GRADES 5-8
GROWING CRYSTALS

BACKGROUND INFORMATION: Solids, Liquids And Gases In this activity you grew your own crystals. However, you might be wondering what a crystal is and how it is formed? Objects on earth can be classified as a solid, a liquid or a gas. A substance like water can exist as a solid, liquid and a gas. Water commonly exists as a liquid. The gas form of water is called steam or water vapor and the solid phase is called ice. A block of ice is a solid, so is a pebble. The molecules are spaced closely together forming specific patterns. If an ice rod is placed in a square hole, the ice does not change its shape to match the square hole. No matter how hard it is squeezed or pulled, the molecules do not move closer together or further apart. The object may break, but the molecules don't move. When a substance is in a solid state, its molecules are all lined up and rigid. Its volume and shape are fixed. When water is poured from a round container into a square one, the water will not retain its round shape. The water is a liquid. The liquid takes the shape of the square container. The liquid will not expand to fill a larger space. It cannot be made smaller by squeezing or pulling. The molecules do not move closer or further apart. Gases take the shape of their containers, and expand or contract to fill the container. When a person takes a breath of air, air rushes down the bronchial tubes and tries to fill all the spaces in the lungs. A big breath makes it easier to feel the lungs expand, but a small breath fills ALL of the lungs, too. A gas can be expanded or compressed. The molecules can move closer or farther apart. Crystals Crystals have been studied for hundreds of years. Crystals can be found in nature, can be grown and are also manufactured. Crystals like diamonds or other gems are used as jewelry or for their beauty and appearance. Crystals also are used in numerous high technology industries. Solar cells, transistors (layers of semi-conductors) and the LCD (liquid crystal device) displays are used on your clocks, calculators and many high tech instruments. Crystals are bodies formed as a substance solidifies (becomes solid). Inside of a crystal its atoms have a regular repeating arrangement. Externally (outside on its surface) crystals often have plane (flat or level) faces. Examine the pictures of salt and rock candy. You can see the salt's surfaces form small cubes as well as the level surfaces on the rock candy. Salt And Rock Candy Crystals Although the crystal faces can be seen on the rock candy, many crystals are too small to be seen without a microscope. Many substances are made of thousands of tiny crystals. You may be surprised to learn that metal is composed (made up) of crystals. You can see the flat faces of these crystals. Much of the beauty of crystals is due to the faces. However, since the faces can be ground off or destroyed, external (outer surface) faces are not critical and necessary for an object to fit the definition of a crystal. For that reason, to be classified as a crystal the atoms (the smallest, most minute particle of any element) must form a regular repeating pattern. For example, snowflakes are crystals of snow. (Snow is made of white crystals of frozen water.) All snowflakes form a hexagon (a closed shape having 6 sides and angles). Liquid crystals are liquids which have some of the characteristics of a solid. At the atomic level the structure of the liquid crystal retains the regular repeated pattern of a solid crystal. REFERENCES: Sands, Donald E., Introduction To Crystallography, Dover Publications, New York, 1975. Van Wagner, Lois, Crystals: More Than Meets the Eye, http://www.yale.edu/ynhti/pubs/A5/vanwagner.html, Yale-New Haven Teachers Institute, 1997.