Elements & Compounds
🟡 Atoms: The Basic Unit of Matter
An atom is the smallest particle of an element that still keeps the properties of that element. You can’t see atoms with your eyes, but they’re everywhere! Everything is made of atoms.
When atoms join together, they can form molecules.
💡 Think of atoms like LEGO bricks — one brick on its own is an atom. Put a few bricks together? You’ve got a molecule!
Elements: Pure Substances
An element is a pure substance made of only one kind of atom.
Examples include:
Hydrogen (H)
Oxygen (O)
Helium (He)
Copper (Cu)
Even if there are two atoms of the same element joined together (like O₂), it's still an element — because all the atoms are the same.
🧪 Compounds: New Substances Formed
A compound forms when two or more different elements are chemically joined together. The atoms bond, and the new substance has different properties than the elements it came from.
Examples:
Water (H₂O) → made from hydrogen and oxygen
Carbon dioxide (CO₂)
Glucose (C₆H₁₂O₆)
Sulfuric acid (H₂SO₄)
Compounds have fixed formulas, and they can only be separated by chemical reactions.
🧂 Mixtures: A Bit of Everything
A mixture is when two or more substances (elements or compounds) are physically combined, but not chemically bonded. This means:
They can often be separated easily (by filtering, evaporation, etc.).
Each part keeps its own properties.
Examples:
Air (a mix of gases)
Saltwater
A nuts mixture (yum!)
🖼️ Recognising Atoms, Molecules, and Mixtures
In diagrams, you might see:
A single circle: usually an atom
Two of the same circles joined: a molecule of an element (e.g., O₂)
Different circles joined: a molecule of a compound (e.g., H₂O)
Different molecules or atoms all mixed together: a mixture
Key Differences to Know
Concept | What It Is | Key Feature |
Atom | Smallest particle of matter | Can exist alone or in groups |
Element | Only one kind of atom | Pure substance |
Molecule | Two or more atoms joined | Can be the same or different atoms |
Compound | Molecule with different atoms chemically joined | Forms a new substance |
Mixture | Substances together but not chemically bonded | Can be separated easily |
🎯 Top Tips
🌟 An element = only one type of atom.
🌟 A compound = different atoms chemically joined.
🌟 A mixture = substances together but not chemically bonded.
🌟 O₂ is a molecule of an element, but H₂O is a compound.
🌟 Look for visual clues: Same atoms = element, different joined atoms = compound, jumbled atoms = mixture.
🌟 Compounds have fixed formulas. Mixtures don’t!
🌟 You can separate mixtures easily, but not compounds.