Chemical Bonding

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Chemical Bonding
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How do elements know how to bond? Are there
rules/guidelines?

• What is a chemical bond?

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Bond Formation

• A n exchange of electrons between neighboring
  atoms to transferring or sharing electrons to
  become a more stable substance.

Bond Energy (energy needed to break a bond)
varies depending on the strength of this force of
attraction between atoms
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Where does bonding occur in the atom?
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Valence Electrons are involved in bonding
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Electron Distribution in Molecules

• Electron distribution is depicted with Lewis
  structures
• (electron dot diagrams)

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Review of Valence Electrons

• Periodic Table is a tool to find the number of
  valence electrons of a specific atom

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Lewis Dot Diagrams (Lewis Structures)
Valence electrons are indicated as single dots
circulating the chemical symbol.
(Chemical symbol represents the remaining core
electrons and nucleus)
Unpaired dots are potential bonding points for
the atom.
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• What are the rules/guidelines to make a bond?

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OCTET RULE

• Atoms will gain/lose/share electrons in an
  attempt to have 8 valence electrons (or O).
• Exception H and He

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How does it know if it should share or take to
make 8?
What type of bonding is each picture describing?
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Bonding Just the Facts

• Ionic Bonding
• Between a metal and a non-metal (Cation Anion)
• Neutral, balanced charge
• Gain or Lose valence e- to get an OCTET

• Covalent Bonding
• Between 2 non-metals
• NO ions
• Share valence e- to get the OCTET

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Electronegativity a rating scale indicating an
atoms ability to control electrons in a bond
Where are the control freaks located? Where are
the push-overs located? What type
of bonding occurs in the middle? What happened to
the noble gases?
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Electronegativity Difference

• Ionic Bonding
• END greater or equal to 1.7
• Covalent Bonding
• END less than 1.7

• EX NaCl
• EX BH3
• EX RbBr
• EX SO2

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Non-Polar Covalent Bonds
Polar Covalent Bonds

• Even Sharing

• Uneven Sharing

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How are properties of a substance dependent upon
chemical structure?
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Building an Crystalline Structure
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Lattice Structures3-dimensional structure of
crystals
allotropes of carbon - 6 min
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Building a Lewis Dot Structure

• HONC..1,2,3,4 or use periodic pattern

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Examples

• CH4 SF2
• NH3
  HBr
• CH3NH2 OH-1

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Polarity of a Structure

• Polarity uneven distribution of electrons
  around the central atom
• Effects attractiveness of one molecule to
  another
• Causes the following properties
• Solubility
• Melting Point and Boiling Point
• Viscosity
• Cohesion
• Evaporation Rate
• Density
• Surface Tension

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Water

• Water is POLAR because it has a positive end and
  a negative end. (difference in electronegativity)

What do you know about properties of water?
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Olive Oil
Very little attractiveness between particles
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• This is why oil and water will not mix! Oil is
  nonpolar, and water is polar.
• The two will repel each other, and so you can not
  dissolve one in the other
• lancaster lab - 100 min - hydrophobic coating

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Washing Clothes

• how soap works - 124 min

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Cell Wall Membrane
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How does the high polarity of water affect your
life?

• Bozeman Science - 830 min
• Solubility -
• Melting Point and Boiling Point
• Viscosity
• Cohesion
• Evaporation Rate
• Density
• Surface Tension

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MOLECULAR GEOMETRY
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MOLECULAR GEOMETRY

• VSEPR
• Valence Shell Electron Pair Repulsion theory.
• Most important factor in determining geometry is
  relative repulsion between electron pairs.

Molecule adopts the shape that minimizes the
electron pair repulsions.
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Bond and Lone Pairs

• Valence electrons are distributed as shared or
  BOND PAIRS and unshared or LONE PAIRS.

This is has 4 repulsion areas. (these are called
electron domains)
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Some Common Geometries
Tigonal Planar
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VSEPR charts

• Use the Lewis structure to determine the geometry
  of the molecule
• Charts use the CENTRAL atom for all data!
• Think REGIONS OF ELECTRON DENSITY rather than
  bonds (for instance, a double bond would only be
  1 region)

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Molecular Shapes (Valence Shell Electron Pair
Repulsion)
Total of Electron Domains
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Examples

• CH4 SF2
• NH3
  HBr
• CH3NH2 OH-1

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How does molecular structure effect my body?
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