Crystal Systems

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.

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

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

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.

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 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)

BCC simple cubic FCC HCP

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.

Slip Planes Morton Schaffer 1

Slip Planes Morton Schaffer 2

Slip Planes Morton Schaffer 3

Slip Planes Morton Schaffer 4

Slip Planes Morton Schaffer 5

Slip Planes Morton Schaffer 6

Slip Planes Morton Schaffer 7

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

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

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

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

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

Crystal Structures & Metals BCC FCC HCP Other

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

Sargent Welch Periodic Table Crystal structures on the back.

Growing Crystals Sulfur Lab

Sulfur MSDS

Sulfur MSDS

Sulfur MSDS

Sulfur MSDS

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

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

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.)

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.

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

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

Chain of sulfur atoms Ring of 8 sulfur atoms

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

Amorphous Sulfur

Crystalline balls of sulfur

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

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

Allotropes of Carbon buckyball http://boomeria.org/chemlectures/crystals/crystals.html Great web page about crystals

Allotropes of Sulfur rhombic amorphous monoclinic

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

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