Ionic Compounds
Chemical Bonding
IV
Lewis Structures
• Ionic – show transfer of e-
Ionic Bonds
• Ionic –
– transfer of electrons
– Positive and negative ions are attracted to each
other
– Metals and non-metals
Ionic Formulas
Common Ion Charges
1+
0
2+
3+ NA 3- 2- 1-
Ionic Formulas
z potassium chloride

yK+ Cl-
z magnesium nitride
yMg2+
N3-

z copper(II) chloride
yCu2+ Cl-

Ionic Formulas
sodium bromide
sodium oxide
iron(III) chloride
Types of Bonds
Covalent Bonding - True Molecules
Diatomic
Molecule
RETURN
Lewis Structures
Lewis Structures
• The center atom is the least electronegative
• The number of valence electrons in the molecule is
the sum of all the valence electrons of each
individual atom.
• Always draw lone pairs
Polyatomic Ions
• A positive ion loses electrons
• NH4 has 8 valance electrons in its dot structure
• A negative ion gains electrons
• NO2 has 18 valence electrons.
Resonance Structures
Vocabulary
CHEMICAL FORMULA
IONIC
COVALENT
Formula
Unit
Molecular
Formula
NaCl
CO2
Vocabulary
COMPOUND
2 elements
Binary
Compound
NaCl
more than 2
elements
Ternary
Compound
NaNO3
Vocabulary
ION
1 atom
2 or more atoms
Monatomic
Ion
Polyatomic
Ion
+
Na
NO3
-
Crystal Lattice
Properties of ionic bonds
• Brittle
– A force dislocates the crystal plane
• Dissolve in Water dissolving NaCl
– Water is a polar molecule which attracts
both + and – ions
• Conduct electricity if molten or
dissolved
– When the ions are not neutralized by
bonds, the electric current passes from ion
to ion.
• High Melting points
– Very strong bonds
Properties of Bonds
• Lattice Energy
– Energy released when one mole of an
ionic crystalline compound is formed
from gaseous or aqueous ions
Energy of Bond Formation
• Potential Energy Diagram
attraction vs. repulsion
no interaction
increased
attraction
Energy of Bond Formation
• Potential Energy Diagram
attraction vs. repulsion
increased
repulsion
balanced attraction
& repulsion
Energy of Bond Formation
• Bond Energy
– Energy required to break a bond
Bond
Energy
Bond
Length
Bond Strength vs. Length
• Which is Strongest?
Which is weakest?
Why? LiCl, NaCl, or KCl?
• Which is stronger? LiF
or LiCl? Why?
• Which is stronger, CaO
or LiF? Why?
• Which is stronger, CaO
or MgO? Why?
Bond Energy
• Which is stronger? N-N or N=N Why?
– N=N
Multiple bonds are stronger.
• Which is stronger? H-F , H-Cl, H-Br
Why?
– H-F
Shorter bond length – higher bond energy.
• How much energy is needed to break apart each
of the following bonds?
– HCl
– H2O
OH
NH3
CH4
Bond Polarity
• Most bonds are a
blend of ionic and
covalent
characteristics.
• Difference in
electronegativity
determines bond
type.
Bond Polarity
• Electronegativity
– Attraction an atom has for a shared pair of
electrons.
– higher e-neg atom  – lower e-neg atom +
Bond Polarity
• Nonpolar Covalent Bond
– e- are shared equally
– symmetrical e- density
– usually identical atoms
Bond Polarity
• Polar Covalent Bond
– e- are shared unequally
– asymmetrical e- density
– results in partial charges (dipole)
+


Bond Polarity
Nonpolar
Polar
Ionic
View Bonding Animations.
Bond Polarity
Examples:
• Cl2
• HCl
• NaCl
Dipole Moment
• Direction of the polar bond in a molecule.
• Arrow points toward the more e-neg atom.
+

H
Cl

Intermolecular vs. Intramolecular
• Molecular Bonding involves forces BETWEEN
molecules
H –FON dipoles
Dipole-dipole forces
Polar molecules are attracted to
positively and negatively charged
particles.
Ion - dipole forces: the reason for salts
dissolving in water
Determining Molecular Polarity
• Polar Molecules
– Dipole moments are asymmetrical and don’t
cancel .
O
H2O
H
net
dipole
H
moment
Determining Molecular Polarity
• Nonpolar Molecules
– Dipole moments are symmetrical and cancel
out.
F
Bond Polarity
BF3
F
B
F
London Forces
London Forces
Molecular Bonds
Bonds Between molecules
• Low melting points – weak bonds
• Non-polar molecules have weaker bonds than
polar
• Polar dissolves polar
• Non-polar dissolves non-polar
• Polar bonds have brittle structures.
solubility of polar molecules
Covalent Network
Covalent Networks
• Very hard, Not brittle – not made up of ions
• Crystal structure – creates a systematic
pattern of atoms
• High Melting point – strong covalent bonds
Types of Bonds
Metallic Bonding - “Electron Sea”
RETURN
Properties of Metallic Bonding
• Shiny – electrons are constantly filling unfilled
lower energy levels.
• Conducts electricity – electrons are free to
flow
• Malleable, ductile - electrons are free to flow
-no rigid planes of balanced charges.
• High Melting points – strong bonds