section 12.1 characteristics of chemical bonds 1.to learn about ionic and covalent bonds and explain...

Section 12.1

Characteristics of Chemical Bonds

1. To learn about ionic and covalent bonds and explain how they are formed

2. To learn about the polar covalent bond

3. To understand the nature of bonds and their relationship to electronegativity

4. To understand bond polarity and how it is related to molecular polarity

Objectives

Section 12.1


A. Types of Chemical Bonds

• Bond – force that holds groups of atoms together and makes them function as a unit

• Bond energy – energy required to break a chemical bond

Section 12.1



• Ionic compound results when a metal reacts with a nonmetal

Ionic Bonding

(a) (b)

Section 12.1



• A covalent bond results when electrons are shared by nuclei

Covalent Bonding

Section 12.1



• A polar covalent bond results when electrons are shared unequally by nuclei

Covalent Bonding

– One atom attracts the electrons more than the other atom

Section 12.1


B. Electronegativity

• Electronegativity – the relative ability of an atom in a molecule to attract shared electrons to itself – Increases from left to right across a period – Decreases down a group of representative elements

Section 12.1



• The polarity of a bond depends on the difference between the electronegativity values of the atoms forming the bond

Section 12.1



Section 12.1


C. Bond Polarity and Dipole Moments

• A dipole moment results when a polar molecule has a center for positive charge separate from a center for negative charge

Gretchen Adams

Should the sentence say "...has a center of positive charge separate from a center of negative charge"? (It seems to flow better in the textbook that way.)

Section 12.1



• Water molecule dipole moment

Section 12.1



• The polarity of water affects its properties

– Causes water to remain liquid at higher temperature

– Permits ionic compounds to dissolve in it

Section 12.2

Characteristics of Ions and Ionic Compounds

1. To learn about stable electron configurations

2. To learn to predict the formulas of ionic compounds

3. To learn about the structures of ionic compounds

4. To understand factors governing ionic size

Objectives

Section 12.2


A. Stable Electron Configurations and Charges on Ions

Section 12.2



• Atoms in stable compounds usually have a noble gas electron configuration

– Metals lose electrons to reach noble gas configuration – Nonmetals gain electrons to reach noble gas

configuration

Section 12.2



• Chemical compounds are always electrically neutral

Predicting Formulas of Ionic compounds

Section 12.2


B. Ionic bonding and Structures of Ionic Compounds

• Ions are packed together to maximize the attractions between ions

Structures of Ionic Compounds

Gretchen Adams

The B in "bonding" should be capitalized (in purple font)

Section 12.2



• Cations are always smaller than the parent atom

Structures of Ionic Compounds

• Anions are always larger than the parent atom

Gretchen Adams

Gretchen Adams2/7/2007The B in "bonding" should be capitalized (in purple font)

Section 12.2



• Polyatomic ions work in the same way as simple ions– The covalent bonds hold the polyatomic ion together so it

behaves as a unit

Ionic Compounds Containing Polyatomic Ions

Gretchen Adams

Gretchen Adams2/7/2007The B in "bonding" should be capitalized (in purple font)

Section 12.3

Lewis Structures

1. To learn to write Lewis structures

2. To learn to write Lewis structures for molecules with multiple bonds

Objectives

Section 12.3

Lewis Structures

A. Writing Lewis Structures

• In writing Lewis structures we include only the valence electrons

• Most important requirement– Atoms achieve noble gas electron configuration (octet

rule, duet rule)

Section 12.3

Lewis Structures


• Bonding pairs are shared between 2 atoms

• Unshared pairs (lone pairs) are not shared and not involved in bonding

Section 12.3

Lewis Structures


Section 12.3

Lewis Structures

B. Lewis Structures of Molecules with Multiple Bonds

• Single bond – covalent bond in which 1 pair of electrons is shared by 2 atoms

• Double bond – covalent bond in which 2 pairs of electrons are shared by 2 atoms

• Triple bond – covalent bond in which 3 pairs of electrons are shared by 2 atoms

Section 12.3

Lewis Structures


– A molecule shows resonance when more than one Lewis structure can be drawn for the molecule

Section 12.3

Lewis Structures


– Boron – incomplete octet

Some Exceptions to the Octet Rule

– Molecules containing odd numbers of electrons – NO and NO2

Section 12.4

Structure of Molecules

1. To understand molecular structure and bond angles

2. To learn to predict molecular geometry from the number of electron pairs

3. To learn to apply the VSEPR model to molecules with double bonds

Objectives

Gretchen Adams

The first word of the section is "Structures" not "Structure" and should be fixed on all of the slides.

Section 12.4


A. Molecular Structure

• Three dimensional arrangement of the atoms in a molecule – Water - bent

Section 12.4



• Linear structure – atoms in a line

– Carbon dioxide

Section 12.4



• Trigonal planar – atoms in a triangle

– BF3

Section 12.4



• Tetrahedral structure

– methane

Section 12.4


B. The VSEPR Model

• Valence shell electron pair repulsion (VSEPR) model – Molecular structure is determined by minimizing

repulsions between electron pairs

Section 12.4


B. The VSEPR Model

– 180o - linear

Two Pairs of Electrons

• BeCl2

Section 12.4


B. The VSEPR Model

– 120o – trigonal planar

Three Pairs of Electrons

• BF3

Gretchen Adams

In this slide, you don't show BF3 with bond angles of 90 degrees (like the graphic on pg. 426), but in the tetrahedral structure, you show CH4 with 90 degree angles and then the correct way. Would it be valuable to include this on this slide as well?

Section 12.4


B. The VSEPR Model

– 120o – tetrahedral

Four Pairs of Electrons

• CH4

Gretchen Adams

The bond angle on the bottom should say 109.5 degrees, not 120 degrees.

Section 12.4


B. The VSEPR Model

Section 12.4


C. Molecules with Double Bonds

When using VSEPR model to predict molecular geometry of a molecule

• a double bond is counted the same as a single electron pair

Gretchen Adams

For some reason the arrangement of the text on this slide looks strange to me. What if we re-formatted it to resemble slide 6 with a bullet first and then a dash?

section 12.1 characteristics of chemical bonds 1.to learn about ionic and covalent bonds and explain...

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