chemical bonding and molecular structure chapter 12 sec 12.1 - 12.7 chapter 12 sec 12.1 - 12.7
TRANSCRIPT
Chemical Bondingand Molecular
StructureChapter 12
Sec 12.1 - 12.7
Review…
• Chemical bonds involve electrons
• Specifically, valence electrons (outer s and p orbitals)
• These electrons are transferred or shared in a molecule
Using Electronegativity:
• Large ∆EN = Ionic bond
• Medium ∆EN = Polar Covalent bond
• Small ∆EN = Non-polar Covalent bond
• Distance between location of elements on Periodic Table corresponds closely with ∆EN.
Polarity
Bonds (and molecules) are
“polar” if there is an unequal sharing of
electrons
Means “Partial Charge”
• A - indicates a partial negative charge (near the more electronegative atom
• While + is a partial positive charge
Compare Types of Bonds
KEY CONCEPT!
By transferring or sharing valence electrons…
ALL bonds allow the atoms in a compound to achieve a
“NOBLE GAS ELECTRON CONFIGURATION”
Lewis Structures
• Provide a way to illustrate valence electrons in a molecule
• Allow the prediction of Molecular Geometry and Molecular Polarity
Lewis Structures - Main Group Elements
Rules for Drawing Lewis Structures:
1. Find the sum of all valence electrons of atoms in the molecule
2. Use a pair of electrons to represent a bond between two atoms
3. Rearrange remaining electrons to satisfy octet rule (or duet rule for H)
For an Ionic Compound:
• Note that Potassium loses its valence electron to chlorine. The brackets indicate a negative charge around the chloride ion.
For Water:
Double BondsThere are times when double (or triple) bonds are needed in a molecule so that each atom
is surround by an octet of electrons
Multiple Lewis Structures - Resonance
Homework
Complete the two Lewis Structure
Handouts
Chemical Bondingand Molecular Structure
Chapter 12Sec 12.8 - 12.10
Goals:
1. To use Lewis Structures as a way to predict the geometry of Molecules
2. Determine if molecules are polar or nonpolar
VSEPR Model
• Valence Shell Electron Pair Repulsion Model
• Bonds (pairs of electrons) attempt to move as far away as possible from one another in a molecule
This explains the Geometry of H2O
Water is a “bent” molecule, because
of the lone pairs around the central
Oxygen atom
Various Geometry of Molecules
See Examples on Next Slides
(Hand-Out)
Polar or Non-polar Molecule?
A molecule may have polar covalent
bonds and not be polar overall
?????????
Geometry must also be considered
Ammonia (NH3) is polar
1. The bonds between hydrogen and nitrogen are polar covalent (∆EN = .87)
2. Pyramidal geometry of molecule points charges toward N
Carbon Dioxide is Non-polar
Even though the bonds between carbon and oxygen are polar covalent (∆EN = 1.0), the pull of electrons is in equal and opposite directions because CO2 is linear
Water is Wacky!
Water has some strange properties due to its structure