CHAPTER 9

Covalent Bonding

What You Will Learn…The nature of the covalent bondHow to name covalently bonded groups of atomsShapes of moleculesCharacteristics of covalent moleculesHow to compare and contrast polar and nonpolar molecules

Why It Is Important

Most compounds are covalently bonded

Including those in living organisms

AssignmentWrite out Chapter 9 vocabulary words and their definitions

14 words on page 271PLUS the octet rule from Chapter 6

The Covalent Bond

Section 9.1

ObjectivesApply the octet rule to atoms that bond covalentlyDescribe the formation of single, double, and triple covalent bondsCompare and contrast sigma and pi bondsRelate the strengths of covalent bonds to bond length and bond dissociation energy

Key TermsCovalent bondMoleculeLewis structure

Sigma bondPi bondEndothermicExothermic

Review Do noble gases bond?

Why or why not?What is an ionic bond?Fill in the blank:

In an ionic bond, electrons are_________from one ion to another.

What if both atoms need

valence electrons?

Sharing ElectronsAnother way atoms acquire noble gas configurationsOccurs when BOTH atoms want to gain valence electrons

What is the Octet Rule from Chapter

6?

Covalent BondBond that results from sharing valence electrons

Shared electrons become part of BOTH atoms’ outer energy level

Most between NONMETALS

Covalent vs Ionic

MoleculeFormed when two or more atoms bond covalently

Covalent bonds are often called molecular bonds

Diatomic MoleculesTwo atoms of the same element form a bondAttractive forces = Repulsive forcesExamples:

H2

O2

N2

Halogens: F2, Cl2, Br2, I2

Diatomic Fluorine

Each Fluorine has 3 lone pairs and 1 shared pair of electrons

Single Covalent Bond

2 electrons (or 1 pair) are shared between two atoms

Single Covalent Bond

Lewis StructureElectron-dot diagrams for moleculesDots represent lone pairs of electronsA line represents shared electrons

Lewis Structures

H-H

H ö:

H

Lewis StructuresGroup 7A Elements

7 valence electrons, need 1 more, form one single bond

Lewis StructuresGroup 6A Elements

6 valence electrons, need 2 more, form 2 single bonds

Lewis StructuresGroup 5A Elements

5 valence electrons, need 3 more, form 3 single bonds

Lewis StructuresGroup 4A Elements

4 valence electrons, need 4 more, form 4 single bonds

Practice Problems

Practice ProblemSection 9.1 #1 on page 874

Sigma BondAnother name for single covalent bonds

Electron pair is shared in the area centered between atomsValence orbitals overlap end to ends and s; s and p; p and p

Multiple Covalent Bonds

Atoms form noble gas configuration by sharing more than one pair or electrons between 2 atomsC, N, O, S

Double Bond2 pairs (or 4 electrons) of electrons are shared

Triple Bond3 pairs (or 6 electrons) of electrons are shared

Pi BondFormed when parallel orbits overlap to share electronsShared par occupies the space above and below the line that represents where the 2 atoms join together

Multiple Bonds1 sigma bondAt least 1 pi bond

Double Bond1 sigma bond1 pi bond

Triple BondOne sigma bondTwo pi bonds

Pi and Sigma

Strength of Covalent Bond

Distance between nucleiBond length= distance at maximum attraction

Bond dissociation energy= energy required to break bonds

Exothermic Reaction

More energy is released forming new bonds than is required to break bonds in the initial reactants

Endothermic Reaction

Greater amount of energy is required to break the existing bonds in the reactants than is released when the new bonds form in the products

QUESTIONS?

Homework6-12 on page 247Bonding Problems