Chapter 8 Part 1: Ionic Bonding
Read:
HW:
• IONIC
BLB 2.7–2.8; 8.1–8.2
BLB 2: 51, 53, 57, 59, 65, 67;
8:16, 22, 25
Sup 2:4, 5; 8:1
electrons traded to form separate ions
both have noble
gas __________
Know:
Ionic Bonding
• Lewis Symbols
• Nomenclature
• Lattice energy
Na
Bonus deadline for Skill Check Tests Approaching??
____________________________________________
When is Exam 1??____________________________
!Data sheet and periodic table in the packet will be
provided during the exam
Bring:
pencils,
student ID
and a calculator—NO text-programmable
calculators or wireless devices
+
Cl!
• COVALENT
electrons shared between a few nuclei
distinct molecules
______ e !
____ e!
• METALLIC
electrons shared among all nuclei
_________ e!
__________ e !
“sea of electrons”
Dr. Lori Stepan Van Der Sluys
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Chapter8 Part 1
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Chapter8 Part 1
For ionic and covalent bonding:
Keep track of electrons with
Lewis Dot Symbols
Knowing the Number of Valence Electrons,
You Should be Able to Draw These:
1. ______________ electrons are involved in
bonding; represent each electron with
one dot
.
·C·
·
C
4 valence electrons
2
S [Ne] 3s 3p
4
.
:S:
·
____ valence electrons
2. Octet rule: elements tend to gain, lose or
share electrons so as to gain an
_____________ configuration of 8 electrons.
(Duet for H and He instead of octet)
" Inert gases have 8 valence electrons
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Chapter8 Part 1
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Chapter8 Part 1
IONIC BONDING
Ionic Bonding
Involves Transfer of _____________ to
form charged _____________
Ionic bond is due to electrostatic attraction.
Coulomb's Law:
Q1 - charge on 1st atom
Q2 - charge on 2nd atom
d - distance between charges
Electrons are exchanged to from separate ions
with complete _____________.
Na+
Cl!
1s2 2s2 2p6
1s2 2s2 2p6 3s23p6
[Ne]
[Ar]
complete octets
IONIC COMPOUNDS
• distinct +/! ions
• # crystal lattice
• strong omnidirectional electrostatic bonds
Characteristics
1. low electrical conductivity as solids (high as
liquids)
2. very high melting, boiling points
3. hard but brittle
4. soluble only in polar solvents (water)
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Chapter8 Part 1
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Chapter8 Part 1
Ionic compound: a compound that
consists of positive and negative ions.
Naming Inorganic Compounds and Ions
See Section 2.8
Metal + nonmetal
Examples:
NaCl
K2SO4
Mg(NO3)2
NH4Cl
Ionic compounds have ________ melting
points and are brittle (many are ________).
Molecular compounds: compounds
consisting of individual molecules
All nonmetals or nonmetals plus metalloids.
Examples:
HCl
H 2O
CH3COOH
NH3
Molecular compounds usually have
_______ melting points (many are _______
or __________).
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Chapter8 Part 1
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Chapter8 Part 1
Figure 2.26
Be able to fill in information as in the table below:
Name
potassium ion
Formula
CO32!
ammonium ion
Figure 2.27
sodium bicarbonate
H2SO4
Combine Ca+2 and PO43!
Figure 2.28
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Cu(II) and sulfate ion
Chapter8 Part 1
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Chapter8 Part 1
Formation of ionic salts from the
elements is very exothermic.
Na+(g) + Cl! (g) $ NaCl(s)
%H = -788 kJ/mol
BUT
• Removing an electron from a metal is
__________________.
Na(g) $ Na+(g) +e
%H = +496 kJ/mol
• And adding an electron to a nonmetal is moderately ______________.
Cl(g) +e $ Cl (g)
%H = -349 kJ/mol
Overall the process seems like it would
be endothermic.
Why is formation of an ionic salt so
favorable?
The added stability is due to the
attraction of the ions for each other. The
attraction brings the ions close, releases
energy, and forms a ________________.
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Chapter8 Part 1
Strength of Ionic Bond
(Lattice Energy)
Lattice Energy measures the strength of
the ionic interaction.
Definition:
NaCl(s) $Na+(g) + Cl! (g)
%H = +786 kJ/mol = Lattice Energy
• LE cannot be determined experimentally
• Use Hess’ Law (and known atomic
properties) to get the value of the
lattice energy.
Born-Haber Cycle
• By Hess's Law, the enthalpy of formation is
equal to the sum of the energies of several
individual steps.
• Reasons for the stability of ionic compounds is
made clear.
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Chapter8 Part 1
Lattice Energy
NaCl
MgO
Salts and Ionic Lattices
E = 786kJ
E =3934kJ
Why the big difference???
E!
Q1 Q2
d
Different salts have different Q’s and d's
NaCl
MgO
ION SIZES:
Ion sizes are important in ionic bonds
Compare melting points:
NaF
993oC
NaCl
801oC
larger
o
NaBr
747 C
anion
o
NaI
661 C
MgO
2800oC
higher charge
Trends:
Melting point increases as charge
_________________.
Radii
+
Na
Cl !
0.97Å
1.81Å
2.78Å
+2
Mg
2
O!
0.66Å
1.40Å
2.06Å
d is ______ for MgO
Melting point increases as lattice energy
_________________.
Melting point increases as size
_________________.
SO: lattice energy for MgO is more than 4x greater
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Chapter8 Part 1
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Chapter8 Part 1
Which one of the following expresses
the correct relationship between the
melting points of the 3 ionic solids NaCl,
MgS, and BaS?
1
2
3
4
5
NaCl > MgS > BaS
NaCl > BaS > MgS
MgS > BaS > NaCl
MgS > NaCl > BaS
BaS > MgS > NaCl
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Chapter8 Part 1