Elements, Compounds and Molecules
Elements are one kind of atom; compounds bond different kinds.
About this topic
An element consists of only one type of atom, such as oxygen or iron, and cannot be broken down chemically. A compound contains two or more elements chemically bonded in a fixed ratio, such as water (H2O) or carbon dioxide (CO2), and has properties different from its elements. A molecule is a group of two or more atoms bonded together; it may be an element, like O2, or a compound, like H2O.
The key idea is that chemical bonding changes properties. Sodium is a soft, explosive metal and chlorine is a poisonous gas, yet together they form sodium chloride, the harmless table salt on your food. A compound can only be split by a chemical reaction, such as passing electricity through water to get hydrogen and oxygen, whereas a mixture can be separated physically.
Chemical formulas record the composition: in CO2 the subscript 2 means two oxygen atoms for each carbon. Some elements exist as diatomic molecules: hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine. Compounds make up most of the world around us, from medicines to plastics.
Students often think all molecules are compounds, but O2 is a molecule of one element. Others assume ionic compounds like NaCl form molecules; they form lattices of ions instead, so we call NaCl a formula unit.
Key ideas
- Compounds have fixed ratios
- Molecules are bonded atoms
- Compounds break down only chemically
Quick check
Use cases: where Elements, Compounds and Molecules helps
- Homework: review the key idea behind Elements, Compounds and Molecules before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Elements, Compounds and Molecules without notes.
- Visual learning: play with the interactive lab to see how Elements, Compounds and Molecules changes when you adjust its inputs.
- Teaching a friend: explain Elements, Compounds and Molecules in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Elements, Compounds and Molecules?
Elements are one kind of atom; compounds bond different kinds.
What will I learn in Elements, Compounds and Molecules?
Compounds have fixed ratios. Molecules are bonded atoms. Compounds break down only chemically.
Is Elements, Compounds and Molecules part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Elements, Compounds and Molecules lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Elements, Compounds and Molecules?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.