* Elements: Oxygen, carbon, and nitrogen are all fundamental building blocks of matter that cannot be broken down into simpler substances by chemical means.
* Molecules: Oxygen, carbon dioxide, and nitrogen exist as molecules, meaning they are made up of two or more atoms bonded together.
* Compounds: A compound is formed when two or more different elements chemically combine in a fixed ratio. For example, water (H₂O) is a compound because it is made up of two hydrogen atoms and one oxygen atom.
Summary:
* Oxygen (O₂): A molecule of two oxygen atoms.
* Carbon Dioxide (CO₂): A molecule of one carbon atom and two oxygen atoms.
* Nitrogen (N₂): A molecule of two nitrogen atoms.
They are not compounds because they consist of only one type of element.
