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Chapter
6B:
Chemical
Bonding
General
Chemistry
Mr. Mata
Cartoon courtesy of NearingZero.net
Standard 2a
• Atoms exchange electrons
to form an ionic bond.
Essential Question
• How do electrons behave
during ionic bonding?
6-3 Ionic Bonding and
Compounds
• Ionic Compound- composed of + and ions combined so charges are equal.
(Metal + nonmetal)
• Formula Unit- simplest group of
atoms form an ionic compound.
Cation Formation
• Main group metals lose all their
valence e-’s to form cations (+):
• This loss of electrons is called
oxidation.
.
• Na
Na1+ + 1esodium
• Mg:
Mg2+ + 2 emagnesium
.
• : Al
Al 3+ + 3 ealuminum
Anion Formation
• Non-metals gain e-’s to form anions (-).
• This process is called reduction.
Cl
O
N
123-
chloride (gain 1 e-)
oxide (gain 2 e-’s)
nitride (gain 3 e-’s)
Ionic Bond
•
•
•
•
- charges are attracted to + charges.
- anions are attracted to + cations.
The result is an ionic bond.
3-D crystal lattice of anions & cations
formed.
Structure of NaCl
Properties of Ionic
Compounds
•
•
•
•
•
Crystals form.
High melting point & boiling point.
Brittle (breaks easily).
Melt when heated (very high temps!)
Aqueous solutions conduct electricity.
(solutions mixed in water)
Electronegativity (EN)
• Atoms to the right & top of Periodic
Table have greater EN values.
• F most EN of elements (EN = 4.0).
• Fr least EN of elements (EN = O.7).
• Cl =3.0
H = 2.1
S = 2.5
• O = 3.5
Na = 0.9
Br = 2.8
• C = 2.5
N = 3.0
I = 2.5
Polar & Nonpolar Bonds
– H-H is non-polar because H & H have
the same EN’s. (EN diff. = 0)
– Cl-Cl is non-polar because Cl & Cl have
the same EN’s. (EN diff. = 0)
– H-Cl is polar because H & Cl have
different EN’s. ( H = 2.1, Cl = 3.0 )
Predicting Bond Type
• There is a continuum between non-polar
covalent bonds to ionic bonds.
• Non-polar bond; little difference in EN
between atoms. (EN diff. = 0 – 0.3)
• Ionic bonds; greatest EN diff between
atoms. (ΔEN > 1.7)
• Polar covalent bonds; in between EN
diff between atoms.
(EN diff. = 0.3 – 1.7)
Ionic vs. Covalent Bonds
Ionic Bonds
•
•
•
•
•
•
•
Exchange e-’s
Metal + non-metal
3-D units (crystals)
high mp/bp
Brittle, melt
Ex: NaCl
conduct electricity
Covalent Bonds
•Sharing e-’s
•non-metal + non-metal
•Molecular (low mp/bp)
• ex: CO2, Cl2
•Macromolecular (high
mp/bp)
•Ex: C(diamond), SiO2
•Non conductors
Ionic Bonding in NaCl
Ionic Bonding in NaCl
6-4 Metallic Bonding
• Metals- conduct heat, have low
ionization energy
• Low EN; give up electrons easily.
• Metals have luster (shine), are
malleable (can be hammered into
sheets) and are ductile (drawn into
wires).
Metallic Bonding
• Metallic Bonding - type of bonding
found in metallic crystals.
• 3-D lattice of positive ions.
• remain fixed in a crystal lattice.
• loosely-held valence e-’s move freely
throughout the crystal.
• The fluid-like movements of valence e-’s
make metals good conductors of heat
and electricity.
Metallic Bonding
Metal Alloys
• Alloys -metallic substances composed
of two or more elements; at least one
of these elements is a metal.
• Alloys are important because the
properties of an alloy are often
superior to those of its component
elements.
Common Metal Alloys
– Stainless steel (composed of Fe, Cr, C, Ni)
– Sterling silver (composed of Ag & Cu)
– 14 karat gold (composed of Au & Cu)
Note: Pure gold too soft for jewelry!)
– Brass/bronze (composed of Cu & Zn)
6-5 Molecular Geometry
• E- pairs around the central atom stay
as far apart as possible.
• Consider non-bonding (lone pairs) as
well as bonding e-’s.
• E- pairs in single, double and triple
bonds are treated as single e- clouds.
VSEPR Theory
• Valence Shell Electron Pair Repulsion
Theory (VSEPR)
• Two e- clouds around a central atom form a
linear shape as in CO2 and BeF2
• Three e- clouds form a trigonal planar
shape as in BF3
VSEPR Theory
• The shape formed by the four e- pairs
is called a tetrahedron as in CH4.
• In water, H2O, two of the corners
are occupied by hydrogens.
• Gives water molecule its bent shape.
Structure of H2O
• Bonded e- pairs are often represented
as lines:
•
:
• So H2O would look like this: :O
H
•
H
• There are a total of 2 e- pairs which try
to get as far away from each other as
possible. Result = bent shape.
Bent Shape of H2O
Hydrogen Bonding
• Hydrogen bonding - strongest of the
intermolecular bonds (bonds between
molecules).
• Hydrogen bonding - hydrogen atoms
bonded to highly EN elements such as
F, O, and N.
• Hydrogen bonding - responsible for
the relatively high MP & BP of water.
Chapter 6B SUTW Prompt
• Describe the different properties of
ionic bonds and metallic bonds by
describing how the electrons interact
with each bonding type.
• Complete an 8-10 sentence paragraph
using the SUTW paragraph format.
Hilight using green, yellow, and pink.
• Due Date: Tomorrow (start of class).