2. Goals for the next 2 days:
Draw simple representations of different types of solids that illustrate important aspects of their structure
Analyze models of different solid types in order to explain the properties of these substances.

3. Chemistry of Solids
Types of Solids

4. Intermolecular forces hold molecules together in a solid state

5. Chemistry of Solids
Types of Solids

6. Covalent Network Solids:
Composed of:
Non-metal atoms attracted to one another via covalent bonds

7. Non-metal Non-metal Non-metal Non-metal Non-metal Non-metal Non-metal

8. Covalent Network Solids:
Composed of:
Non-metal atoms attracted to one another via covalent bonds
There are NO DISTINCT MOLECULES!!!

9. Covalent Network Solids:
Diamond:
Every C atom is covalently bonded to 4 other C atoms

10. Covalent Network Solids:
Graphite:
Still C atoms, just arranged differently

11. Covalent Network Solids:
Graphite:
Still C atoms, just arranged differently
The layers slide off easily from one another, making it great for writing with!

12. Covalent Network Solids:
Composed of:
Non-metal atoms attracted to one another via covalent bonds
There are NO DISTINCT MOLECULES!!!
If a formula is given, what does it probably represent? (SiC, silicon carbide for example)

13. Covalent Network Solids:
Silicon carbide:
SiC
Ratio:
1 Si atom for every 1 C atom

14. Covalent Network Solids:
Composed of:
Non-metal atoms attracted to one another via covalent bonds
There are NO DISTINCT MOLECULES!!!
Formula’s for covalent network solids only represent the ratio between the atoms in the solid

15. Covalent Network Solids:
How to ID them?
There are very few common examples of covalent network solids …
Look for substances with Si and/or C!!!

16. Covalent Network Solids: Melting Point:
Remember  this is based on the strength of whatever force holds the solid together!
(Intramolecular forces are always strongest)
Extremely high melting points
Carbon(diamond) has the highest melting point of any pure substance: 6,300oF

17. Covalent Network Solids:
Electrical Conductivity:
Remember  Free flowing charged particles are needed
Covalent network solids are NOT predicted to conduct electricity
Some do however …

18. Covalent Network Solids: Thermal Conductivity:
Good thermal conduction = easy to increase the movement of the particles
Very poor thermal conductors
Since every atom is covalently bonded to many others, it is hard to increase movement between them

19. Covalent Network Solids:
Thermal Conductivity:
Covalent network solids are thermal insulators!

20. Covalent Network Solids:
Hardness Scale:
Hardness is the resistance to various kinds of permanent shape change
Cov. network solids comprise the hardest substances known to man

21. Ionic Solids:
Composed of:
Ions attracted to one another via ionic bonds

22. Anion- Anion - Anion - Anion -
Cation +
Anion -
Cation +
Anion -
Cation +
Anion -
Cation +
Anion-
Cation +
Anion -
Cation +
Anion -
Cation +
Anion -
Cation +
Anion -
Cation +
Anion -
Anion -
Cation +
Cation +
Anion -
Cation +
Anion -
Cation +
Anion -
Cation +

23. Ionic Solids:
Composed of:
Ions attracted to one another via ionic bonds
How to ID them?
Look for compounds made of metals and non-metals …
Ex: NaCl, MgO, Al2S3

24. Melting points of ionic solids
You have two competing factors here. As the charge increases on the ions the bonds get stronger. However, as the distance between atoms increases the bonds get weaker. Let's look at some data first:
Melting Points
MgO °C BaO °C NaCl °C KCl 790 °C
As you can see the +2 ions (Mg+2 and Ba+2) have much higher melting points than the +1 ions (Na+1 and K+1). Now if you compare the two +2 ions, magnesium has a much smaller radius than barium which appears further down on the periodic table. You would predict MgO to have a higher melting point than BaO for that reason (much higher because they are far apart on the table). Similarly, potassium has a larger radius than sodium which you can infer from its position on the periodic table. So NaCl has a higher melting point than KCl (but not by much as they are quite close on the table)

25. Generally higher compared to other solids
Ionic Solids:
Melting points:
Generally higher compared to other solids
mp = 801oC
mp = 993oC

26. Generally higher compared to other solids
Ionic Solids:
Melting points:
Generally higher compared to other solids
lower
higher

27. Electrical conduction: (solid, molten, dissolved)
Ionic Solids:
Electrical conduction: (solid, molten, dissolved)
Solid
Molten
Dissolved
No conduct!
Conducts!
Conducts!

28. Ionic Solids:
Hardness: + - + - + - + - + - + - + - + - + - + - + - + - +

29. Ionic Solids:
Hardness: - + - +
When impacted, rows of ions re-align. + + - + - - - + - + + + - + - - - + - + +

30. Ionic Solids:
Hardness: - + - +
When impacted, rows of ions re-align. + - + - - + - + + - + -
If like charges face each other, the entire row is repelled away - + - +

31. Ionic Solids:
Hardness: - + - +
Ionic compounds tend to be very brittle + - + - - + - + + - + - - + - +

32. Practice problems 1d-f, 2, 3 and 5

33. Practice problems 1d-f, 2, 3 and 5