Chemical Bonding and Molecular Structure Chapter 12 Sec Chapter 12 Sec

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 Bonds There 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 Bonding and Molecular Structure Chapter 12 Sec

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 H 2 O 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 (NH 3 ) 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 CO 2 is linear

Water is Wacky! Water has some strange properties due to its structure