Timothy Turner, age 11, of Twilight, West Virginia, for his question:

What is water made of?

Water is a chemical compound made of molecules, which are packages of chemical elements. The basic recipe calls for two atoms of hydrogen to one atom of oxygen.

When multiplied by about one zillion, we get enough water molecules to form a single drop of water. This chemical wonder is possible because of the numbers of electrons in atoms of hydrogen and oxygen.

Electrons form shells around the atomic nucleus, and the normal atom likes to have all of its electron shells complete. The hydrogen atom has only one electron and needs a second one to complete its lone shell. The oxygen atom has eight electrons. This gives it a complete inside shell, but two more are needed to complete a second shell, which requires eight. These mutual problems are solved when one oxygen atom and two hydrogen atoms share electrons. Together they form a molecule of water, in which each hydrogen atom lends and borrows an electron and the oxygen atom borrows two electrons to complete its outer shell.