Oxygen and nitrogen are examples of ______________.
An element is any substance that cannot be broken down into simpler substances. The smallest unit of an element is called an _________.
An element is made up of only _________ kind of atom.
Carbon dioxide is a _________ made up of the elements carbon and oxygen.
When two or more elements combine chemically, they form a(n) _________.
Most elements in living things occur in the form of compounds. The smallest unit of many compounds is called a(n) _________.
Water is another compound. Each water molecule is made up of _________ hydrogen atoms and one oxygen atom.