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450 BCE
Empedocles's proposed Theory
A Greek Philosopher named Empedocles believed that all matter was made up of four elements: Earth, Air, Water, and Fire. These Elements could be mixed to create different substances for example volcanic rock could be 2 parts earth one part fire. Unlike other Philosophers of his time Empedocles actually used experiments to prove his theory. He knew that Air was an element because it took up space it wasn't just nothing. -
400 BCE
The Proposal of Atoms
Another Greek named Democritus proposed the theory that all matter was made up of tiny particles, he believed that these particles could not be broken down. He called these particles Atoms, named after the greek word atomos (which translates to Invisible). He thought that elements were made up of many different atoms (A revolutionary idea for the time). Unfortunately this theory was dismissed because Socrates (an important figure at the time) never accepted Democritus's Ideas. -
350 BCE
Approval of Empedocles Theory
Aristotle a Philosopher from the time approved of Empedocles's four element theory despite the existence of Democritus's much more modern theory of Atoms. Aristotle had so much influence that his writings caused the four elements theory to be accepted for almost 2000 years. -
Period: 500 to
Metal Growth?
From 500-1600 AD many alchemists believed that metals grew into gold as if they were plants. Many Experiments were conducted attempting to turn cheap metals to gold. They also created chemical symbols for things we now recognize as elements or compounds, some laboratory tools we use today are invented during this time such as beakers or filters. Despite all this they still believed in the four element theory. -
Modern Elements
Robert Boyle, an english scientist finally denied the four elements theory. He came up with a new definition for the word element, "I mean by element simple unmitigated bodies." this definition is still used today. He basically means that an element is a Pure Substance that cannot be chemically broken down into simpler substances. Boyle also thought that air wasn't an element rather a mixture (which is also true). -
The Discovery of Hydrogen
Henry Cavendish (an English Chemist) experimented by mixing iron and zinc in Hydrochloric, and Dilute Sulfuric acids. This caused a gas that was lighter than air to be released. In about 10 years he would use Joseph Priestly's oxygen and his gas would produce water when burnt. Cavendish didn't know it at the time but he had created Hydrogen, what he did know was that water wasn't an element instead it was a compound (because when Oxygen and Hydrogen were burnt together water was produced). -
The Discovery of Oxygen
During the late seventeen hundreds two scientists made essential discoveries about our air. Firstly, Joseph Priestly (a english chemist) managed to isolate oxygen scientifically, at the time Joseph did not know that he had discovered an element. This would be discovered by Antoine Lavoisier (A french chemist who is regarded as the father of modern chemistry). Antoine also experimented with the isolated oxygen, he concluded that Air was a mixture with two or more gases, one of which was Oxygen -
John Dalton's Atomic Model
In 1808 the existence of elements was generally agreed upon. An English Chemist named John Dalton took the existence of elements and built upon it, he proposed a theory about how and why elements differ from each other and non elements. he also made an atomic model to help prove his theory. His Atomic model stated all matter is made up of atoms, each element has it's own atoms, compounds form when atoms of different elements link into molecules, and atoms cannot be created in chemical changes -
Dalton's Updated Atomic Model
Dalton's atomic model accounted for many things but he couldn't explain static electricity, to fix this he came up with a theory and an updated atomic model to go along with it. His new model showed tiny negatively charged particles, these particles could be removed from their atoms and moved onto another. The exact date for these events is hard to find but 1820 is close -
An Electrical Discovery
Michael Faraday an english scientist discovered that electric currents could cause chemical change in some compounds. He believed Atoms in these compounds can gain electrical charge/be transformed into ions. This discovery also changed dalton's atomic model in some way these are: Matter must contain both a positive and negative charge, Negative charges attract positive charges and the other way around, and When atoms merge they become molecules due to the electrical attraction between atoms -
Further Changes to the Dalton's Atomic Model
70Years later a English Physicist named JJ Thomson changed Dalton's Atomic Model even further. Thomson had recently discovered Electrons which are very small negatively charged particles. These changes to Dalton's model would cause this version to be known as the raisinbun model, these changes were: All atoms contain electrons, Electrons have a small mass and are negative, Everything else in the Atom is positive, The electrons are embedded in the sphere causing any resulting atoms to be neutral -
The Nuclear Model Pt. 2
Rutherford's Nuclear Model has a few differences from the Raisin Bun Model such as: Atoms in the Nuclear Model have a small positive core called a Nucleus, and this Nucleus is surrounded by primarily empty space with fast moving negative electrons. -
The Nuclear Model
Ernest Rutherford a British physicist who was working at McGill University in Montreal wanted to test the Raisinbun Model, He aimed Alpha particles (a type of radiation) at a sheet of golden foil. If Thomson's Model was correct the particles would pass right through, what happened is that most went through but some confusingly bounced back. This amazed Rutherford who wasn't expecting such a strange outcome. in order to explain this strange outcome he made a new atomic model, the Nuclear Mode
