What is chemistry?
Chemistry is the study of substances (the materials around us), what they are made of, how they behave and how they change into other substances.
A change that makes a new substance is a chemical change (burning, rusting, cooking). A change that does not is a physical change (melting ice, tearing paper).
A short history
- Ancient crafts. People made copper and iron, glass, pottery, soap, dyes and medicines. India, Egypt, China and Mesopotamia all had skilled crafts.
- Alchemy. Alchemists tried to turn cheap metals into gold and to find a drink for long life. They did not succeed, but they invented flasks, distillation and many tests.
- Careful weighing. In the 1700s, Antoine Lavoisier weighed everything before and after a reaction in a closed jar and showed mass is kept. He also showed what burning really is: a substance joining with oxygen.
- Atoms. In the early 1800s, John Dalton suggested that matter is made of atoms. Later, chemists found the periodic table, which sorts the elements.
- Today. Chemistry helps make medicines, plastics, fuels, fertilisers, materials and clean energy.
Methods of chemistry
- Observation: look, smell (carefully, never sniff directly), listen, measure.
- Experiment: change one thing at a time and keep everything else the same.
- Measurement: use a balance for mass, a cylinder for volume, a thermometer for temperature.
- Model: draw atoms and molecules to explain what we cannot see.
- Record and share: write results so others can repeat the test.
Safety first: wear goggles, never taste chemicals and follow the teacher.
The language of chemistry
Chemists use one set of short signs in every country.
- Symbols for elements: H (hydrogen), O (oxygen), C (carbon), Na (sodium), Fe (iron). The first letter is capital, a second letter is small.
- Formulas for compounds: H2O (water), CO2 (carbon dioxide). The small number is how many atoms of that element.
- Equations show change: iron + oxygen gives iron oxide.
Sources of information
Where do you find correct chemistry facts?
- School textbooks and your teacher.
- Encyclopedias and science museums.
- Scientific magazines and reports of research institutes.
- Websites of universities and science organisations.
Check a fact in at least two good sources. Ask: who wrote it, when, and can the result be repeated?
Try it
Use the slider on the timeline in the 3D. Then try this at home with a grown-up: weigh a bottle with vinegar and a pinch of baking soda inside a closed balloon on the neck. Mix and weigh again. Does the mass change? (Hint: Lavoisier.)
Key formulas and definitions
- Chemistry = study of substances, their changes and uses
- Mass before = mass after (closed system)
- Symbol: H, O, C, Na, Fe. Formula: H₂O, CO₂
- Method: observe → question → experiment → conclude → share
Worked examples
1. Is rusting of an iron nail a physical or chemical change? Why?
Chemical. A new substance, rust, forms and it is not iron any more.
2. What did Lavoisier prove with a closed jar and a balance?
That the total mass before and after a chemical change is the same, so matter is not lost.
3. Read the formula CO₂. What does it tell you?
A molecule of carbon dioxide has one carbon atom and two oxygen atoms.
Common mistakes
- Thinking chemistry is only about labs. Cooking, cleaning and farming use chemistry too.
- Writing symbols wrongly: CO is carbon monoxide but Co is cobalt. The capital and small letters matter.
- Believing alchemy was just foolish. It built tools and methods that later became chemistry.
- Tasting or sniffing chemicals to identify them. Never do this.