Unit (AMU)

                 The unit of
                  measurement for an
                  atom is an AMU. It
                  stands for atomic
                  mass unit.
                 One AMU is equal to
                  the mass of one
                  proton.
     Atomic Mass Unit (AMU)

 There are
  6 X 1023 or
 600,000,000,000,000,
 000,000,000 amus in
 one gram.
 (Remember that
  electrons are 2000
  times smaller than one
  amu).
Symbols

               All elements have

C   Carbon
                their own unique
                symbol.
               It can consist of a
                single capital letter,

Cu              or a capital letter
                and one or two
                lower case letters.
     Copper
    Valence Electrons
 The number of valence
  electrons an atom has
  may also appear in a
  square.
 Valence electrons are the
  electrons in the outer
  energy level of an atom.
 These are the electrons
  that are transferred or
  shared when atoms bond
  together.
   chlorine
                          nitrogen

     gold
                 silver
                       mercury
              oxygen             hydrogen
helium
                 sodium        niobium

 neodymium
                          carbon
    Mendeleev
 In 1869, Dmitri Ivanovitch Mendeléev
  created the first accepted version of
  the periodic table.
 He grouped elements according to
  their atomic mass, and as he did, he
  found that the families had similar
  chemical properties.
 Blank spaces were left open to add
  the new elements he predicted would
  occur.
                                  - Organizing the Elements


Organization of the Periodic Table
The 18 columns of the periodic table reflect a repeating
pattern of properties that generally occur across a period.
      History of Atomic Theory
      Democritus (from about 440 BC)

      coined the term atom which means uncuttable

      He felt that if you kept cutting matter smaller and smaller
       eventually you will no longer be able to cut any further.




20
                                 - Introduction to Atoms


Models of Atoms
For over two centuries, scientists have created models of
atoms in an effort to understand why matter behaves as it
does. As scientists have learned more, the model of the atom
has changed.
      John Dalton (1766-1844)
      Felt that an atom was indivisible

      spherical in shape

      Model: Sphere

      Analogy: Billiard ball




22
     JJ Thomson (1856-1940)
      Discovered electrons

      Felt that an atom was negatively charged particles
       floating in a positive soup

      Model: Charges floating around

      Analogy: Raisin bun or Plum Pudding




23
     Hantaro Nagaoka (1865-1950)
      Developed the planetary model of atom

      Model: Positive sphere with electrons orbiting in a ring

      Analogy: Saturn




24
      Ernest Rutherford (1871-1937)
      Discovered the nucleus, the proton and first split an
       atom

      Model: An atom was a small positively charged
       nucleus surrounded by electrons orbiting around it.

      Analogy: A beehive




25
     Rutherfords Famous Experiment
      Called the Gold Foil Experiment
       Alpha particles were fired at thin gold foil
       A detector encircled the foil and lit up when hit with alpha
        particles.
       If the plum pudding model were true it was expected most
        particles would go straight through the foil with only slight
        deflection.
       However, in the experiment, some particles were deflected
        back at a sharp angle proving the existence of a small,
        dense, and positively charged nucleus.




26
     Rutherfords results

                             Plum pudding expected
                             results. Particles go
                             through.

                           Text
                             Actual results. Some are
                             deflected back due to a
                             nucleus




27
     Another view of the experiment




28
29
           Niels Bohr
           Worked out details of atomic structure. Notably
            orbital layers. Solved problems related to
            Rutherfords model.

           Model: Electrons orbit in rings at different
            distances from the nucleus.

           Analogy: Planets orbiting the sun




     29
     Erwin Schroedinger (1887-1961)
      Major discoveries in quantum mechanics. Nature of
       electrons in atoms.

      Model: Electrons exist in a probability distribution around
       the atom. Kind of like a cloud.

      Analogy: A spinning fan blade.




30
                                - Introduction to Atoms


Structure of an Atom
A carbon atom consists of protons and neutrons in a
nucleus that is surrounded by electrons.
     Quick Quiz: Historical Atom
 1. What did Dalton say an atom was like?
 1. A billiard ball, or a pool table ball
 2. What did JJ Thomson say an atom was like?
 2. Raisin bun
 3. What did Rutherford say an atom was like?
 3. A beehive
 4. What are the 3 parts of an atom?
 4. Proton, Neutron, Electron




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