1. Crystal Systems

2. Crystal System Terms Unit Cell
smallest repeating unit of a crystal structure
Slip Planes - surface along which layers of atoms can slide past one another
plane of closely packed atoms
Use the dowel set up to demonstrate slip planes. If the atoms are close together, other atoms can easily slip past, if the atoms are further apart, it is more difficult to slip past.

5. Crystal System Terms
Void or Interstice-
empty space in a crystal

6. Crystal Packing – loosely packed
Is there another way these atoms could be arranged?
Show next slide

7. Crystal Packing – More Densely Packed
Most metals are close packed - that is, they fit as many atoms as possible into the available volume
Alternating the atoms has made more room – the 4 halves could be joined and added to the bottom still leaving space.

8. Each group makes all of them but every group is making them at the same time---so all make b together and then all make c together and they talk about it
And then stack the layers
Have the kids make them but have the kids figure out what name goes with which structure
Then talk about gappiness and slip planes for each one---kids would write it down
For FCC—diagnol slip planes are harder to see—show the tennis ball model from Tom who is a retired NASA scientist who does taxes for a hobby for elderly…

9. HEXAGONAL CLOSE PACKED
SIMPLE CUBIC
FACE CENTERED CUBIC
(FCC)
BODY CENTERED CUBIC
(BCC)
Each group makes all of them but every group is making them at the same time---so all make b together and then all make c together and they talk about it
And then stack the layers
Have the kids make them but have the kids figure out what name goes with which structure
Then talk about gappiness and slip planes for each one---kids would write it down
For FCC—diagnol slip planes are harder to see—show the tennis ball model from Tom who is a retired NASA scientist who does taxes for a hobby for elderly…
HEXAGONAL CLOSE PACKED
(HCP)

10. BCC
simple cubic
FCC
HCP

11. Slip Planes of FCC Morton Schaffer
Let’s take a look at a FCC cubic structure and count the slip planes in this slip system. Even though there is a convention to name the planes, that level of detail is not within the scope of this course. Therefore, I’m just going to show pictorially where the planes are.

12. Slip Planes Morton Schaffer1

13. Slip Planes Morton Schaffer2

14. Slip Planes Morton Schaffer3

15. Slip Planes Morton Schaffer4

16. Slip Planes Morton Schaffer5

17. Slip Planes Morton Schaffer6

18. Slip Planes Morton Schaffer7

19. Slip Planes Morton Schaffer
Up to 48 Slip Planes
12 Slip Planes
center atom
As noted earlier, the more slip planes there are, the more ductile the material trends to be. Look at the examples of metals that have the indicated structure. Compare the properties of these metals and get a “feel” for why thes metals tend to behave the way they do. Keep in mind that slip planes do not necessarily determine how strong the metal is, but rather how easy it is to bend, form, etc. without tearing or breaking.
Body-centered cubic (BCC)
Face-centered cubic (FCC)
Hexagonal close-packed (HCP)
3 Slip Planes

20. Why do Crystal Systems Matter?
Workability
changing the shape of a solid without breaking or cracking
Malleability
ability of being hammered into thin sheets
Ductility
ability of being drawn into wires

21. Workability Which crystal structure is more workable?
Many slip planes or few slip planes?
Tightly packed or loosely packed?
Malleability and ductility is a type of workability
How easy you can manipulate a solid
Many slip planes determines good workability
Common sense
Common sense more gappiness has more room to move around—but not true—do ice tray demo
Less gappiness is more workable
Based on what we did and showed which crystal is more workable? FCC most packed and most slip planes

22. Type of crystal structure
Models of Crystals Lab
*more tightly packed = more workable
*more slip planes = more workable
Type of crystal structure
Closely packed?
Many slip planes?
Workability
FCC
BCC
HCP
This slide68 – S
Chalk Demo 62 - S

23. Type of crystal structure
Models of Crystals Lab
*more tightly packed = more workable
*more slip planes = more workable
Type of crystal structure
Closely packed?
Many slip planes?
Workability
FCC
Yes
Highest
BCC No
Medium
HCP
Lowest
This slide68 – S
Chalk Demo 62 - S

24. Crystal Structures & Metals
BCC
FCC
HCP
Other

25. Crystal Structures & Metals
BCC
FCC
HCP
Other
Chromium
Aluminum
Cobalt
Manganese
Iron (<910°C)
Calcium
Magnesium
tin
Molybdenum
Copper
Titanium
Sodium
Gold
zinc
tungsten
Iron (>910°C)
Lead
Nickel
Platinum
silver

26. Sargent Welch Periodic Table
Crystal structures on the back.

27. Growing Crystals
Sulfur Lab

28. Sulfur MSDS

29. Sulfur MSDS

30. Sulfur MSDS

31. Sulfur MSDS

32. Review lab on Friday!
Monday, 9/19/16

33. Part A – Rhombic Sulfur Heated in mineral oil to dissolve
Forming crystals from a solution
Heated in mineral oil to dissolve
Crystals formed in solution
Sketch and describe

36. Part B: Monoclinic Sulfur
Forming crystals from a melted substance
1. Fill a test tube approximately 1/2 full with sulfur. Keep the sulfur powder off the sides of the test tube.
2. Make a cone out of filter paper and place it in a funnel. (Make a sketch.)

38. Part B: Monoclinic Sulfur
3. Heat the test tube of sulfur very slowly - passing it back and forth above the flame. Totally melt to a liquid. Use Bunsen burner and test tube clamp. Keep the sulfur yellow. 4. Pour liquid sulfur into filter paper cone. As soon as a crust forms, open the filter paper to original shape.

40. Part B: Monoclinic Sulfur
5. Make observations of crystals formed. Use stereoscope. 6. Clean up!!!!!
Part B: Monoclinic Sulfur

44. Part C: Amorphous Sulfur
Heat sulfur slowly. It will pass through stages:
melt to yellow liquid
red liquid
dark reddish-brown thick syrup
dark runny liquid
Pour hot sulfur into beaker of cold water. (quench)
Like pouring maple syrup

45. Chain of
sulfur atoms
Ring of 8
sulfur atoms

48. dark reddish-brown thick syrup
melt to yellow liquid
individual rings of 8
red liquid
short chains of 8 – 16 sulfur atoms
dark reddish-brown thick syrup
longer chains of sulfur atoms that entangle
dark runny liquid
longer chains of sulfur atoms that have enough energy to flow

49. Amorphous Sulfur

50. Crystalline balls
of sulfur

51. Crystalline vs. Amorphous?
Orderly arrangement
Repeating pattern
Predictable
Opaque (not see through)
Random arrangement
No repeating pattern
Not predictable
Clear

52. Allotropes
Different forms of the same element in the same physical state
Difference is in how the atoms are arranged
Also called polymorphism
Examples:
Carbon – diamond, graphite, buckyballs
Oxygen – O2 (atmospheric) and O3 (ozone)
Sulfur – rhombic, monoclinic, amorphous

53. Allotropes of Carbon buckyball
Great web page about crystals

54. Allotropes of Sulfur
rhombic
amorphous
monoclinic

55. Solid State Phase Change
Change in crystal structure while remaining a solid.
Example:
Amorphous sulfur changing to crystalline sulfur

56. What is happening when you heat the plastic to the crystal structure?
Milk Jug Demo