Growing Crystals Background and Sulfur Lab

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

Crystal Definitions Grains Grain Boundary 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 A grain is merely a crystal without smooth faces because its growth was impeded by contact with another grain or a boundary surface. http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Structure/solidification.htm

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

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). http://www.ami.ac.uk/courses/topics/0122_mos/index.html

Snow - Ice Snow - ice

Dendritic copper crystals

Ways to form Crystals Solutions 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

Types of Solutions unsaturated saturated supersaturated 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

Growing Crystals – Sulfur MSDS

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.

Growing Sulfur Crystals Lab Three methods of growing crystals. Students: Follow directions in lab worksheet on how to perform. TAKE Safety precautions!!!!! Leave this slide here until lab is finished – lab may take whole period.

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?

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

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

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

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?

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

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

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

Supplementary Slides

Crystalline balls of sulfur