-
Jan 2, 1000
Aristotle
Around 400 BC: When the idea of the atom was first proposed by Democitius around 400 BC, Aristotle did not like the idea. He claimed that there was no smallest part of matter, and that substances were simply made up of differnet proportions of the things he believed all other things were made up of: fire, air, earth, and water. Because there were no experimental grounds with which to test the atom theory, Aristotle prevailed among the people mainly because his philosophy was better. -
Antoine Lavoisier
He is known as the father of modern chemistry. He discovered that water is made up of 2 parts hydrogen, 1 part oxygen. Biggest of all, he created the analytical balance that states matter/atoms are never created of destroyed, they solely change forms. This gave us the most fundemental principle of physics: the law of conservation of mass. -
John Dalton
John Dalton came up with the Atomic Theory. It stated that all matter consists of many tiny particles, these are indestructible and unchangable, the elements are characterized by the mass of their atoms, and that when elements react, their atoms combine in whole number ratios. He was the first person to make a system of atomic weights, which would become what we know today as the Periodic Table. However, his theory lacked what the smaller were, so that paved the way for later research. -
JJ Thomson
JJ Thompson made a enormous step forward in science when he discovered the electron. He used a cathode ray tube in his experiments to come to an understanding why an electric current could be seen within it. When he introduced an electrical charge the glow would bend towards the positive side. Thus concluding that inside atoms were negative charges. He also came up with the Plum Pudding model: all postive and negatively charged parts are all inside one central space. -
Henri Becquerel
When Becquerel began studying chemistry, the year was 1896, and the X-ray had just been invented. He wanted to see if there was a connection between X-rays and naturally occuring phospherence. From his father he obtained uranium salts. He studied them with photographic plates and realized they bacame fogged. Later, it was identified that uranium emitted rays of radiation. He won the Nobel Prize in 1903 for his discovery of natural radiotion. -
Marie & Pierre Curie
These two people are credited with discovering polonium and radium. The discovery of radiation by Becquerel inspired them to make their own anaylses, and so they began to study the thereaputic properties (mainly) of those two things. They were used to illeviate suffering during WWI, by using its radioactive porperties to "kill off" diseases. They were the first to discover that this could be done, and they won the Nobel Prize in 1903, along with Becquerel. -
Max Planck
At a time when traditional physics were forgotten, Planck made a new assumption: energy, instead of being continuous, comes in distinct "packages." These were called quanta. He found that energy that is radiated is directly proportional to its wavelength. Using his findings, he determined that a quantized molecule could only take on certain values. It, once again, had to be proportional the frequency of vibration. This was Planck's constant. 6.626068 × 10^-34 m^2 kg / s. -
Henry Mosely
Mosely studied under Rutheford. He was a British chemist who developed X-rays in order to study atomic structure. This lead to a more accurate placement of elements in the periodic table, with closer calculation of atomic number. He demonstrated that they were not arbitrary, but that they had a physical basis and could be meausred. This leads to how we understand chemistry, and science, today. -
Robert Millikan
He was the first person to find the mass of an independent electron. He was able to do this with the oil drop experiment. All Millikan did was put a charge in a drop of oil (first measuring it's mass) and then measuring the force gravity had on it. He let them fall in the apparatus until they reached terminal velocity. Then, the chamber was illuminated with X-rays, and the air ionized, causing electrons to "stick" to it. After some math it was determined 1 electron weighed 1.5924(17)×10^-19C. -
Niels Bohr
Bohr is credited with creating the planetary model of an atom. He was to solidify the wrok of Rutheford, whose model was theoretically unstable. This was because unlike planets and the sun, electrons were charged and could orbit in any direction, including the possiblilty of destroying the nucleus. Bohr then assumed their orbits were stationary, and came up with the formula 2n^2 to tell how many electrons each orbit could hold. Higher energy orbitals were further away from the nucleus. -
Ernest Rutheford
Taught by Thomson, Rutheford's model had all positively charged particles in the tiny dense center of the atom: the nucleus. Also, since protons and elctrons are oppositlely charged, they won't be pulled towards eachother so the nucleus could not be destroyed. They said that the nucleus is 10000x smaller than the atom itself, but makes up nearly all of the wieght. This is radical thinking, but it is closest to the thinking we have adopted today. He also went on to teach many other physicists. -
Erwin Schrodinger
He is credited with finding electron arrangement. He siad that electrons behave in a wave like pattern, rather than just particles at their exact location, uncalculable. Schrodinger's view of the atom is often thought about like layers on layers. There are electron shells that circle the nucleus. Each shell has an identical number of subshells. Those are furhter divided into orbitals, which are one distinct region, and can hold two elctrons max. This is necessary for chemical bonding. -
Werner Heisenberg
Heisenberg is recognized with discovering the uncertainty principle. It was a key discovery for quantum theory. He defined it as "The uncertain relation between the position and the momentum of a subatomic particle." This relation has profound implications for simple things such as "causality and determination" of the future behavior of that particle. This means we can never really know position and momentum at once. -
James Chadwick
Taught by Rutheford, he made a vital contribution to the world of science: he proved the existence of neutrons in atoms. Elementary particles with no electric charge. In contrast with the helium nuclei, which are charged, and therefore repelled by electrical forces present in the nuclei of heavy atoms, this new atomic peice didn't need to overcome any electric barrier and is capable of penetrating and splitting the nuclei of even the heaviest elements. He was awarded the Nobel Prize in 1935. -
Democritus
Around 400 BC: He came up with the first model of the atom. Democritus theorized that there was a simple part in every substance that was irreducable and indestructable. Since he knew all things on Earth were stable, there had to be something that was the smnallest. Think: how many times can you cut one thing in half? He believed that everything in the universe was composed of atoms, the atoms were dense and completely solid, and the atoms differed in their size, shape, and weight.
