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500 BCE
Leucippus and Democritus have an idea
Around 2,500 years ago, Ancient Greece was known for its intellectual and philosophical genius. These two definitely live up to that reputation. These two were most likely the first to conceive the idea that all matter is composed of tiny particles. Their philosophy wasn't very complex, though; they simply believed that at some point you would be unable to break an object down any more. They called these particles "a tomos", meaning "uncuttable." -
384 BCE
Aristotle disagrees
Aristotle disagreed with Leucippus and Democritus. He disagreed that matter was made up of tiny particles. He believed that there were four fundamental elements; air, earth, fire, and water. This led to nearly 2000 years of "science", based on this flawed idea. -
322 BCE
The beginning of Alchemy
In 322 BC, Alexander the Great conquered Egypt. During this time of philosophical discovery, Greek philosophers became interested in the religion of the Egyptians. It just so happens that the idea of the four elements of nature, held by the Greeks, aligned with the Egyptian religion. This resulted in the word Khemia (the Greek word for Egypt), which eventually resulted in the word Alchemy. -
600
The spread of Alchemy
Arabs accupied Egypt and further developed Alchemy. They eventually spread it to the west. In this time they had figured out some things; Metals are made up of mercury and sulfur in varying proportions. They also figured out that Gold is the perfect metal, all others being "Baser" metals which are capable of being transmuted into gold using a substance known as a Philosophers Stone. Alchemists used this concept to the human condition, seeking spiritual purification/immortality -
1500
Divison of the Alchemists
As time went on, alchemists in Europe separated into two groups. In the west, alchemists wanted to discover new compounds, reactions, and chemical processes (this eventually would lead to chemistry). These alchemists invented processes like distillation, percolation, extraction, and rudimentary chromatography. The other group stayed with the traditional form of alchemy, continuing to search for immortality and the transmutation of base metals to gold. -
Vitalism
Vitalism was the belief that living organisms are fundamentally different from non-living entities because living organisms contain a "vital spirit." This meant that living things are governed by different principles than non-living things. -
The Phlogiston Theory
This idea was first proposed by Johann Joachim Becher. This proposed the existence of a fire-like element called "phlogiston", which was contained within combustable things and released during combustion. Therefore, if a substance burned it was because it contained Phlogiston. Carbon dioxide was called "dephlogisticated air" as it was no longer capable of burning. -
Anotine's proposition
French chemist Antoine Lavoisier was a different from most before him, as he relied on quantitive observation to develop conclusions. He would eventually dispelled the Phlogiston Theory by proving that oxygen causes combustion, not phlogiston. He came up with the law of conservation of mass. This states that even if matter changes shape or form, its mass stays the same. This was groundbreaking, and set the stage for future discoveries about chemistry. He was later, sadly, beheaded. -
Benjamin Franklin
Everyone knows the story of Benjamin Franklin and electricity, but it had a bigger impact than many think. He discovered that there are positive and negative electrical charges; like charges repel, opposite charges attract. -
Joseph Lous Proust's law
Joseph Lous Proust would discover the Law of Definite Proportions, also referred to as the Law of Constant Composition. This states that a chemical compound always contains exactly the same proportion of elements by mass. -
John Daltons atomic theory (continued)
His theory also states that different atoms of different elements combine in simple whole numbers to form compounds. Lastly, it states taht Atoms cannot be crated or destroyed; when a compound decomposes, the atoms are recovered unchanged. -
John Daltons atomic theory
James Dalton was also a great mind for chemistry in the 1700's, with his contributions to atomic theory. He discovered that elements existed as packets of matter. Daltons Atomic Theory of Matter states the following. Matter is made up of atoms that are indivisible and indestructible. All atoms of an element are identical (later discovered to be untrue). Atoms of different elements have different weights and different chemical properties. -
Scientists wonder; why?
Scientists began using discharge tubes to try to figure out exactly what things were made of. Because of the way the device emitted the ray the scientists used, the figured out that there was a positive and negative charge present. This strange phenomenon would lead to much more important discovery. -
Joesph John Thompson investigates
After the discovery of this, J.J. Thompson investigated further into the behavior of these rays. Through extensive experimentation, he was able to estimate the mass of the rays. Strangely, the mass was around 1000 times smaller than the mass of hydrogen, the smallest matter known at the time. He concluded that these "rays" were actually very small, light, negatively charged particles (which he called corpuscles). These particles were what we know today as electrons. -
Becquerel
Henri Becquerel discovered radioactivity in Uranium ore. -
Curies (Marie and Pierre)
These people discovered and isolated polonium and radium from uranium ores. The study of radioactivity gave scientists at the time the idea that there had to be something inside the atom that gave it its identity, and that if that thing were to be changed, the atom would change/transmute into another element. -
Earnest Ruthford
Earnest Ruthford created an experiment using a thin sheet of gold foil and a screen coated with zinc sulfide. He projected alpha particles at the foil and, to his surprise, they didn't all go straight through; some projected off. With this information, he concluded that the positive charge of the atom must be concentrated in a small area. He called this area the nucleus. But because most of the particles went through, he also concluded that most of the atom was made up of empty space. -
Millikan
Millkian was the person who calculated the mass and charge of an electron. -
Niels Bohr's model
Using Ruthford's experiment, Bohr was able to predict the most likely positions of electrons within the atom. The result was the planetary model, widely known even today. This presents the electrons in orbit of one central nucleus. His model was later discovered to be flawed, but it is still in many ways very close to reality. -
The birth of Quantum Theory
German physicist Werner Karl Heisenberg discovered that it is impossible to know the momentum or the exact position of any subatomic particle. This basically destroyed the possibility of the planetary model being true to life. So Heisenberg, along with many other physicists, proposed a new idea; Quantum Theory. -
The birth of Quantum Theory (continued)
This theory proposes that electrons are not particles or waves, but instead were sort of both. With this taken into account the location of an electron can only be stated in terms of probability; they are more likely to be found in some areas than others. These regions are called orbitals. This theory is currently the modern understanding of atoms. The current model of an atom looks much like a cloud, with colored areas representing areas of higher or lower likelihood of having electrons. -
James Chadwick
James Chadwick proved the existence of another subatomic particle which had no charge. He called this particle the neutron.
