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Period: 500 BCE to
Timeline of the Models of Matter
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450 BCE
Empedocles
Empedocles was a Greek philosopher who believed that all matter was made up of a mixture and ratio of the "elements": earth, water, fire and air. He called his model the "four-element model". Through his experiments, he found that although air is invisible, it takes up space and is some form of matter and not just "nothing". His discoveries and his model are important because he gave the idea that matter is composed of four elements and that air is a form of matter. -
400 BCE
Democritus
Democritus was a Greek philosopher who believed that all matter was composed of small particles (atoms) that are indivisible. He called them "atomos". He believed that different elements had a different and unique type of atom. He experimented with breaking down a seashell until it was a powder. His ideas were rejected by influential figures and ignored by society. His discoveries are important because he introduced the idea of spherical small particles (atoms) that make up matter. -
350 BCE
Aristotle (advice for importance)
Aristotle rejected Democritus' idea of atoms because he thought that it didn't make sense. He instead believed in Empedocles' four-element model and that all substances and matter were made up of a mixture of earth, water, fire and air. He did not do any experiments to prove his beliefs, he simply believed in the four-element model. Because of his influence, many people accepted the four-element model of matter. The idea of atoms was ignored for about two thousand years. -
500
Many Alchemists (500-1600 A.D.)
Alchemists believed that they could create gold out of cheap metals and tried but failed to prove it. They created symbols for substances (elements and compounds). Alchemists created equipment and tools for the science laboratories such as filters, beakers, etc. They discovered many new substances yet they still believed in the four-element model. Their work is important as they created laboratory equipment and chemical symbols for elements and compounds. -
Robert Boyle
Robert Boyle didn't accept the four-element model. After his experiments with gases, he concluded that air is a mixture and not an element. He believed that the only way to explain his results was with the idea of small particles (atoms). He defined elements as pure substances that cannot be broken down any further. His work is important because he proved that air is a mixture and not a pure substance and he defined an element. -
Joseph Priestley (late 1700s)
Joseph Priestley was an English scientist. He became the first to separate, contain and discover a gas which is now known as the element oxygen. He experimented with mercury oxide and burning glass and discovered oxygen as a result of this experiment. He also found that plants and trees produce oxygen through his other experiments. His work is important because he discovered the element oxygen, how it can be produced and he described some of its properties. -
Henry Cavendish (late 1700s)
Henry Cavendish discovered a gas that is now known as the element "hydrogen" by mixing metals with acids and producing a light and flammable gas. He didn't know that he discovered the element hydrogen. He also experimented with oxygen and his gas (hydrogen) by burning his gas in a jar with oxygen. He proved that water isn't a pure substance since it was the result of the reaction between the two gases. His work is important because he discovered hydrogen and proved that water wasn't an element. -
Antoine Lavoisier (late 1700s)
Antoine Lavoisier experimented with Priestly's gas and discovered that it was an element and he named it "oxygen". He also discovered that air was a mixture of at least two gases and one of them had to be oxygen. Lavoisier found that oxygen was a very important part of combustion as combustion required oxygen. His work is important because he named the element oxygen, he found that oxygen was important in combustion and that air was a mixture of gases. -
John Dalton
John Dalton created a theory of why elements are different from other elements and from non-elements. His atomic model stated that all matter is made of very small particles called atoms, elements have their own unique atom and mass and compounds are chemically-bonded atoms from different elements. It also states that atoms are indestructible, uncreatable and indivisible in chemical changes. He made a new idea of atoms and their nature/structure and explained why elements differ from each other. -
Michael Faraday (1800s)
Michael Faraday experimented and found that electrical currents could chemically change some compounds in a solution. He also found that atoms become ions by obtaining electrical charges. His model stated that all matter has positive and negative charges, same charges repel and opposite charges attract and atoms form molecules by their electrical attraction. His work is important because he introduced the idea of charges of atoms and how they function. -
J.J. Thomson
J.J. Thomson discovered electrons (light and negative particles). He discovered them by experimenting with beams of protons. His model was called the "raisin bun model". His model stated that all atoms have electrons which are negatively-charged and small in mass. It also says the atom is a positively charged sphere with electrons within it which makes the resulting atoms uncharged or neutral. His work is important because he discovered electrons and introduced their function/structure. -
Hantaro Nagaoka (1903-1904)
Hantaro Nagaoka had a different idea of atoms than Thomson. He believed that the atom was a positively charged sphere with a ring of negative electrons surrounding it. He called it the "saturnian model". He didn't do any experiments to prove his model or theory, he assumed what an atom looked like. His work is important because it gave a different perspective and idea of what the structure of atoms and electrons might look like. -
Ernest Rutherford
Ernest Rutherford aimed alpha particles at gold foil to test the theories and models of Thomson and Nagaoka. He expected the alpha particles to pass through the foil but a few alpha particles bounced off of the foil. He made his model and named it the "nuclear model". It stated that an atom has a small positive core called the nucleus that is surrounded by mostly empty space with negative electrons moving quickly. His work introduces the nucleus and gives more details on atoms. -
Niels Bohr
Niels Bohr made a new model of the atom based on Rutherford's model. He suggested that electrons move around the nucleus in "shells" which are basically circle-shaped orbits. He also suggested that electrons that are in one shell can only move in that shell. His work is very important because it gives more insight into how electrons function in an atom and the structure of atoms and electrons.
