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Aristotle and Democritus
Aristotle and Democritus were greek philosiphers.Aristotle lived from 384-322 BC, and Democritus lived from 460-370 BC. Aristotle thought that matter could be divided infinately. Democritus, however disagreed; he thought that matter could be divided, but only to the smallest particle of matter. He called this particle the atom. -
Lavoisier - Law of Conservation of Mass
Lavoisier was a French chemist who was born in 1743. He died in 1794; he was decapatated during the French Revolution.
At the time, chemists thought that when a metal was heated it became on oxide, which had a greater mass than the original metal. Lavoisier disproved this; he heated mercury in a confined volume of air, and proved that no mass was lost or gained. This is the Law of Conservation of Mass: matter never gains or loses mass when it undergoes a change. -
Dalton - Atomic Theory
Dalton was born in 1766 and lived until 1844.
Dalton is well known for his Atomic Theory. His thoery disproved Aristotle, and agreed with Democritus's view on atoms.
Dalton's Atomic Theory states:
All matter is composed of atoms, which are indivisible and indestructable. All atoms of an element are identical, and atoms of different elements differ in size and mass. Compounds are created from atoms, and chemical reactions rearrange the structure of the reacting atoms. -
Dalton (Continued)- Spherical Model
Dalton beleived that the atom was one spherical particle that had no chare and that could not be broken up into any smaller componants. Based on this theory, Dalton created the Spherical model of the atom. -
Proust - Law of Definite Proportions
Joseph Proust was a French Chemist. He was born on Spetember 26, 1754. He died on July 5, 1826. He is well known for the Law of Definite Proportions. After conducting many experiments during the very late 1700s and very early 1800s, he proved this law. The Law of Definite Proportions states that a chemical compund contains the same proportion of elements by mass. For example, pure water is 8/9 oxygen and 1/9 hydrogen. -
JJ Thomson - Discovery of the Electron
JJ Thomsn lived from 1856 to 1940.
He is well known for his Cathode Ray Tube experiment. Using a cathode ray and a magnet, Thomson discovered the beam it produced is made of negatively charged material. Through other experiments, he also discovered that the mass of these negative prticles is approximately 2000 times smaller than a hydrogen atom. Because of this, he thought that these particles must come from inside the atom, disproving Dalton's theory that atoms cannot be broken up. -
JJ Thomson (continued) - Plum Pudding Model
After discovering electrons with his Cathode Ray Tube experiment, Thomson theorized that if electrons are negatively charged particles, then there must be a positive element to the atom as well. So, he made the Plum Pudding Model. The Plum Pudding model has a number of negatively charged electrons contained in a pudding-like, positively charged ball. -
Rutherford - Gold Foil Experient
Ernest Rutherford was born in New Zealand on August 30, 1871. He died on October 19, 1937. He is known for his Gold Foil experimet. He, with help from his assistant Hans Geiger, shot alpha particles through a sheet of gold foil. They thought the particles would go through the foil, but sometimes the particles bounced back. Rutherford found that the alpha particles must be hitting something small, dense, and positively charged; the nucleus. -
Rutherford (continued) - Nuclear Model
Once Rutherford discovered the nucleus, he created a new model of the atom. In this model, the nucleus is small, dense, and positively charged. Around the nucleus is a lot of empty space, where negatively charged electrons travel around the nucleus. -
Soddy - Isotopes.
Frederick Soddy was born in 1877, and died in 1956. He won the Nobel prize for physics in 1921, and worked with Rutherford on the concept of radioactive decay in the early 1900s. He also created the theory that there are isotpes-some elements are exactly the same, but have a slightly different mass due to nuetral particles. This was a controversial theory until Chadwick discovered and proved the existence of neutrons. Soddy turned to economics and quit science after winning the Nobel Prize. -
Bohr - Bohr Model
The Bohr model of the atom is based off the following:
-electrons are in different orbits (or shells) with different energy levels
-electrons can have one energy level or another, but not anything in between.
-by gaining/losing energy, an electron can move to a different orbit
- the closer to the nucleus an orbit is, the lower its energy level. The farther from the nucleus, the higher its energy level -
Discovery of the Proton
It is hard to say who discovered the Proton - once it was discovered that there were negatively charged electrons in an atom, scientists knew there had to be something positively charged to balance out the negative charge. When Rutherford discovered the nucleus, he discovered it was positively charged, proving that is where the protons of an atom are. The term proton seems to be created by Rutherford, but the idea of positively charged particles was around since electrons were discovered. -
Heisenberg's Uncertancy Principle
Heisenberg was a German Chemist who was born in 1901, and died in 1976. He created the Uncertancy Principle. The Uncertancy Principle states that we cannot accurately predict the movement of electrons; however, it is possible to calculate how likely it is to find an electron in a certain place in an atom. It also states that the more accurately you calculate the position of an electron, the less accurately you will be able to calculate the momentum, and vice versa. -
Wolfgang Pauli - Pauli's Exclusion Principle
Pauli was an Austrain Psysicist who was born in 1900. He dies of Pancreatic cancer in 1958. In 1945, he won the Nobel Prize for Physics. He created the Exclusion Principle. This Principle states that in an atom, no two atoms can have the same quantum numbers. Quantum numbers explain the identity of an electron, such as its energy level and the distance from the nuetron that its orbit is. -
Schrodinger - Electron Cloud Model
Schrodinger was an Austrian physicist; he was born in 1887, and died in 1961 of tuberculosis. He won the Nobel Prize for physics in 1933. Schrodinger built upon the ideas of Bohr, and created a probability function to find the probability of an electron being in a certain spot in an atom. From this, and building off the ideas of other scientists, he created the electron cloud model, which shows the probablity of an electron's location in an atom. -
Chadwick - Discovery of the Neutron
James Chadwick was born in 1891. He was awarded the Nobel Prize in Physics for discovering the neutron. Before this discovery, scientists did not understand why the mass of an atom was more than the atomic number. Rutherford throught there might be a particle that was neutral but had a mass similar to a proton-he called this a neutron. Chadwick did experiments-he bombarded beryllium with alpha particles; this removed a neutron from the atom, and proved the existance of neutrons. He died in 1974. -
Modified Nuclear Model - Chadwick and Rutherford
The Modified Nuclear Model combined Rutherford's Nuclear Model with Chadwicks discovery of the neutron. In this new model, both neutrons and protons are depicted in the nucleus, with electrons orbiting around the nucleus. -
Bohr - Quantum Theory
Niels Bohr was born in 1885. He received the Nobel Prize in Physics in 1922, and died in 1962. He created a theory called Quantum theory. This theory was created because electrons were a mystery-they acted like both particles and waves. It states that electrons can be viewed in two ways: as a particle or as a wave, but not both at the same time. The theory also states that the results of an experiment are deeply affected by the measurement tools used in the experiement.
