Investigating Atoms and Atomic Theory

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Bohr Model

• In 1913, the Danish scientist Niels Bohr proposed
  an improvement. In his model, he placed each
  electron in a specific energy level.

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• In 1912, Niels Bohr determined that e- are
  restricted to certain energy levels that surround
  the nucleus like orbits. (This was later
  modified by Schrödinger.)
• He also determined that e- move between these
  energy levels.

Step 2 The e- falls back to the 1st energy
level and emits a photon of the same color as the
photon that it absorbed.
Step 1 An e- absorbs a photon and jumps up to
a higher energy level
Nucleus
1st energy level
2nd energy level
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Atomic Models

• This model of the atom may look familiar to you.
  This is the Bohr model. In this model, the
  nucleus is orbited by electrons, which are in
  different energy levels.
• A model uses familiar ideas to explain unfamiliar
  facts observed in nature.
• A model can be changed as new information is
  collected.

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Bohr Model

• According to Bohrs atomic model, electrons move
  in definite orbits around the nucleus, much like
  planets circle the sun. These orbits, or energy
  levels, are located at certain distances from the
  nucleus.

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Wave Model
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The Wave Model

• Todays atomic model is based on the principles
  of wave mechanics.
• According to the theory of wave mechanics,
  electrons do not move about an atom in a definite
  path, like the planets around the sun.

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The Wave Model

• In fact, it is impossible to determine the exact
  location of an electron. The probable location of
  an electron is based on how much energy the
  electron has.
• According to the modern atomic model, at atom has
  a small positively charged nucleus surrounded by
  a large region in which there are enough
  electrons to make an atom neutral.

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Electron Cloud

• A space in which electrons are likely to be
  found.
• Electrons whirl about the nucleus billions of
  times in one second
• They are not moving around in random patterns.
• Location of electrons depends upon how much
  energy the electron has.

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Electron Cloud

• Depending on their energy they are locked into a
  certain area in the cloud.
• Electrons with the lowest energy are found in the
  energy level closest to the nucleus
• Electrons with the highest energy are found in
  the outermost energy levels, farther from the
  nucleus.

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10.4 Electron Energy Levels

• Each energy level has a maximum number of e- it
  can hold
• 1st energy level holds 2 e-
• 2nd energy level holds 8 more e-
• 3rd holds 8 more e-
• 4th 18 more e-
• 5th 18 more e-
• 6th 32 more e-
• 7th 32 more e-

• Lower energy levels (closest to nucleus) are
  filled first.
• Each new row of the periodic table represents the
  beginning of a new energy level.

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Electron Structures of Atoms
nucleus
1st energy level
1st Period Hydrogen (1) Helium (2)
2nd energy level
2nd Period Lithium (3) Neon (10)
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