chemical bonds

31
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

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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