Section 2.2 Electrons in Atoms

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Section 2.2 Electrons in Atoms

• Objective
• Relate the electron to modern atomic theory.
• Compare electron energy levels in an atom.
• Illustrate valence electrons by Lewis electron
  dot structures.

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Electron Motion and Energy

• Opposites attract
• So, why are the negative electrons not pulled
  into the positive nucleus of an atom?

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Niels Bohr (1885-1962)

• A Danish scientist who worked the Rutherford
  solved this very question.
• He proposed the the electrons have enough energy
  to keep them in constant motion around the
  nucleus.
• He compared the motion of the electrons to the
  motion of the planets around the sun.

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Electromagnetic Spectrum

• Electromagnetic spectrum the whole range of
  electromagnetic radiation.
• Radio waves
• Microwaves
• Infrared rays
• UV rays
• X rays
• Gamma rays

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Electromagnetic Spectrum
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Electrons and Light

• When electrons of an atom are excited they emit
  light.
• Emission spectrum the spectrum of light
  released from excited atoms of an element.

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Emission Spectrum of Hydrogen
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Evidence for Energy Levels

• When electrons absorb energy, the only absorb the
  amount needed to move to a specific higher energy
  state.
• It is when the electrons fall back to the lower
  energy state that they emit only certain amounts
  of energy and therefore only certain colors of
  light.
• Because of this Bohr reasoned that electrons move
  around the nucleus only at distances that
  correspond with the those amounts of energy.
• These regions of space in which electrons can
  move around the nucleus of an atom are called
  energy levels.

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Energy Levels of Hydrogen
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The Electron Cloud Model

• Because of on going research scientists today
  realize that energy levels are not neat,
  planet-like orbits around he nucleus of an atom.
• They are spherical regions of space around the
  nucleus in which electrons are most likely to be
  found.

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Electron Cloud

• Electron Cloud The space around the nucleus of
  an atom where the atoms electrons are found.

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Electrons in Energy Levels

• The lowest energy level is the smallest and the
  closest to the nucleus.
• The first energy level holds a maximum of two
  electrons
• The second energy level hold a maximum of 8
  electrons
• The third energy level holds 18 electron
• You can use the formula 2n2 to determine how many
  electrons each level holds

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Valence Electrons

• Valence Electrons the electrons in the
  outermost energy level
• You can use the periodic table to determine how
  many valence electrons some elements have

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Valence Electrons

• Group 1 1 valence electron
• Group 2 2 valence electrons
• Group 13 3 valence electrons
• Group 14 4 valence electrons
• Group 15 5 valence electrons
• Group 16 6 valence electrons
• Group 17 7 valence electrons
• Group 18 8 valence electrons

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Valence Electrons

• Why is it important to know how many valence
  electrons an element has?
• It is the electrons of an atom that interact.
• Therefore, many of the chemical and physical
  properties of an element are directly related to
  the number and arrangement of valence electrons.

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Oxygen
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Lewis Dot Diagrams

• Lewis Dot Diagram a diagram where dots or other
  small symbols are placed around the chemical
  symbol of an element to illustrate the valence
  electron.

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Lewis Dot
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Lets Try It

• Oxygens Lewis Dot
• Carbons Lewis Dot
• Sodiums Lewis Dot