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450 BCE
The Four Elements
A Greek scholar, Empedocles, realized that matter was made up of four elements, which include fire, water, earth and air. When these elements were mixed together, they created different substances. To conclude that air was one of the four elements, he experimented to discover even though air is invisible it is not "nothing" and contains particles. -
400 BCE
Discovering Particles/Atoms
Democritus (a Greek), thought that matter was made up of tiny particles which he called atoms (after a Greek word, "atomos", that means invisible). Each element were subjects of matter and he discovered each one was composed of different kinds of atoms. This idea was never fully developed in this time because Socrates, a great Greek philosopher, never accepted his theory to be true. To conclude, in 450 BCE we found the four elements and now we added on what made up these elements, particles. -
350 BCE
Aristotle's Influence
Coming back to Empedocles 450 BCE prediction, a philosopher named Aristotle greatly believed in the idea of four elements. Even though more studies were being made on the atomic theory, Aristotle's influence kept the "four-element" model accepted for almost 2000 years! -
Period: 500 to
The Metal to Gold Theory
In this time, alchemists spent centuries attempting to make gold from other metals (example: lead). They believed that, with enough experimenting, metal could grow like plants and turn into gold. Even though nobody ever succeeded in ripening gold from a cheap metal they discovered many other things. An invention of chemical symbols for substances (today's elements and compounds) was made along with laboratory tools. For example, beakers and filters that we still use to this day! -
Element's New Definition
At this time, there was a scientist named Robert Boyle who did not believe in the four-element model. With this belief, he put together a new definition for the word element: "I mean by element, simple unmitigated bodies." Also, compared to previous theories, Robert Boyle believed air was a mixture instead of a pure substance. -
New Found Mixtures
During the 1700s, many scientists discovered different substances and how they created mixtures. It wasn't until Antoine Lavoisier experimented with oxygen (with Joseph Priestley's discoveries) that he realized air is a mixture of different elements, including oxygen. Previously people thought air was an element. Also, Henry Cavendish worked with flammable acid (later known as hydrogen) and oxygen, which he discovered produced water. Like air, until then water was thought to be an element. -
Dalton's Theory
In 1808, John Dalton (an English chemist), published a theory on how elements and non-elements are different. This changed the original belief on how all matter was made up of just elements. In his theory, he explained how matter is made up of tiny atoms and each element has its own kind of atom with its own mass. He wrote on how compounds were created when atoms of different elements came together to form molecules. Finally, atoms can't be destroyed. This theory changed everyone's perspective. -
The Impact of Charges
Dalton's theory was a push in the right direction but still did not make a solution for everything in matter. After experimenting with electricity, Michael Faraday found that electric currents could cause chemical changes to some compounds. The atoms inside the compound could gain electric charges and form ions (charged atoms). With this information, he modified the theory explaining how charges could impact or attract within atoms. "Opposite charges attract and as charges repel." -
The Raison-bun Model
A man named J.J Thomson continued on Dalton's and Faraday's work by discovering electrons (a very light negative particle) and what today is known as protons (a heavier positive particle). He wrote on how electrons contain negative charge while the rest of the atom is a sphere of positive charge. Electrons are in this sphere so the atoms are neutral. During this time, H. Nagaoka (Japonese Scientist) modelled the atom like a large postitve sphere with a ring of negative electrons around it. -
The Nuclear Model
In 1911, a worker at McGill University in Montreal named Ernest Rutherford decided he'd test the Raisin-bun model with charged positive particles, smaller than most atoms, called alpha particles. A few of the particles bounced right back from a sheet of gold foil instead of going through. This was very odd and Rutherford made the nuclear model to explain. This model shows how atoms hold something called the nucleus surrounded by mostly empty space but contains fast-moving electrons.
