5. Elements, Compounds & Molecules
GED® Science: Atoms, Elements & the Periodic Table (Deep Dive) · preview lesson
Atoms combine to make the huge variety of substances around us. Three words keep it straight.
- An element is a substance made of only one kind of atom (oxygen, gold, carbon). It can't be broken into simpler substances by chemical means.
- A compound is two or more different elements chemically bonded in a fixed ratio — like water (H₂O) or table salt (NaCl). A compound has new properties, different from the elements in it.
- A molecule is two or more atoms bonded together. It can be an element (O₂, two oxygen atoms) or a compound (H₂O).
A chemical formula shows the ratio of atoms: H₂O means 2 hydrogen atoms bonded to 1 oxygen atom.
⚠️ Common misconception: a compound's properties are not just a mix of its elements. Hydrogen and oxygen are both gases, yet bonded as water they form a liquid you can drink.
💡 Tip: element = one kind of atom; compound = different atoms bonded in a fixed ratio (with new properties).
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