Chemical
Bonding
How do elements “know” how to bond?
Are there rules/guidelines?
 What is a chemical bond?
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
Where does
bonding occur in
the atom?
Valence Electrons
are involved in
bonding
Electron
Distribution
in Molecules
 Electron distribution is depicted
with Lewis
structures
(electron dot diagrams)
G. N. Lewis
1875 - 1946
Review of Valence Electrons
Periodic Table is a tool to find the
number of valence electrons of a
specific atom
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.
What are the rules/guidelines to
make a bond?
OCTET RULE
 Atoms will
gain/lose/share electrons in an attempt
to have 8 valence electrons (or O).
 Exception: H and He
How does it “know” if it should
share or take to make 8?
What type of bonding is each picture describing?
Bonding: Just the Facts
 Ionic Bonding
 Covalent Bonding
 Between a metal and a non-
 Between 2 non-metals
metal (Cation + Anion)
 Neutral, balanced charge
 Gain or Lose valence e- to get
an OCTET
 NO ions
 Share valence e- to get the
OCTET
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?
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
Polar Covalent
Bonds
- Uneven Sharing
Non-Polar
Covalent Bonds
•
Even Sharing
How are properties of a substance dependent upon
chemical structure?
Building an Crystalline Structure
Lattice Structures
3-dimensional structure of crystals
allotropes of carbon
Building a Lewis Dot
Structure
•HONC…..1,2,3,4 or
use periodic pattern
Examples
• CH4
SF2
• NH3
HBr
• CH3NH2
OH-1
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
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?
Olive Oil
Very little attractiveness between particles
 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 - 1:00 min - hydrophobic coating
Washing Clothes
 how soap works - 1:24 min
Cell Wall
Membrane
How does the high polarity of
water affect your life?
 Bozeman Science - 8:30 min
 Solubility  Melting Point and Boiling Point
 Viscosity
 Cohesion
 Evaporation Rate
 Density
 Surface Tension
MOLECULAR
GEOMETRY
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.
Bond and Lone Pairs
 Valence electrons are distributed
as shared or BOND PAIRS and
unshared or LONE PAIRS.
••
H
Cl
•
•
••
shared or
bond pair
lone pair (LP)
This is has 4 repulsion areas.
(these are called electron domains)
Some Common
Geometries
Tigonal Planar
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)
Molecular Shapes
(Valence Shell Electron Pair Repulsion)
Examples
• CH4
SF2
• NH3
HBr
• CH3NH2
OH-1
How does molecular structure
effect my body?
Smell Receptors
Enzymes -
Video; 5 min. Ameoba Sisters
Video: 6 min . Digestive Enzymes
Video: 4 min Real life Enzymes