Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 1 of 69

Chemical Bonds

• Chemical Bonds

• The attractive forces that hold atoms together in molecules.

• Ionic Bonds

• Involve the transfer of electrons

(it conducts electricity)

• Covalent Bonds

• Involve the sharing of electrons

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 2 of 69

IONIC BONDS

• Exchange of electrons

• Metal with non-metal

• high melting point

• High boiling point

• brittle

• melt, solution conducts electricity

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 3 of 69

Ionic Compounds in Solution

H2O

When ionic compounds are dissolved

in water, they dissociate to form

aqueous ions:

NaCl(s) Na+(aq) + Cl-(aq)

The resulting solution conducts

electricity and is called an

electrolyte.

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 4 of 69

The Structure of

Salt

Sodium Chloride

(NaCl)

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 5 of 69

Metals physical properties

Tell me please?

?

?

?

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 6 of 69

Metallic Bonding

Metallic Bonding is the type of

bonding found in metallic crystals.

A metallic solid can be pictured as a

three-dimensional array of positive

ions that remain fixed in a crystal

lattice while the loosely-held valence

electrons move freely throughout the

crystal.

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 7 of 69

A Model of Metallic Bonding

The fluid-like

movements of

the valence

electrons make

metals good

conductors of

heat and

electricity.

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 8 of 69

Compare and contrast ionic and

covalent bonds.

Ionic Bonds

• Exchange of electrons

• metal/non-metal

• high mp/bp

• brittle

• melt, solution conduct electricity.

Covalent

• Sharing electrons

• non-metal/non-metal

• Molecular (low mp/bp)

• Macromolecular (high

mp/bp)

• Non conductors

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 9 of 69

Covalent Bonds

Classify a covalent bond… as polar

or non polar.

Polar Bonds result from the unequal

sharing of electrons.

Unequal sharing results when there is

a difference electronegativity between

the atoms involved.

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 10 of 69

Polar and non-polar bonds

H-H is non-polar because H & H have

the same electronegativity.

Cl-Cl is non-polar because Cl & Cl

have the same electronegativity.

H-Cl is polar because H & Cl have

different Electronegativities.

( H = 2.1, Cl = 3.0 )

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 11 of 69

Ionic Character Increases as the

Difference in Electronegativity Increases

Electronegativity difference0.4 1.7

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 12 of 69

Diatomic Elements

p.72

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 13 of 69

Ionic Character Increases as the

Difference in Electronegativity Increases

Electronegativity difference0.4 1.7

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 14 of 69

Compare and contrast ionic and

covalent bonds. Ionic Bonds

• Exchange of electrons

• metal/non-metal

• high mp/bp

• brittle

• melt, solution conduct electricity

Covalent

• Sharing electrons

• non-metal/non-metal

• Molecular (low mp/bp)

• Macromolecular (high mp/bp)

• Non conductors

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 15 of 69

Electronegativity

Generally speaking, atoms to the

right and top of the periodic table

have greater electronegativities.

F is the most electronegative of the

elements with an electronegativity

of 4.

Cs is the least electronegative at 0.7.

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 16 of 69

Non-polar, Polar, Ionic

There is a continuum between non-polar covalent bonds to ionic bonds.

Non-polar bond have no difference in electronegativity between the atoms.

Ionic bonds have the greatest difference in electronegativity

between the atoms. (ΔEN>1.7)

Polar covalent bonds have an intermediate difference in

electronegativity between the atoms.

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 17 of 69

Chemical Bonds

• Chemical Bonds

• The attractive forces that hold atoms together in molecules.

• Ionic Bonds

• Involve the transfer of electrons

• Covalent Bonds

• Involve the sharing of electrons

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 18 of 69

Ionic Character Increases as the

Difference in Electronegativity Increases

Electronegativity difference0.4 1.7

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 19 of 69

Compare and contrast ionic and

covalent bonds. Ionic Bonds

• Exchange of electrons

• metal/non-metal

• high mp/bp

• brittle

• melt, solution conduct electricity

Covalent

• Sharing electrons

• non-metal/non-metal

• Molecular (low mp/bp)

• Macromolecular (high mp/bp)

• Non conductors

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 20 of 69

Metallic Bonding

Metallic Bonding is the type of

bonding found in metallic crystals.

A metallic solid can be pictured as a

three-dimensional array of positive

ions that remain fixed in a crystal

lattice while the loosely-held valence

electrons move freely throughout the

crystal.

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 21 of 69

A Model of Metallic Bonding

The fluid-like

movements of

the valence

electrons make

metals good

conductors of

heat and

electricity.

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 22 of 69

K =

0.8

Na =

0.9

Ca =

1.0

Be =

1.5

Si =

1.8

H =

2.1

S =

2.5

C =

2.5

Br =

2.8

Cl =

3.0

N =

3.0

O =

3.5

ELECTRONEGATIVITY

I= 2.5, Mg= 1.2, F= 4

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 23 of 69

Chemical Bonds

• Chemical Bonds

• The attractive forces that hold atoms together in molecules.

• Ionic Bonds

• Involve the transfer of electrons

• Covalent Bonds

• Involve the sharing of electrons

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 24 of 69

Lewis Structures

Drawing of the electrons of the outer energy level.

“Valence Electrons”

(Dots around the element)

6C:1s2 2s2 2p2

Valence electrons=4

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 25 of 69

Octet Rule:

When ionic bonds are formed, metals

lose valence electrons so that the

electron configuration becomes like a

noble gas, leaving it with eight outer

electrons.

Non-metals gain electrons to become

like the next higher noble gas, usually

having 8 valence electrons.

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 26 of 69

• Main group metals lose all their valence electrons to form cations:

• This loss of electrons is called oxidation.

Na. Na+ + e-

Mg: Mg2+ + 2 e-

:Al. Al 3+ + 3 e-

Ions

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 27 of 69

Non-metals gain electrons to have the noble gas configuration and form anions:

This process is called reduction.

:Cl. + e- :Cl:- chloride

:O: + 2e- :O:2- oxide

:N. + 3e- :N:3- nitride

Anion Formation.

..

.:

: ::

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 28 of 69

Preserve Electroneutrality

When ions combine, electroneutralitymust be preserved.

In the formation of magnesium chloride,

2 Cl- ions must balance a Mg2+ ion:

Mg2+ + 2 Cl- MgCl2

In the formation of magnesium nitride,

3 Mg2+ ions balance 2 N3- ions:

3 Mg2+ + 2N3- Mg3N2

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 29 of 69

Octet Rule

• Recognize the importance of the octet rule.

• Atoms tend to gain lose or share electrons so that there are eight electrons in the outer shell.(except those that become like He)

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 30 of 69

Electronegativity

Electronegativity is defined as the

ability of an atom to attract electron

density to itself when joined to

another atom in a chemical bond.

The most electronegative elements

have the greatest attraction for

electrons.

Prentice-Hall ©2002 Burns 4/e Chapter 8 Slide 31 of 69

Insert Figure

8.6 Incre

ase

Electronegativities of Elements

Increase