What Are Elements, Compounds and Mixtures?
Chemistry begins with three building blocks: elements (pure substances made of one type of atom), compounds (pure substances where atoms bond chemically), and mixtures (two or more substances physically combined). Understanding these distinctions is key to all chemistry.
Elements are pure substances containing only one type of atom. Compounds are pure substances formed when elements bond chemically. Mixtures are two or more substances physically blended — they are not chemically bonded.
- •Pure substance (one type of atom)
- •Fixed composition
- •Examples: oxygen (O₂), iron (Fe), carbon (C)
- •Cannot be broken down by physical means
- •Pure substance (atoms chemically bonded)
- •Fixed composition
- •Examples: water (H₂O), salt (NaCl), sugar (C₁₂H₂₂O₁₁)
- •Requires chemical reaction to separate
Step-by-step worked examples
Pure water (H₂O) is a compound. Name the elements it contains.
Water is made of hydrogen and oxygen atoms bonded together. Elements: Hydrogen (H) and Oxygen (O)
Salt water is a mixture. Name the compound and the element/solvent.
Salt water = salt (NaCl, a compound) + water (H₂O, a compound) The solvent is water; the solute is salt.
Air at sea level contains ~78% nitrogen gas (N₂) and 21% oxygen (O₂). Is it an element, compound, or mixture?
Air contains two different gases (N₂ and O₂) physically mixed. Air is a mixture.
Flashcards
Quick quiz
Q1.Which is a pure substance?
Q2.Rusting iron (iron oxide, Fe₂O₃) is a(n)…
Q3.How do you separate salt from salt water?
Q4.Which can be separated by filtration?
The full card deck, worked steps and AI-tutor support for “What Are Elements, Compounds and Mixtures?” are in Notek — study by hand before your exam.
Common mistakes
Thinking mixtures are impure substances. — Correct: Mixtures are still pure; they are just not chemically bonded.
Confusing compounds with elements. — Correct: Compounds are made of two or more elements bonded together.
Believing you can separate compounds physically. — Correct: You need a chemical reaction to break compound bonds.
Thinking air is a single element. — Correct: Air is a mixture of gases (mostly N₂ and O₂).
FAQ
What is an element in chemistry?
A pure substance made of only one type of atom. Examples: hydrogen, oxygen, carbon, iron.
What are compounds? Give examples.
Pure substances where two or more elements are chemically bonded. Examples: water (H₂O), salt (NaCl), sugar (C₁₂H₂₂O₁₁).
Can you separate a mixture?
Yes — by physical methods like filtration, evaporation, distillation, or magnetism.
What is the difference between a compound and a mixture?
Compounds are chemically bonded (fixed ratio); mixtures are physically combined (variable ratio).