Chapter 22
Compounds Between Metals and
Non-Metals – the Ionic Bond
Called Salts
Band Gap
semiconductors

Near the boundary
between metals and
non-metals

Conduction and
valence bands do not
overlap
conduction
band
band gap
valence
band
E= h times frequency;
c= wavelength times frequency
Red longer wavelength
means lower frequency,
lower energy.
Red photons are emitted
from a warm LED; orange photons are
emitted when the LED is very cold.
What happened?
A. The band gap shrinks when
the semiconductor gets cold.
B. No “red” electrons get kicked
upstairs to fall back down.
C. The band gap increases when
the semiconductor gets cold.
Did you read
chapter 22 before coming to
class? Or do you have a
Halloween costume?
Yes
b) No
a)
Which element
will react with water in a way
most similar to Na?
O
b) Cl
c) Li
d) Hg
a)
Which of the
following has the highest
ionization energy
a)
b)
c)
d)
Na (Z=11)
Al (Z=13)
Cl (Z=17)
Ne (Z=10)
Ionization Energies


Nobel gasses have largest ionization energies.
Alkali metals have the least.
Compare and Contrast:
Ionic Compounds vs Metals





Network Solids
High melting T’s
Brittle solids
Don’t conduct heat and
electricity in solid
Often colorless and
usually transparent in big
chunks (White when powdered)
WHY?





Network Solids
High melting T’s
Malleable
Good conductors of heat
and electricity in solid
Opaque
Why???
Many closely spaced energy levels
with mobile electrons
Compare and Contrast:
Metals vs Non-Metals

Metals




Large atoms
Few valence electrons
Low ionization
energies
Non-metals



Small atoms
Many valence electrons
High ionization
energies
Why do metals and non-metals react?
Principles of reactivity:
materials react to lower energy and
increase entropy of universe
How can energy be lowered?
Metals lose valence electrons
Non-metals gain valence electrons
Energy levels
not drawn to scale.
Cl levels much
lower in energy!
Transfer of electron from Na
to Cl is downhill energetically
What about entropy change?
 2Na
+ Cl2 = 2NaCl + lots of heat and light
Na – speck Cl2 yellow gas
sand at bottom
Quicktime Video of reaction
Heat and light – cause an increase
in entropy of the surroundings
What are the products? IONS
neutral
atom
Positive
ion
Neutral
Cl atom
Negative
Cl ion
Negatively charged
Positively charged
Chloride ions
Sodium ions
35 protons, 36 electrons
(11 protons, 10 electrons)
Electrons belong to individual ions;
they are not shared among ions.
Examples of Ionic Compounds
NaCl
Al2O3
Na2O
Ions: same charges
Ions: different
Ions: similar sizes,
and similar sizes
charges and sizes
but different charges
Describe the structure of each compound: Do ions of one type cluster
together?
What type of ion immediately surrounds a given ion?
How do the answers to these two questions relate to the electric force law?
What prediction could you make about the
arrangement of ions in any ionic compound?
Which structure is the form
adopted by Al2O3 in nature?
A.
B.
What factor most likely
prohibits this structure?
Strong repulsive forces
between negative O ions
and between positive Al
ions
B. Not electrically neutral
C. Low entropy organization
A.
Compare & Contrast
Energy Levels
IONIC COMPOUND
ENERGY LEVELS
few levels -- spaced very far apart
Metal Energy Levels
many closely spaced levels
spread out over many nuclei
Energy Levels Explain

Ionic Salts
Transparent in
Visible Region of
Spectrum –
But absorb in UV

Metals
Opaque – absorb in
IR, Visible and UV
(exception: salts containing
certain transition metal ions
absorb in visible region.)
l20newcrystal.swf
l20photon.swf
Compare and Contrast
Electron Locations & Mobilities
IONIC COMPOUNDS
+
+
+
+
+
+
+
+
+
Electrons – localized on
individual nucleus
(spherically shaped
electron clouds in most ions)
METALS AND ALLOYS
Sea of Electrons – mobile;
electron density is spread out
over many nuclei, delocalized.
How does the model explain properties
of salts (ionic compounds) ?

High melting and
boiling temperatures?



Strong attractions
between + and – ions
Attractive forces act over
fairly large atomic
distances
Brittleness?

Strong repulsions when
ions with like charge
come together; material
shatters to relieve the
stress.
ELECTRICAL CONDUCTIVITY:
Flow of electricity requires charge carriers
that are free to move.

In solid, ions are fixed rigidly in
place. No Current can flow!
Melting frees up ions
so that they can move,
completing the electrical
circuit.
Dissolving salt in water also
frees up ions. Current flows!
Even More Properties
 Why

are some ionic materials colored?
Because they contain “transition” metals with
more energy levels for electrons
• Example: Ruby
Absorbs blue photons
Absorbs green photons
Doesn’t absorb
red photons:
reflects red
What Ions Usually Form?
Using the Periodic Table to make predictions.
Valence Electrons of Main Group Elements
Unreactive
noble gases
don’t form
ions.
Metals LOSE their
valence electrons.
Non-metals GAIN enough valence
electrons to become “noble”.
The octet rule
 Atoms
will most likely form an ion that has
the ns2np6 configuration of the closest
noble gas atom.


Metals take on this configuration by losing
electrons
Non-metals take on this configuration by
gaining electrons
Families

Chlorine and Fluorine will form the same types of
compounds since their valence electrons are the
same number and same orbital type.
3d
3p
3s
3d
3p
3s
2p
2s
2p
2s
9F
17Cl
1s
1s
When Mg loses its two
electrons, it has the same valence
electron configuration as
A. He, 1s2
2
6
B. Ne, 2s 2p
2
6
C.Ar, 3s 3p
D.Kr, 4s24p6
When Br gains one electron, it has
the same valence electron configuration as
1.
2.
3.
4.
He, 1s2
Ne, 2s22p6
Ar, 3s23p6
Kr, 4s24p6
Beryllium (Be) will
most likely form an ion
with what charge?
a)
b)
c)
d)
-1
-2
+1
+2
What would the
chemical formula for magnesium
fluoride (a salt of Mg and F) be?
a)
b)
c)
d)
MgF
Mg2F
MgF2
MgF3
Ionic compounds are
neutral (no net charge). What are the ionic
charges in the following compounds?
 NaCl
 Na+1
and Cl-1
 KBr
 K+1
 MgF2
 Mg+2
 Al2O3
 Al+3
and Br-1
and F-1
and O-2
Naming convention for salts
 The
metal comes first with its name
unchanged
 The nonmetal comes second, with the
suffix “ide” appended