Chemistry is Crystal Clear

Root, Linda Everett Elementary

Objectives: Students will be able to: -Identify crystals -Understand how crystals are formed -Understand that crystals have six basic shapes -Compare crystals of various substances -Observe that crystals can be recovered by various means Apparatus Needed: Something porous: piece of brick lump of charcoal piece of cement Table salt Saucepan Water Hot plate Laundry bluing Several tall instant Household ammonia coffee jars Sugar Pencil Alum (available at drugstores) Paper clip Salol (Phenyl salicylate) Several petri dishes Food coloring Overhead projector Cotton thread Hand lenses Several shallow Poster paper glass bowls Large and small Craft wire styrofoam balls Recommended Strategy: 1. Before the lesson is presented, grow one or more crystal gardens, and recover a variety of crystals from solutions. You may use salt, sugar, alum, or other compounds of your choice. (See Borgford and Summerlin, Chemical Activities, American Chemical Society)

2. To introduce the lesson, display the crystals you have grown, along
with saucers or petri dishes of salt, sugar, and alum granules. Do
not identify the items by name, merely by number. Allow the children
about ten minutes to observe the items on display in detail with a hand
lens, comparing and contrasting them as they study them. A discussion
of their observations should follow.

3. Review the three states of matter-solids, liquids, and gases- and
their properties. Present the concept of amorphous and crystalline
solids. A transparency showing the structure of each should be
projected on the screen during the discussion.

4. Narrow the discussion to salt crystals. Show a transparency and a
model of a unit cell of salt and a salt lattice. (The model can be
made with the craft wire and the styrofoam balls.) Discuss how the
lattices form. Refer to the items on display, reminding them that what
they are seeing are lattices, not individual units.

5. Discuss the six basic shapes of crystals, while displaying an
example of each shape on a transparency. Relate these examples to the
crystals the children have already observed from the examples.

6. Review the definition of a saturated solution, and discuss how each
of the sample items was made. Discuss the fact that crystals are
formed through cooling and evaporation. Explore the concept that
crystals can be recovered from vapors, molten materials, and
solutions. Give examples of each in nature. (Snowflakes, diamonds,
and salt crystals would be an example of each.) The slower the
evaporation or cooling process, the larger the crystal.

7. To visually demonstrate crystal formation, heat a small amount of
phenyl salicylate in a petri dish on a low setting on the hot plate
until the crystals melt. Put the petri dish on the overhead. Seed it
with a pinch of phenyl salicylate and watch as the liquid cools, and
the crystals begin to form. The process can be repeated many times
with the same petri dish. Simply warm it again until the crystals
disappear, and repeat the process.

8. Orally review the concepts taught.

Additional Activities Children can grow their own crystals and record their observations. Children can compare the growth rates of various crystals, and graph their results. Children can investigate the effects of light on various crystals. Children can investigate the properties of a variety of crystals. Additional References Brown and Forsyth, The Crystal Structure of Solids, Crane and Russak,
N.Y. 1973.

Holden and Singer, Crystals and Crystal Growing, Anchor Books,
Doubleday and Co. 1960.
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