1. Compounds Between Metals and Non-Metals – the Ionic Bond Called Salts
Chapter 22
Compounds Between Metals and Non-Metals – the Ionic Bond
Called Salts

2. Band Gap semiconductors
Near the boundary between metals and non-metals
Conduction and valence bands do not overlap
valence
band
conduction
band gap

3. E= h times frequency; c= wavelength times frequency
Red longer wavelength means lower frequency, lower energy.

4. Red photons are emitted from a warm LED; orange photons are emitted when the LED is very cold. What happened?
The band gap shrinks when the semiconductor gets cold.
No “red” electrons get kicked upstairs to fall back down.
The band gap increases when the semiconductor gets cold.

5. Did you read chapter 22 before coming to class
Did you read chapter 22 before coming to class? Or do you have a Halloween costume?
Yes No

6. Which element will react with water in a way most similar to Na?Cl Li Hg

7. Which of the following has the highest ionization energy
Na (Z=11)
Al (Z=13)
Cl (Z=17)
Ne (Z=10)

8. Ionization Energies Nobel gasses have largest ionization energies.
Alkali metals have the least.

9. 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)
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
WHY?

10. Compare and Contrast: Metals vs Non-Metals
Large atoms
Few valence electrons
Low ionization energies
Non-metals
Small atoms
Many valence electrons
High ionization energies
For a given row
Why do metals and non-metals react?
Principles of reactivity:
materials react to lower energy and
increase entropy of universe

11. How can energy be lowered?
Metals lose valence electrons
Non-metals gain valence electrons
Transfer of electron from Na
to Cl is downhill energetically
Energy levels
not drawn to scale.
Cl levels much
lower in energy!

12. 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

13. What are the products? IONS
neutral
atom
Neutral
Cl atom
Negative
Cl ion
Positive
ion
Negatively charged
Chloride ions
35 protons, 36 electrons
Positively charged
Sodium ions
(11 protons, 10 electrons)
Electrons belong to individual ions; they are not shared among ions.

14. Examples of Ionic Compounds
Ions: same charges
and similar sizes
NaCl
Ions: similar sizes,
but different charges
Na2O
Ions: different
charges and sizes
Al2O3
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?

15. Which structure is the form adopted by Al2O3 in nature?1 2 10 of 5 B.
Answer Now

16. What factor most likely prohibits this structure?
Strong repulsive forces between negative O ions and between positive Al ions
Not electrically neutral
Low entropy organization of 5 10
Answer Now

17. Compare & Contrast Energy Levels
IONIC COMPOUND ENERGY LEVELS
Metal Energy Levels
many closely spaced levels
spread out over many nuclei
few levels -- spaced very far apart

18. Energy Levels Explain Ionic Salts Transparent in
Visible Region of Spectrum –
But absorb in UV
(exception: salts containing certain transition metal ions
absorb in visible region.)
Metals
Opaque – absorb in
IR, Visible and UV
l20newcrystal.swf
l20photon.swf

19. Compare and Contrast Electron Locations & Mobilities
IONIC COMPOUNDS
METALS AND ALLOYS +
Electrons – localized on
individual nucleus
(spherically shaped
electron clouds in most ions)
Sea of Electrons – mobile;
electron density is spread out
over many nuclei, delocalized.

20. 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.

21. Dissolving salt in water also frees up ions. Current flows!
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!

22. 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

23. What Ions Usually Form. Using the Periodic Table to make predictions
What Ions Usually Form? Using the Periodic Table to make predictions. Valence Electrons of Main Group Elements
Metals LOSE their
valence electrons.
Unreactive
noble gases
don’t form
ions.
Non-metals GAIN enough valence electrons to become “noble”.

24. 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

25. Families
Chlorine and Fluorine will form the same types of compounds since their valence electrons are the same number and same orbital type. 1s 2s 2p 3d 3p 3s 1s 2s 2p 3d 3p 3s 9F
17Cl

26. When Mg loses its two electrons, it has the same valence electron configuration as
Ne, 2s22p6
Ar, 3s23p6
Kr, 4s24p6

27. When Br gains one electron, it has the same valence electron configuration as
Ne, 2s22p6
Ar, 3s23p6
Kr, 4s24p6

28. Beryllium (Be) will most likely form an ion with what charge?-1 -2 +1 +2

29. What would the chemical formula for magnesium fluoride (a salt of Mg and F) be?
MgF
Mg2F
MgF2
MgF3

30. Ionic compounds are neutral (no net charge)
Ionic compounds are neutral (no net charge). What are the ionic charges in the following compounds?
NaCl
KBr
MgF2
Al2O3
Na+1 and Cl-1
K+1 and Br-1
Mg+2 and F-1
Al+3 and O-2

31. Naming convention for salts
The metal comes first with its name unchanged
The nonmetal comes second, with the suffix “ide” appended