CHAPTER 9 Covalent Bonding

What You Will Learn… The nature of the covalent bond How to name covalently bonded groups of atoms Shapes of molecules Characteristics of covalent molecules How to compare and contrast polar and nonpolar molecules

Why It Is Important Most compounds are covalently bonded Including those in living organisms

Assignment Write out Chapter 9 vocabulary words and their definitions 14 words on page 271 PLUS the octet rule from Chapter 6

The Covalent Bond Section 9.1

Objectives Apply the octet rule to atoms that bond covalently Describe the formation of single, double, and triple covalent bonds Compare and contrast sigma and pi bonds Relate the strengths of covalent bonds to bond length and bond dissociation energy

Key Terms Covalent bond Molecule Lewis structure Sigma bond Pi bond Endothermic Exothermic

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 Electrons Another way atoms acquire noble gas configurations Occurs when BOTH atoms want to gain valence electrons

What is the Octet Rule from Chapter 6?

Covalent Bond Bond that results from sharing valence electrons Shared electrons become part of BOTH atoms’ outer energy level Most between NONMETALS

Covalent vs Ionic

Molecule Formed when two or more atoms bond covalently Covalent bonds are often called molecular bonds

Diatomic Molecules Two atoms of the same element form a bond Attractive forces = Repulsive forces Examples: H 2 O 2 N 2 Halogens: F 2, Cl 2, Br 2, I 2

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 Structure Electron-dot diagrams for molecules Dots represent lone pairs of electrons A line represents shared electrons

Lewis Structures H-H H ö: H

Lewis Structures Group 7A Elements 7 valence electrons, need 1 more, form one single bond

Lewis Structures Group 6A Elements 6 valence electrons, need 2 more, form 2 single bonds

Lewis Structures Group 5A Elements 5 valence electrons, need 3 more, form 3 single bonds

Lewis Structures Group 4A Elements 4 valence electrons, need 4 more, form 4 single bonds

Practice Problems

Practice Problem Section 9.1 #1 on page 874

Sigma Bond Another name for single covalent bonds  Electron pair is shared in the area centered between atoms Valence orbitals overlap end to end s 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 atoms C, N, O, S

Double Bond 2 pairs (or 4 electrons) of electrons are shared

Triple Bond 3 pairs (or 6 electrons) of electrons are shared

Pi Bond Formed when parallel orbits overlap to share electrons Shared par occupies the space above and below the line that represents where the 2 atoms join together

Multiple Bonds 1 sigma bond At least 1 pi bond

Double Bond 1 sigma bond 1 pi bond

Triple Bond One sigma bond Two pi bonds

Pi and Sigma

Strength of Covalent Bond Distance between nuclei Bond 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?

Homework 6-12 on page 247 Bonding Problems