CHEMISTRY · Stage 7 · Chapter 2: Elements, Compounds and Mixtures
Chemistry 2.2 Discovering the elements — Historical Chemistry
5 min read 7 parts Lesson 2 of 13
Lesson summary
2.2 Discovering the elements — Historical Chemistry — Alhussan International Academy — Chemistry (Stages 7–9) notes: Describe how knowledge of the elements developed from early ideas to modern chemistry and the factors that influenced when elements were discovered.Four elements —…
- Change of view
- Alchemists
- Phosphorus
- New elements
- Electrolysis
- Spectroscope
Part 1 of 7Early ideas about elements
- Four elements — more than 2000 years ago a Greek thinker suggested that everything was made from air, water, fire and earth.
- The idea was popular for hundreds of years.
- Scientists in India used it to help develop their ideas about atoms.
- Atoms — Democritus proposed that matter is made of tiny indivisible pieces, but these were ideas that could not be tested with the tools available.
- Change of view — from about 1700 scientists realised the four-element idea was wrong and looked for substances that could not be broken down into simpler substances.
- Boyle — in 1661 he defined an element as a substance that cannot be broken down into simpler substances by chemical means.
- Alchemists — they tried for centuries to change cheap metals into gold and failed, but developed methods still used today such as distillation and crystallisation.
Part 2 of 7The first discoveries
- Elements found on their own were discovered first.
- Early humans saw sulfur near volcanoes, made charcoal (a type of carbon) by burning wood and found gold in stream beds.
- Copper — it can exist on its own, but most is joined to other elements in rocks.
- People started extracting it from rock 7000 years ago for weapons, tools and jewellery.
- Bronze — people mixed copper with tin about 5000 years ago in the Indus Valley, and bronze is suitable for knives.
- Iron — people first extracted it from rock about 3500 years ago to make tools and weapons.
- Gold — a gold headdress over 4000 years old was found in a grave in Ur.
Part 3 of 71200 to 1700
- Zinc — it is not easy to get from its rock, but 800 years ago scientists in India obtained it by heating zinc-containing rock with other substances including soot and nuts.
- They made tens of thousands of tonnes.
- Phosphorus — Hennig Brandt made the first by evaporating water from urine, heating the remaining solid until red hot and collecting the phosphorus vapour.
Part 4 of 7The 1700s: elements from the air and more metals
- New elements — scientists discovered 17 new elements in the 1700s.
- Nickel was isolated from rocks and magnesium from pond water.
- Oxygen was separated from the air.
- Air — Henry Cavendish and Joseph Priestley removed oxygen from air to find out about the other gases, and Daniel Rutherford explained that air is mainly nitrogen.
- Lavoisier — he showed that burning is a reaction with oxygen, weighed substances before and after burning to show mass is conserved, and compiled a list of elements in the 1780s.
Part 5 of 7The 1800s: technology drives discovery
- ElectrolysisHumphry Davy used electricity to isolate reactive metals such as sodium and potassium in the early 1800s.
- Spectroscopethis new equipment helped scientists discover caesium and rubidium, and more than 50 elements were discovered in the 1800s.
- Aluminiumit was discovered in the 1800s, but not earlier because it is strongly joined to oxygen in its rock.
- Mendeleevin 1869 he organised the elements and predicted missing ones, when 63 were known.
Part 6 of 7Twentieth and twenty-first centuries
- Last gaps — they were filled in the 1920s when Ida Tacke and her colleagues discovered rhenium and technetium.
- Artificial elements — scientists made more than 25 in the twentieth century, produced by nuclear reactions in laboratories.
- Elements beyond uranium do not occur naturally in useful amounts.
- Today — there are 118 known elements.
| Period | Examples |
|---|---|
| Before 1200 | Copper, gold, iron, tin, zinc (in India) |
| 1200 to 1700 | Phosphorus (Brandt) |
| 1700s | 17 new elements including nickel, magnesium, oxygen |
| 1800s | Aluminium, caesium, rubidium and many reactive metals |
| 1920s | Rhenium and technetium and the last gaps |
Part 7 of 7Why history matters
- Technologyeach new method opened the door to elements that could not be found before.
- Evidencescientists build on earlier work, accurate data and repeated tests let others confirm results, and results are checked by peer review before an idea is accepted.
- Changescientific ideas are tested, shared and sometimes replaced.
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