Upload
laurikitikis-velazquez
View
102
Download
0
Tags:
Embed Size (px)
Citation preview
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 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 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.