Defining Molecule vs. Compound
A molecule is any particle made of two or more atoms chemically bonded together. A compound is a specific type of molecule that consists of two or more *different* elements bonded together. The key difference is that compounds must have different elements, while molecules do not.
The Core Distinction: Composition
The main rule to remember is: all compounds are molecules, but not all molecules are compounds. This is because the definition of a molecule is broader, simply requiring multiple atoms. A compound has the additional requirement that these atoms must come from at least two different elements on the periodic table.
Section 3: A Practical Example
An oxygen molecule (O₂) consists of two oxygen atoms bonded together. Since it's made of only one element, it is a molecule but *not* a compound. A water molecule (H₂O) consists of two hydrogen atoms and one oxygen atom. Because it contains different elements (hydrogen and oxygen), it is both a molecule *and* a compound.
Section 4: Why This Distinction Matters
Understanding this difference is fundamental to chemistry because it helps classify substances and predict their properties. Compounds have unique chemical and physical properties that are distinct from their constituent elements. For example, the properties of water (H₂O), a compound, are completely different from those of hydrogen and oxygen gases, which are elemental molecules.