Growing Crystals Background and Sulfur Lab

1. Growing CrystalsBackground and Sulfur Lab

2. Crystal -Review • Definition: group of atoms that form a particular repeating pattern • Today we will try to grow some crystals and observe the properties.

3. Crystal Definitions • Grains • individual crystals in a solid • start growing in different places and meet up • Grain Boundary • where grains meet up in a solid • smaller crystals have more grain boundaries • affect physical properties

4. Crystal Definitions • Dendrites • crystal branches • crystal growth pattern – directional • grow until they eventually become large enough to impinge upon (interfere with) each other • spaces between the dendrite arms crystallize to make a more regular crystal

5. Once nucleated, the dendrites spread sideways and the secondary arms generate further tertiary arms and so on. When solidification is complete, all the dendrites that have formed knit together to form grains (or crystals).

6. Snow - Ice

7. Dendritic copper crystals

8. Ways to form Crystals • Cooling a liquid from a melt (freezing) • Grow as a precipitate from a chemical reaction • From a solution as the solvent cools or evaporates Solutions • Solution: homogeneous mixture • involves dissolving, physical process • Solute: material that gets dissolved • Solvent: material that does the dissolving • Example: Sugar dissolving in water

9. Types of Solutions • unsaturated • can hold (dissolve) more solute • saturated • no more solute can dissolve at that particular temperature • supersaturated • more solute is dissolved than it can normally hold at a particular temp • heat it, then cool it

10. Growing Crystals –Sulfur MSDS

11. Sulfur MSDS Safety Notice: The ignition temperature of sulfur here is very low - FIRE HAZARD! Have wet towels available to smother the flame. Take care not to burn hands! Sulfur Dioxide is toxic. Dispose of in trash can.

12. Growing Sulfur Crystals Lab • Three methods of growing crystals. • Students: Follow directions in lab worksheet on how to perform. • TAKE Safety precautions!!!!!

13. Journal • List your lab partners. • Problems and successes in lab technique – Part B. • Do you observe differences in the different crystals formed by the different methods?

14. Background on Sulfur • Sulfur Electron Configuration: • 1s2 2s2p6 3s2p4 • Can acquire two electrons or donate e- • Sulfur Molecule – S8 • Sulfur is nonpolar • Does not dissolve in water! • Only in nonpolar solvents

15. Structures of Sulfur Chain of sulfur atoms Ring of 8 sulfur atoms

16. Sulfur Structures Observed • 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

17. Solid State Phase Change • Change in crystal structure while remaining a solid • Example: Allotropes • Amorphous sulfur changing to crystalline sulfur • What other elements have allotropes?

18. 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) • Iron – BCC to FCC transition at high temperatures

19. Allotropes of Sulfur • Sulfur forms more than 30 types of allotropes! monoclinic rhombic amorphous

20. Allotropes of Carbon buckyball

21. Supplementary Slides

22. Crystalline balls of sulfur