In short: Chemistry is the study of matter and how it changes. Matter is anything that has mass and takes up space, so heat, light and sound are not matter, and chemists study it through experiments that give qualitative (word) and quantitative (number) data.
Chemistry is the study of matter
Chemistry is the study of matter: what it is made of, how it behaves, and how it changes.
Matter is anything that has mass and takes up space (has volume). Air, water, your desk and your body are all matter.
Some things are not matter, because they have no mass and take up no space: heat, light, sound and thoughts. These are forms of energy or ideas.
Everything made of matter is built from tiny particles called atoms. A chemical is any substance with a fixed make-up, such as water, salt or oxygen. Everything you can touch is made of chemicals.
Mass and weight
These two words are often mixed up in everyday life, but in science they mean different things.
| Mass | Weight | |
|---|---|---|
| What it is | The amount of matter in an object | The pull of gravity on that matter |
| Unit | kilogram (kg) or gram (g) | newton (N) |
| Measured with | A balance | A spring scale |
| Changes with location? | No | Yes |
An astronaut with a mass of 70 kg has a mass of 70 kg on Earth, on the Moon and in space. On the Moon, gravity is weaker, so her weight is only about one sixth of her weight on Earth.
What chemists look at
Chemists ask four kinds of questions about matter.
| Area | Question | Example |
|---|---|---|
| Composition | What is it made of, and in what amounts? | Water is 2 hydrogen atoms to 1 oxygen atom |
| Structure | How are the atoms arranged in space? | Diamond and graphite are both carbon, arranged differently |
| Properties | What is it like? | Copper is shiny, bendy and conducts electricity |
| Reactions | What happens when it meets other chemicals? | Iron rusts in wet air |
How science builds knowledge
Chemists collect two kinds of data.
- Qualitative data describes qualities using words: "the solution turned blue", "it smells like rotten eggs".
- Quantitative data uses numbers and units: "the mass is 4.2 g", "the temperature rose by 12 °C".
Over time, observations grow into bigger ideas.
| Word | Meaning | Example |
|---|---|---|
| Hypothesis | A testable prediction | "If I heat the water, more sugar will dissolve" |
| Model | A picture, diagram or idea that explains something we cannot see directly | The Bohr model of the atom |
| Theory | A well-tested explanation of why things happen, supported by lots of evidence. It can change if new evidence appears | Atomic theory, kinetic particle theory |
| Law | A statement of what always happens, often as an equation. It does not explain why | The law of conservation of mass |
Research and technology
- Pure research seeks knowledge for its own sake. "What elements are in this new orange?"
- Applied research solves a specific problem. "Can a chemical from this orange shorten a cold?"
- Technology is the practical use of scientific knowledge to make products or tools. A drought-proof orange tree made by changing its genes is technology.
The branches of chemistry
| Branch | Studies | Example |
|---|---|---|
| Organic | Compounds that contain carbon (the chemistry of living things, fuels and plastics) | Making a new medicine |
| Inorganic | Substances that mostly do not contain carbon | Metals, minerals, salts |
| Physical | Energy, rates of reaction and how matter behaves | How fast a battery discharges |
| Analytical | What substances are present and how much | Testing water for lead |
| Biochemistry | Chemistry inside living organisms | How enzymes digest food |
A very short history
- Ancient times: people used fire, made pottery, smelted metals and made dyes and medicines, without understanding why they worked.
- About 2500 years ago, Greece: philosophers such as Aristotle believed everything was made from four "elements": earth, water, air and fire. Democritus suggested matter was made of tiny particles he called atomos, meaning "cannot be cut". They used reasoning, not experiments.
- The Middle Ages: alchemists tried to turn cheap metals such as lead into gold and searched for an "elixir of life". Their work was secret and not tested properly, so it was a pseudoscience (false science). But they did invent useful lab equipment and methods.
- From the 1600s: scientists such as Robert Boyle began using the scientific method: careful experiments, measurements, and sharing results so others could check them. Modern chemistry was born.
- Has mass and volume
- Made of atoms
- Not matter: heat, light, sound
- Mass: amount of matter
- Weight: pull of gravity
- Qualitative and quantitative
- Model, theory, law
- Pure vs applied research
- Organic, inorganic
- Physical, analytical
- Biochemistry
- Greek four elements
- Alchemy
- Scientific method
Quick summary
- Chemistry is the study of matter and how it changes.
- Matter has mass and takes up space. Heat, light and sound are not matter.
- Mass is the amount of matter (kg). Weight is the pull of gravity on it (N) and changes from place to place.
- Qualitative data uses words. Quantitative data uses numbers.
- A theory explains why. A law describes what always happens.
- Pure research seeks knowledge. Applied research solves problems. Technology uses science to make things.
- Five branches: organic, inorganic, physical, analytical, biochemistry.
Quiz
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Chemistry is the study of:
- A Living things only
- B Matter and the changes it undergoes
- C Stars and planets
- D Forces and motion only
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B: Matter and the changes it undergoes
Chemistry studies what matter is made of and how it changes.
Matter is anything that:
- A Can be seen
- B Has mass and takes up space
- C Gives off light
- D Is a solid
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B: Has mass and takes up space
Air cannot be seen, but it is still matter because it has mass and volume.
Which of these is NOT matter?
- A Smoke
- B Air
- C Heat
- D Water
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C: Heat
Heat is a form of energy. It has no mass.