1. ____ The first type is 2. an ____ , which is made of only one kind of atom. Familiar examples are the oxygen (O₂) in the air we breathe and copper (Cu) metal. The second type is 3. a ____ , which is a substance formed when two or more different kinds of atoms bond together. Common examples include water (H₂O) and carbon dioxide (CO₂). 4. A ____ is the process where these substances are transformed into new ones. Some reactions fizz, smoke and burn. Some happen very fast and strong—these can even 5. ____ ! compound

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