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

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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