Chapter 6 CHEMICAL BONDING

WHAT IS ELECTRONEGATIVITY? WHY DOES IT MATTER?

Section 5.1

INTRODUCTION TO CHEMICAL BONDING

Electronegativity- The ability for an atom to attract an electron to itself

There are 3 types of bonds Ionic BondCovalent BondPolar Covalent Bond

SECTION 6.1

Ionic bond- Electrons are transferred forming ions. These ions are attracted to each other. The bond is a strong force between the two atoms.

Covalent bond- two or more atoms sharing pairs of electrons

TYPES OF BONDS

Polar Covalent- two or more atoms sharing a pair of electrons unevenly

TYPES OF BONDS (CONT)

The type of bond between two or more atoms depends on the diff erence in electronegativity of the atoms.

ELECTRONEGATIVITY AND BONDING

Type of Bond Difference in Electronegativity

Ionic 1.8 - 3.3

Polar- Covalent 0.4 - 1.7

Covalent 0.0 - 0.3

What is the main distinction between ionic and covalent bonding?

How is electronegativity used in determining the ionic or covalent character of the bonding between two elements?

What type of bond would be expected between the following atoms? Li and F Cu and S I and Bf

SECTION 6.1: LEARNING CHECK

Section 6.2

COVALENT BONDING AND MOLECULAR

COMPOUNDS

Molecule- a neutral group of atoms that are held together by covalent bonds

Chemical formula- the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts

Octet- 8 electronsSingle bond- 1 electron pair sharedDouble bond-

TERMS TO KNOW

EXAMINE THESE COVALENT MOLECULES. WHAT DO YOU

NOTICE?

Overall goal: Obtain an octetCreate a stable atomLowest amount to energy

FORMATION OF A COVALENT BOND

Bond length: distance between two bonded atoms

Bond energy: the energy required to break a chemical bond and form neutral isolated atoms.

CHARACTERISTICS OF THE COVALENT BOND

Atoms will gain, lose, or share electrons to get 8 electrons in their highest occupied energy level

Exceptions: Helium and Hydrogen- only need 2 valence electronsBoron- has 3 electrons and is stable with 6 electrons

Example: BF3

Expanded Octet- Some atoms can hold more than 8 when they are bonded to extremely electronegative atoms. Example: PF5 and SF6

THE OCTET RULE

An electron configuration notation in which only the valence electrons of an atom of a particular element are shown.

ELECTRON-DOT NOTATION

Visual representation of molecules Element symbol- nuclei and inner-shell electrons Dot-pairs- non-bonding valence electrons Dashes- bond between two elements

LEWIS STRUCTURES

1. Determine the type and number of atoms in the molecule2. Write the electron-dot notation for each type of atom in the

molecule3. Determine the total number of valence electrons available

to be combined4. Arrange the atoms

1. If carbon is present it is in the center2. If not, the least electronegative atom is in the center

5. Add unshared pairs of electrons to each nonmetal atom (except hydrogen) Each atom needs to be surrounded by 8 electrons.

6. Count the electrons in the structure to be sure that the number of valence electrons used equals the number available.

7. Place non-bonding valence electrons in pairs around atoms without an octet

HOW TO DRAW LEWIS STRUCTURES?

NH3

H2S

SiH4

PF3

EXAMPLES:

Indicates the kind, number, arrangement, and bonds but not the unshared electrons.

STRUCTURAL FORMULA

H-Cl

Double or triple bonds Triple bonds are the shortest and strongest

covalent bondsThe need for a multiple bond becomes

obvious if there are not enough valence electrons to complete octets by adding unshared pairs.

MULTIPLE COVALENT BONDS

Compare the molecules H2NNH2 and HNNH

REVIEW

Bonding in molecules or ions that cannot be correctly represented by a single Lewis structure.

RESONANCE STRUCTURES