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Chemical Bonding

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Chemical Bonding Molecular Shapes (Valence Shell Electron Pair Repulsion) Examples CH4 SF2 NH3 ... – PowerPoint PPT presentation

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Title: Chemical Bonding


1
Chemical Bonding
2
How do elements know how to bond? Are there
rules/guidelines?
  • What is a chemical bond?

3
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
4
Where does bonding occur in the atom?
5
Valence Electrons are involved in bonding
6
Electron Distribution in Molecules
  • Electron distribution is depicted with Lewis
    structures
  • (electron dot diagrams)

7
Review of Valence Electrons
  • Periodic Table is a tool to find the number of
    valence electrons of a specific atom

8
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.
9
  • What are the rules/guidelines to make a bond?

10
OCTET RULE
  • Atoms will gain/lose/share electrons in an
    attempt to have 8 valence electrons (or O).
  • Exception H and He

11
How does it know if it should share or take to
make 8?
What type of bonding is each picture describing?
12
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

13
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?
14
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

15
Non-Polar Covalent Bonds
Polar Covalent Bonds
  • Even Sharing
  • Uneven Sharing

16
How are properties of a substance dependent upon
chemical structure?
17
Building an Crystalline Structure
18
Lattice Structures3-dimensional structure of
crystals
allotropes of carbon - 6 min
19
Building a Lewis Dot Structure
  • HONC..1,2,3,4 or use periodic pattern

20
Examples
  • CH4 SF2
  • NH3
    HBr
  • CH3NH2 OH-1

21
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22
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

23
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?
24
Olive Oil
Very little attractiveness between particles
25
  • 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

26
Washing Clothes
  • how soap works - 124 min

27
Cell Wall Membrane
28
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

29
MOLECULAR GEOMETRY
30
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.
31
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)
32
Some Common Geometries
Tigonal Planar
33
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)

34
Molecular Shapes (Valence Shell Electron Pair
Repulsion)
Total of Electron Domains
35
Examples
  • CH4 SF2
  • NH3
    HBr
  • CH3NH2 OH-1

36
How does molecular structure effect my body?
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