The Structure Of Crystals printable pdf download

High School Science

The Structure and States of Matter

Chemistry

Student Resource

Name: ___________________

The Structure of Crystals

Beautiful solids with regular, three-dimensional patterns have been prized for

thousands of years.

Choose one crystal to observe. Describe it in great detail, and then draw it.

Crystal Structure

A crystal is a solid in which the molecules are arranged in a three-dimensional repeating pattern.

Most solids are crystalline. Salt, sugar, ice, and diamonds are common examples of crystals.

Crystals come in a variety of geometric shapes. What are some of the shapes you saw when you

examined the crystal samples? When you looked at the salt crystals you should have seen little

cubes. If you were to examine snowflakes under a microscope you would see crystals in the

shape of hexagons. Sulfur crystals are in the shape of octagons. A crystal’s shape depends on the

arrangement of the particles within it.

There are seven crystal systems (or geometric shapes) into which all known crystals are

classified. The seven crystal systems are: cubic, tetragonal, hexagonal, rhombohedral,

orthorhombic, monoclinic, and triclinic. You can view a diagram of each of the systems at this

website: Click on the name of system to

view a graphic and information.

Some crystals are very large and can be seen with the naked eye. Some can be seen only with

special microscopes.

The shape and properties of a crystal depend on the atoms that make up the crystal and how

strongly the molecules are bonded together. In fact, there may even be different crystals of the

same substance. For example, diamond and graphite are two common forms of solid carbon.

Even though both crystals are made of carbon, their atoms are arranged differently. In diamond,

each carbon atom is strongly bonded to four others in a cubic lattice. In graphite, the carbon

atoms are packed more loosely in hexagonal layers with weak bonds between them. Graphite is a

dull, slippery solid with a low melting point. In contrast, diamonds are sparkly, have a high

melting point, and are very strong. Even though both crystals are made of carbon, they are very

different from each other.

Some crystals form naturally in the earth, and have taken thousands or millions of years to grow.

Some form as hot solutions of chemicals or molten rock (lava) cool deep within the earth.

November 11, 2002

SCoPE SC100108 Page 1 of 3

The Structure Of Crystals