Atomic Structure

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• Chapter 4
• Atomic Structure

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History of Atom

• Democritus (2500 YEARS AGO) Greek philosopher
• Atmos uncut or indivisible
• Dalton (1800s) British Scientist
• Proposed the first Atomic Theory
• All elements are composed of atoms
• All atoms of the same element are the same
• Compounds contain atoms of more than one element
• In a compound, atoms combine in the same way

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History of Atom
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History of Atom

• J.J. Thompson (early 1900s)
• Cathode Ray Tube Experiment
• Discovered the first sub-atomic particle, the
  electron
• A particle smaller than the atom
• Has a negative charge
• Change Proposed the plum pudding model
• Milikan did the oil-drop experiment
• Determined the charge of the electron

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Thomsons Experiments
Figure 5
Cathode Ray Tube Experiment
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History of Atom

• Rutherford (1900s)
• Gold-foil experiment
• Alpha particles shot at a thin gold foil
• Particles were expected to go right through
• Some were deflected and even bounced back
• Conclusion there was a nucleus in the middle
  where the charge is found
• Model changed again

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The Gold Foil Experiment
Figure 5
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History of the Atom

• From Dalton to Rutherford

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A Scientific Method
Figure 12
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Structure of Atom

• Atomic number the number of protons found in
  the nucleus
• Unique to each element
• A whole number (count the of protons)
• Will be found on the periodic chart
• Mass number the number of protons AND neutrons
  in the nucleus.
• This will change because it can gain
  or lose neutrons
• of neutrons Mass - atomic

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1. 16 8 8
2. 32 16 16
3. 108 47 61
4. 80 35 45
5. 207 82 125

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Structure of Atom

• Isotopes Will have the same atomic number (
  of P)
• But different mass number
• This is because there will be more or less
  neutrons
• Isotopes are still neutral because the neutrons
  are neutral
• Atomic mass it the average mass of the commonly
  occurring isotopes.

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History of Atom

• Bohrs Model (1900s)
• He focused on the electrons
• Found that they had certain energy levels
• Proposed that the have fixed, specific orbits
• Change Orbit model
• Evidence for this gaining and releasing of
  energy from an atom

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History of Atom

• Schrodinger mathematician (1900s)
• Electron Cloud Model
• Found that they had certain energy levels
• Instead of fixed, specific orbits, there are
  orbitals
• Orbital is a proposed area where the electron is
  likely to be found
• Change Electron cloud model

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History of Atom

• Modern Theories Bohr Model to Electron Cloud
  Model

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Structure of Atom

• In the quantum mechanical model, the probability
  of finding an electron within a certain volume of
  space surrounding the nucleus can be represented
  as a fuzzy cloud. The cloud is more dense where
  the probability of finding the electron is high.

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• The propeller blade has the same probability of
  being anywhere in the blurry region, but you
  cannot tell its location at any instant. The
  electron cloud of an atom can be compared to a
  spinning airplane propeller.

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Reading Strategy
Section 4.3
Sequencing

• a. Electron moves to higher energy level.
• b. Electron moves to lower energy level.

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Number of Orbitals and Electrons in Energy Levels
Figure 15
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Structure of Atom

• Different atomic orbitals are denoted by letters.
  The s orbitals are spherical, and p orbitals are
  dumbbell-shaped.

These are probable locations where an electron is
most likely to be found.
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Structure of Atom

• Four of the five d orbitals have the same shape
  but different orientations in space.

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Reading Strategy
Section 4.1

• Summarizing

a. Dalton b. Indivisible, solid spheres c.
Thomson d. Negative charges evenly scattered
through a positively charged mass of matter
(plum pudding model) e. Deflection of alpha
particles passing through gold foil