What does chemistry study?
Everything is made of tiny atoms. Atoms join to form molecules. Chemistry asks: which atoms are here, how are they joined, and how can we change them?
A chemical reaction breaks old joins and makes new ones. The atoms stay the same. Only the partners change. Drag the slider in the 3D to see this.
Materials: plastics, metals, glass, fibres
Small molecules called monomers can join into a long chain called a polymer. Plastic bags, nylon clothes and pipes are polymers. Long chains make a material light, strong and easy to shape.
Other useful materials: alloys (a metal mixed with other atoms, like steel) and ceramics and glass (made from sand and clay at high heat).
The problem: many plastics do not rot. They stay for hundreds of years. So we need reduce, reuse, recycle and new materials that break down.
Medicine: the right shape for the job
A medicine is a molecule with a shape that fits a target in the body, like a key in a lock. A pain tablet, an antibiotic and a vaccine all work because of their shape or the message they carry.
Chemists first find a useful molecule (often from a plant or a microbe), then copy it in a lab, then test it for safety. Dose matters: the same chemical can heal in a small amount and harm in a large one. Always take medicine only as a doctor or the label says.
Food and farming: fertilisers and preservation
Plants need nitrogen to grow. Air is about four-fifths nitrogen, but it is locked in strong N2 molecules. In the Haber process, N2 and H2 are joined into ammonia (NH3), used to make fertilisers. This helped farms feed billions of people.
Too much fertiliser washes into rivers and causes algae to bloom. Food chemistry also gives us preservatives (salt, vinegar, sugar) that keep food safe for longer.
Energy and environment: fuels and their cost
A fuel such as methane (CH4) burns with oxygen: CH4 + 2 O2 → CO2 + 2 H2O. This reaction releases heat. But CO2 traps heat in the air and adds to climate change.
So chemistry also helps solve this: solar cells, batteries, and green chemistry that makes less waste. Good chemists do not only ask 'does it work?' but also 'is it safe and clean?'
Try it: spot the chemistry at home
Take a piece of paper and make three columns: material, medicine or health, food or energy. Walk around your home and write five things in each column that chemistry helped make. Then in the 3D, predict first: which change makes a long chain? Check by moving the slider.
Key formulas and definitions
- Key idea: atoms are never lost or made in a reaction, only rearranged.
- Plastic: many ethene (C₂H₄) molecules → one long chain (polymer)
- Fertiliser base: N₂ + 3 H₂ → 2 NH₃
- Fuel: CH₄ + 2 O₂ → CO₂ + 2 H₂O
- Key terms: atom, molecule, monomer, polymer, dose, preservative, green chemistry
Worked examples
1. 3 ethene molecules (C₂H₄) join into one chain. How many carbon and hydrogen atoms are in the chain?
Carbon: 3 × 2 = 6. Hydrogen: 3 × 4 = 12. The chain has 6 C and 12 H. The atoms are the same as before.
2. In N₂ + 3 H₂ → 2 NH₃, count the atoms on both sides.
Left: N = 2, H = 3 × 2 = 6. Right: N = 2 × 1 = 2, H = 2 × 3 = 6. Both sides have 2 N and 6 H, so no atom is lost.
3. Burning methane: CH₄ + 2 O₂ → CO₂ + 2 H₂O. How many atoms are on each side in total?
Left: 1 C + 4 H + 4 O = 9 atoms. Right: CO₂ has 3, and 2 H₂O have 6, so 9 atoms. The atom count is the same.
4. A medicine tablet is 500 mg. A doctor says to take 2 tablets a day. How many mg is that in 3 days?
In one day: 2 × 500 = 1000 mg. In 3 days: 3 × 1000 = 3000 mg (3 g). Never take more than the doctor says.
5. A plastic bottle is thrown away and not recycled. Give two ways to reduce this problem.
Reuse the bottle or carry a steel bottle (reuse), and send used plastic to recycling. Choosing materials that break down also helps.
6. A farmer uses double the fertiliser, hoping for a double crop. Why can this go wrong?
Plants take up only what they need. The extra washes into streams and feeds algae. The algae use up oxygen in the water and fish die. The crop also may not double.
Common mistakes
- Thinking chemistry is only about labs. Cooking, cleaning, farming and cars all use chemistry.
- Believing 'chemical' means 'harmful'. Water and salt are chemicals too. Safety depends on the dose and the use.
- Saying atoms are destroyed when something burns. They only move to new partners (like CO₂ and H₂O).
- Thinking natural is always safe and made-in-a-lab is always bad. Some natural things are poisonous and some lab medicines save lives.