Each substance has a unique set of properties that depends on the kinds of atoms it has and how the atoms are connected, or bonded. Bonding is related to the electrons in an atom, and there are different kinds of bonds. As a result, some substances can have the same atoms but different bonds. Substances that are different but have the same atoms are called allotropes. Allotropes have very different properties. Diamond and graphite are well-known allotropes. Graphite is used in pencils for writing and is sometimes called lead. Diamond is colorless and transparent, and is one of the hardest substances known. Graphite is dark gray and soft. When we write, layers of graphite easily transfer from the pencil to the paper. Although they’re different, diamond and graphite each only contain one kind of atom—carbon.

How do you think the bonds between carbon atoms might be different in diamond and graphite? Use household materials to build physical models to help you develop your ideas. Describe what you learned from your models. What other kinds of allotropes are there? What kinds of properties and atomic bonds do they have?