Snowflakes originate from countless water molecules that initially come together in small groups as a result of a weak attractive force between oxygen and hydrogen atoms. The same forces subsequently organize the groups into a frozen molecular crystal, a perfectly organized lattice of molecules. Finally, several molecular crystals join to form a snowflake. Scientists have realized for sometime that the force that assembles molecules into natural crystal can be utilized to produce a variety of important materials. They have determinate the structure of more than 90,000 molecular crystals, the most common examples are aspirin and mothballs.
In recent years, researches have study how molecules organize themselves to form crystals in the hope of better understanding why molecules and what conditions will produce molecular crystals with unusual and useful proprieties. Scientists are sure that the material proprieties of a crystal depend in large part on the organization of the molecules in the crystal, yet they know little about the factors controlling the assembling of such crystals.
Synthesizing a molecular crystal is similar to designing a building. Before construction can begin, the architect specifies the shapes and sizes of the girders and the numbers and placement of the rivets. Similarly, to produce new molecules of crystals, chemists must choose molecules of the appropriated sizes and shapes and select the molecular force that we hold the crystal together. A chemist can normally find many molecules of various shapes and sizes but the challenge is to find once that assemble in a predictable form.