Theories of Matter Throughout History

Events

Stone Age Chemists

Approx. 8000 B.C - Approx. 6000 B.C

*The first chemists lived before 8000 B.C in an area now called the Middle East.
*This period is known as the Stone Age because humans only used simple stone tools at the time.
*Metals had not been discovered yet
*These chemists learned how to start and control fire, resulting in being able to change the range of substances to their advantage.

Early Chemists Investigating Metallurgy and Liquids

Approx. 6000 B.C - Approx. 1000 B.C

*Early chemists investigated only materials that had high value to humans
*Metals such as gold and copper
*Copper could be used to make pots, coins, tools and jewellery
*Discovered that when copper is heated it becomes very useful because it can be rolled into sheets or be stretched into long wires
*Gold could be made into detailed designs, formed into wire, beat into sheets, and could not be made into weapons

Early Chemists

Approx. 4500 B.C - Approx. 1200 B.C

*Experimentation with copper around 4500 B.C led to the creation of hard, strong material known as bronze, which is produces when copper and tin are heated together
*Many cultures investigated in ways of extracting and using different types of liquids
*Juices and oils were especially important both in everyday life and in rituals

Iron Age

Approx. 1200 B.C - Approx. 500 B.C

*Around 1200 B.C a group of people in the Middle East called Hittites discovered how to extract iron from rocks and turn it into a useful material
*Chemists learned to combine iron with carbon to produce an even harder and stronger material, steel
*Steel could be used to make sharper blades that could be fashioned for hunting
*Steel could be used to build stronger armour to protect soldiers in battle

Early Ideas About the Composition of Matter

Approx. 500 B.C - Approx. 350 B.C

*Ideas that all matter is made up of particles started
*Greek philosophers observed that a rock could be broken into smaller and smaller pieces until it became a powder
*Greek philosophers wondered how many times you could break the particles of powder down until they couldn't be broken down any more

Democritus

Approx. 500 B.C

*Democritus used the word 'atomos' to describe the smallest particles that could not be broken down any further
*Atomos means 'indivisible'
*He stated that each type of material was made up of different types of 'atomos'
*He believed these different particles gave each material its own set of unique properties, and by mixing different 'atomos' you could make different materials with their own unique properties

Aristotle

Approx. 350 B.C

*Aristotle stated that everything was made up of earth, air, fire, and water
*Since Aristotle was well known and well respected, his description of matter was preferred over that of Democritus for about 2000 years

Alchemists

Approx. 350 B.C - Approx. 1500 A.D

*For about 2000 years after Democritus's time, experiments with matter were mainly carried out by alchemists, people who believed it should be possible to change metal into gold
*Alchemy - Arabic word al-kimiya, translates to "the chemist"
*Alchemy is considered a pseudo-science, not real science, because it includes the use of 'magic'
*During this time, although alchemy isn't considered a science, many useful tools were developed that we use in labs today, and other practical discoveries were made as well:
-beakers and filters
-plaster of Paris
-how to prepare chemicals such as hydrochloric acid
*Andreas Libau, a German alchemist, published Alchemia, the first chemistry text ever printed

Robert Boyle

1660

*Experimented with the behaviour of gasses
*Interested in what happened when gasses were put under pressure as well as determining the composition of gasses and other substances
*Convinced that matter was made up of tiny particles, group together in different ways to form individual substances, similar to the beliefs of Democritus
*Felt the purpose of chemistry was to determine the types of particles each substance was made up of

Antoine Laurent Lavoisier

1770 - 1780

*Studied chemical interactions
*Developed a system for naming chemicals
*Defined some of the substances discovered to his time, including hydrogen, oxygen, and carbon
*Called the "Father of Modern Chemistry"
*After his execution, his wife Marie, who had previously worked as his lab assistant, continued his work

John Dalton

1808

*Developed his own theory of the composition of matter, that matter was made up of elements
*First to define elements as pure substances that contained no other substances like gold, oxygen, chlorine, and stated that each element is composed of a particle called an atom
*Put forward the first modern theory of the atomic structure, the "billiard ball model"
*He stated atoms in a particular element are identical in mass, and no two elements have atoms of the same mass

J.J Thomson

1897

*First person to discover a subatomic particle, electrons
*Experimented with cathode rays, concluding that the rays were made of streams of negatively charged particles, smaller in mass that even a hydrogen atom
*Proposed the "raisin bun model" of the atom that described the atom as a positively charged sphere in which negatively charged electrons were embedded like raisins in a bun

Ernest Rutherford

1898 - 1907

*Won a Nobel Prize in 1908
*Conducted experiments in which he shot positively charged particles through a thin gold foil
*His results showed that while most particles behaved as he predicted, that all the high speed particles would pass straight through the foil without being effected by the gold atoms, some other particles were greatly deflected
*Suggested that atoms were mainly empty space through which the positive particles could pass, but at the core was a tiny positively charged center, which he called the nucleus
*Calculated that the nucleus was 1/10,000 the size of the atom

Hantaro Nagaoka

1904

*Refined Thomson's model of the atom
*His model resembles a miniature solar system, at the center a large positive charge with negatively charged electrons orbiting around it, similar to planets orbiting the sun

Niels Bohr

1913

*Suggested that electrons do not orbit randomly in an atom, instead they move in specific circular orbits, or electron shells
*Believed that electrons jump between these electron shells by gaining or loosing energy

James Chadwick

1932

*Discovered that the nucleus contains positively charged particles called protons, and neutral particles called neutrons

Quantum Mechanics Model

present

*Research in the area of quantum mechanics found that the structure of the atom is different from Chadwick's model
*The quantum mechanics model describes electrons as existing in a charged cloud around the nucleus