422-004+E.+O'Reilly+Big+Timeline+Project

**__Ancient Times__**
//(500-450 BC)//
 * 1.~__Leucippus__~**
 * Origin:** Greece


 * Was the first to be certain that there was empty space, which allowed motion to be possible. This empty space was a vacuum and within it atoms existed. The atoms darted about randomly in the void and were invisible. They would combine to form abjects that humans could perceive. Atoms could not be divided because they contain no empty space. He was said to be the teacher of Democritus, but since there is no solid proof of his existence we can't be sure. Most information about him is from writings of Aristotle.

//(460-370 BC)//
 * 2.~ __Democritus__** ~
 * Origin:** Greece


 * Was the first to announce the atomic theory, that the world is made up of atoms and the void in which they move. He believed atom were infinite in number and were not able to be perceived my people because they were so small. He said atoms move around in empty space and will crash into each other creating perceivable abjects. When the atoms separate the object is destroyed. He said atoms are different shapes and sizes. He said atoms were not created and could not be destroyed, so he believed in the conservation of matter.

//(384-322 BC)//
 * 3.~__Aristotle__~**
 * Origin:** Greece


 * Aristotle was highly respected in his time, and since he chose to say the atomic theory was a complete false everyone believed him. He instead believed that the world was made up of continuous matter, there was no void and the matter was not broken up into atoms. Nature was made up of the four elements, fire, water, air and earth and that the possible properties for the elements were dryness, heat, cold, wetness and moisture. Fire contained dryness and heat, water contained moisture and cold, air contained heat and moisture and earth contained dryness and cold.

__1700-1800__
//(1700-1782)//
 * 4.__~Daniel Bernoulli~__**
 * Origin:** Netherlands


 * Bernoulli worked with hydrodynamics as well as the kinetic theory of gases. In his work with fluids he came up with many theories about gases and was one of the first to consider them particles, which led to the idea of atoms and atomic theories. He was also the first to use atoms in his calculations. He used atoms to explain gas pressure was atoms hitting the walls of it's container. His best work is //Hydrodynamique// which was published in 1738. It revolved around the conservation of energy

//(1711-1787)//
 * 5.~__Rudjer Josip Boscowich__**~
 * Origin:** Croatia


 * He was a mathematician and astronomer who found out how to measure the equator of any planet. He is most famous for his atomic theory which is based on Newtonian mechanics and was the base for many following scientists to get theories from, these include Faraday and even Einstein. he made many astrological advances and was also called upon to help secure the Dome of St.Peter's, Rome because of his research of spheres.

//(1743-1794)//
 * 6.~__Antoine Laurent Lavoisier__~**
 * Origin:** France


 * Lavoisier is know as the father of modern chemistry. He tried to be very precise in his measurements and created a very accurate scale to measure mass. Using this scale he proved the law of the conservation of mass and turned people away from the phlogiston way of thinking. He was able to explain the difference between compounds and elements as well as that matter ca be in three stages (solid, liquid and gas). He also learned that when one breathes they inhale Oxygen and exhale carbon dioxide. Lavoisier did extensive work with combustion. He also discovered water was made of Oxygen and hydrogen. He believed in 33 elements, which were to him matter that has not been able to be broken down further.

**__1800-1875__**
//(1766-1844)//
 * 7.~__John Dalton__~**
 * Origin:** England

Dalton had many laws that he came by, the law of partial pressures is one of them. In 1803 he proposed his atomic theory that said all matter was composed of small indivisible particles called atoms, the atoms of the same elements are the same and have unique characteristics making them different from atoms of other elements and that there were three kind of elements, Simple, compound and complex. He was also one of the first to talk about colorblindness. He discovered that all fluids in the same pressure will expand equally with heat. He also created the first periodic table of sort, he wrote down all the atomic weights he measured in his notebook. He theorized a lot on atoms saying they could not be created or destroyed, they only combined in small ratios, all atoms of one element have the same mass and atoms of different elements have different masses. Dalton believed atoms were solid spheres, his first models were made from wooden spheres (pictures above)

//(1776-1856)//
 * 8.~__Amedeo Avogadro__**~
 * Origin:** Italy

Avogadro first began working with electricity and later with atoms. He studied Dalton's work and made the distinction between atoms and molecules. Avogadro's principle was that any gas at the same temperature and pressure contains the same number of molecules. Avogadro's discoveries were mostly ignored until much later, after his death. Contrary to what you might think, Avogadro did not know what a mole was nor did he come up with that number that we call Avogadro's number, that naming did not come about until after his death. The number was created based on Avogadro's principle and that is why it has his name.

//(1870-1942)//
 * 9.~__Jean-Baptiste Perrin__**~
 * Origin:** France

He began his research on cathode rays and X-rays when he was in his twenties. he found cathode rays were negative in charge and studied the affect X-rays had on gases. He is best known for his Brownian movement in which he proved Einstein's theories that colloidal particles behave like gases and he was then able to calculate Avogadro's number. He was able to prove the discontinuity of matter and was awarded a nobel prize for this feat.

__**1875-1900**__
//(1856-1940)//
 * 10.~__JJ Thomson__**~
 * Origin:** Britain

Thomson's greatest contribution to Science was his discovery of the electron on 1897. he also was able to separate some atoms and molecules using positively charged particles which helped lead to the discovery of different isotopes. He is also famous for his model of the atom called the plum pudding model. In this model he thought the atom was a positively charged particle with negatively charged particles randomly placed throughout.

//(1867-1934)//
 * 11.~//Marie Curie//~**
 * Origin:** Poland

One of the first female scientist to hold a high position in society and win a Nobel prize. she discovered Polonium and Radium, two radioactive substances in 1898. She often used radium in a way to help with pain, she believed it had therapeutic properties. She was able to separate a large amount of radium and Polonium from pitchblende. She measured the amount of radioactivity emitted by the substances and invented the word radioactivity. She felt that radioactivity was actually a trait of certain atoms.

//(1845-1923)//
 * 12.~__Wilhelm Roentgen__~**
 * Origin:** Germany

Roentgen is most famous for his discovery of X-rays which he first discovered while experimenting with a crook's Tube and cathode rays in 1895. The tube was covered with a thick black cover so that he could better see the glow that caused the tube to normally glow when being used. across the room his barium platinocyanide coated glass stated to glow. He knew cathode rays were not able to penetrate the glass that the tube was made of, so he knew they could not be the cause of the glowing. He figured a new ray was causing the element to glow, so he called these X-rays as a temporary name. Since they had penetrated his black covering he decided to see what else they could penetrate. When he placed a photographic plate behind the objects, he was able to see if it penetrated them. When he placed his wife's hand in front of them the X rays were able to go through her skin but not her bones. This was the first ever X ray of human bones.

//(1852-1908)//
 * 13.~Henri Becquerel~**
 * Origin:** France

Becquerel's earliest wok involved light and how it was absorbed through crystals. After hearing about Roentgen's X-ray discovery, he wanted to find out if there was any correlation between the glowing of Roentgen's barium platinocyanide from the rays and naturally occurring phosphorescence. He knew Uranium salts, when exposed to light would glow and leave impressions on photographic plates. Henri also knew that these rays were different from X rays because they could be affected by electric and magnetic fields. He then discovered that the salts did not actually need light in order to emit these rays, when in 1896 prior to doing an experiment, he left the salts on photographic plates in a completely dark drawer. This discovery was purely accidental. He was awarded a nobel prize for discovering spontaneous radioactivity.

__1900-1915__
//(1885-1962)//
 * 14.~__Niels Bohr__~**
 * Origin:** Denmark

Bohr was lucky enough to have been taught by both JJ Thomson and Ernest Rutherford. He began to research the structure of atoms and came up with his own model. In his model there were many orbits in which electrons could circle the nucleus. the outer orbit could hold more electrons than the inner orbits. He also theorized that when an electron jumped from and outer orbit to an inner one it emits light. This theory was later turned into Quantum mechanics. When electrons jumped from one orbit to another a different color light was emitted depending on which orbits it moved between.

//(1871-1937)//
 * 15.~Ernest Rutherford~**
 * Origin:** New Zealand

He was at one point the student of JJ Thomson. He began his research with magnetism. he was among the first to identify alpha and beta emissions from radioactive elements. He also discovered a new noble gas element called thoron. he worked with Frederick Soddy to discover that radioactive decay was an atom disintegration. by far his greatest contribution to science was his discovery of the nucleus in 1910. The nucleus was discovered when Rutherford was shooting alpha particles at a thin piece of gold which was then surrounded by photographic paper to see where the particles hit. He expected that all particles would go straight through the gold. To his surprise every once in a while an alpha particle would bounce back off the paper! This proved to him that there must be something in the center of the atom and he reasoned that the protons were not spread throughout but actually centered in the atom because the particles only bounced back 1 in 8000 times. He thought the alpha particles that bounced back had collided with these gathered protons. He was the first to be able to calculate an elements atomic number which it could be identified by and was the first to transform one element into another by shooting alpha particles at it.

//(1868-1953)//
 * 16.~__Robert Millikan__~**
 * Origin:** USA

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