Atoms

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					Atoms
         Dalton’s Atomic Theory
                  1803

1) All matter is
  composed of
  extremely small
  particles called atoms
         Dalton’s Atomic Theory
                  1803

2) Atoms of one
   element are all alike

  (size, mass)
         Dalton’s Atomic Theory
                  1803

3) Atoms can’t be
    created, destroyed
    or subdivided
        Dalton’s Atomic Theory
                 1803

4) Atoms of different elements combine in
   simple whole number ratios to form
    compounds
        Dalton’s Atomic Theory
                 1803

5) In a chemical
   reaction, atoms are
   combined,
   separated, or
   rearranged
Conservation of mass
in chemical reactions
Conservation of mass
in chemical reactions
                 1897

The electron is discovered….
Rutherford’s Gold Foil Experiment
              1909


Ernst Rutherford bombards a piece of gold
foil with positively charged alpha particles
(the nucleus of a helium atom)
Some alpha particles
bounce back
 Rutherford’s Gold Foil Experiment
Observations:

1. Most of the alpha particles passed
   straight through the gold foil as if it
   wasn’t even there!
2. The nucleus of the atom is small, dense,
   and positively charged
 Rutherford’s Gold Foil Experiment
Interpretation (conclusions):

1. Atoms are mostly empty space and
   therefore MATTER is mostly empty
   space

2. Atoms have a small, dense, positively
   charged nucleus
            +
                         +
    +
                         This alpha particle
                         passes through the atom’s
+       +       +        empty space




                    Alpha particles have + charge
                    two + charges will repel each other
Subatomic Particles
    (Table O)

              Proton




                       Electron



             Neutron
                Protons
• Located in the atom’s nucleus

• Positive charge   +1

• Mass = 1 amu (Atomic Mass Unit)
                Neutrons
• Located in the atom’s nucleus

• zero charge   (neutral)

• Mass = 1 amu (Atomic Mass Unit)
                Electrons
• Located in the electron cloud outside the
  nucleus

• Negative charge    -1

• Mass = 1/1836 amu (negligible)
What are the subatomic particles in
       lithium and carbon?
Models of the atom
  A model of the atom to scale
• If YOU are the nucleus of an atom, your
  closest electron would be….



• ……..in downtown Rhinebeck!
Actual image of 2 atoms

				
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