The Structure of Matter

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The Structure of Matter

• Atomic Models
• Subatomic Particles
• Forces Within the Atom

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Part One Atomic models past and present
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Atomic Models Throughout History

• Greek (400 BC)
• Dalton (1800)
• Thomson (1897)
• Rutherford (1908)
• Bohr (1913)
• Wave Model

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Greek (400 BC)

• Atomos indivisible
• Democritus said the smallest piece of matter was
  an atom
• Theory wasnt accepted for 2100 years

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Dalton (1800)

• All elements are composed of atoms. Atoms are
  indivisible and indestructible
• Atoms of the same element are exactly alike
• Atoms of different elements are different
• Compounds are formed by the joining of atoms of
  two or more elements

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Thomson (1897)

• Discovered negatively charged particles
• The atom was divisible!
• Particles discovered are electrons
• Plum Pudding Model
• Atom consists of positively charged material with
  negative charges spread evenly throughout

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Heres JJ!
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Rutherford (1908)

• Gold Foil Experiment
• Positive particles shot at gold foil occasionally
  bounced back!
• Proposed dense, positively charged center called
  the nucleus

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Thomsons theory
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Rutherfords reality
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Rutherfords atom
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Bohr (1913)

• Electrons move in definite orbits around the
  nucleus
• Places each electron in a specific energy level

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The Bohr Atom
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Wave Model

• Modern model based on wave mechanics
• Nucleus is surrounded by electrons
• Electrons do not move in orbits
• We can determine the probable location of an
  electron based on the amount of energy the
  electron has
• This probable location is called an orbital

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Part Two Subatomic particles
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Three main subatomic particles

• Proton
• Neutron
• Electron

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Protons

• Positively charged
• Found in nucleus
• Has a mass of 1 amu
• The number of protons determines the identity of
  the atom
• The atomic number tells the number of protons

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Elements are made of atoms
Hydrogen-1proton
Helium-2 protons
Lithium-3 protons
The number of protons determines the identity
of the element!! (atomic number)
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What is that other particle found in the nucleus?

• Its a neutron!
• Neutrons have no charge
• (theyre neutral)
• Neutrons have a mass of 1 amu
• Proton neutron mass number

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Electrons

• Electrons hang out in orbitals outside the
  nucleus of the atom
• Electrons have almost no mass
• The electron cloud is the majority of the volume
  of the atom
• ELECTRONS ARE NEGATIVELY CHARGED!

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More electron info!

• In a neutral atom, the number of electrons is
  equal to the number of protons
• When an atom gains or loses electrons, it is
  called an ion.

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The ionization process
Now Im a happy ion! Im POSITIVE! And my outer
shell is full, without that troublesome extra
electron.
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This chloride ion has added an electron. It is a
NEGATIVE ion! (note the inner 2 electrons are
not shown)
Now Im a happy ion!!!
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Sodium chloride-everybodys happy!
One lost
One gained.
(positive ion)
(negative ion)
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Quick Review

• The three subatomic particles are proton, neutron
  and electron
• Protons are positively charged, electrons are
  negative, neutrons are neutral
• When an electron is lost or gained, the atom
  becomes an ion.

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Isotopes

• Atoms with the same number of protons but
  different numbers of neutrons are called
  isotopes.
• Isotopes are designated by the symbol and the
  mass number
• H-1 1 proton, no neutrons
• H-2 1 proton, one neutron
• H-3 1 proton, two neutrons

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Its the Isotopes!
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What symbols represent ions?

• Elements on the left side of the periodic table
  will lose electrons to become positive ions
• Examples Ca2, Na,Fe3,Fe2,Al3
• Elements on the right side of the periodic table
  will gain electrons to become negative ions
• Examples F-, O2-, P3-, Cl-

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How big is the nucleus?

• If an atom was as big as a football field, the
  electrons would move over the entire field, while
  the nucleus would be the size of a lima bean in
  the middle of the field.

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If an atom was an elephant, the nucleus would be
as big as a flea on the elephant
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How massive is the nucleus?

• Even though the nucleus is VERY small, it is VERY
  massive. Even though its the size of the flea,
  it would weigh as much as the elephant. And
  though the electrons take up as much space as the
  elephant, they would only weigh as much as the
  flea.

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End of Part 2
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Part Three Forces Within The Atom
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Forces that govern the behavior of subatomic
particles

• Strong
• Weak
• Electromagnetic
• Gravity

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Strong force

• Opposes electro-
• magnetic force of
• repulsion between protons
• Glues protons together to form the nucleus
• Greatest of the forces, but has very limited range

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Weak force

• Responsible for radioactive decay in the atom

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Electromagnetic force

• Repels positively charged protons within the
  nucleus.
• Do you remember the force which holds them
  together so the atom doesnt explode?
• (Yes- strong force!)

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Electromagnetic force causes proton repulsion
Strong force overcomes electromagnetic
repulsion
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Gravity

• Weakest of the forces
• Force of attraction between all objects
• Effect seen easily only for very large objects

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Uses of the forces
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THE END