By: Balkaran, Brent & Sanjeet History of the Atom Timeline Physics 30 442 B.C. 1803 1871 1897 1900 1905 1909 1911 1922 1923 1925 1927 1927 1930 1932 Democritus 1939 John Dalton Ludwig

Boltzmann J.J. Thomson Max Planck Albert

Einstein Robert Andrews Millikan Ernest Rutherford Niels Bohr Louis de Broglie Wolfgang

Pauli Werner

Heisenberg Max Born Erwin Schrödinger James

Chadwick Richard Feynman Democritus, along with his mentor Leucippus, were one of the first few people to develop a theory about atoms

Democritus and Leucippus hypothesized much about atomic matter

They hypothesized that everything are composed of atoms, and that they are physically indivisible

They both also hypothesized that atoms are indestructible, are always in motion, and that there are an infinite number of atoms, differing in shape and size

When discussing the mass of atoms, Democritus had said "The more any indivisible exceeds, the heavier it is"

Along with Leucippus and Epicurus, Democritus had first proprosed the earliest views on atoms, and atomic theories, including heavy discussion around the connectivity and shapes of atoms

Democritus mainly postulated the theory of atoms and the void, and was known to be an atomist. He theorized that indivisible atoms and empty void is what the natural world consists of

Democritus is significant in the atomic timeline because he was one of the first atomists to propose the theory that all matter is made up of indivisible atoms John Dalton is well known for his development of the atomic theory

He proposed on the most significant theories for atomic matter during the 1800's

Before his proposition of the atomic theory, he had discovered gas laws, and studied the constitution on mixed gases. All his research with gases led up to his development of the atomic theory

In 1803, Dalton published a table of relative atomic weights, which consisted of 6 elements. With these elements, he hypothesized the structure of compounds, and determined that they can be represented in whole number ratios

The main points in John Dalton's atomic theory are:

1) Atoms are small particles that make up elements

2) Size, mass and other properties are only identical in given atoms. Size, mass and other properties differ in different elements

3) Atoms cannot created, subdivided or destroyed

4) Chemical compounds are formed from when atoms of different elements combine

5) Atoms are rearranged, combined or separated in chemical reactions

Dalton formed this atomic theory by using spherical solid atoms based upon measurable properties of mass. He came to the result that all atoms possess unique characteristics, including weight

He also stated that 3 types of atoms exist: simple, compound and complex

John Dalton is significant in the atomic timeline because he first proposed the atomic theory, and that elements consisted of atoms Joseph John Thomson is well known for his discovery of the electron

Many scientists had believed that atoms were built up from a more fundamental unit, and believed that this unit would be equivalent to the size of the smallest atom, which is hydrogen

J.J. Thomson made the discovery of what is now known as electrons. In 1897, he suggested that the fundamental unit was over 1000 times smaller than an atom, including hydrogen

The exploration and the properties of cathode rays is how Thomson discovered subatomic particles, more specifically, electrons

His experiments with cathode ray tubes are very significant, in how he used cathode ray tubes to experimentally determine the charge to mass ratio of an electron

Thomson is also very well known for his development of the plum-pudding model of the atom

Joseph John Thomson is significant on the atomic timeline in how he had discovered the electron, determined the charge to mass ratio of an electron, and developed an atomic model, called the plum-pudding model Ludwig Boltzmann is most noted for his development of statistical mechanics

Statistical mechanics is also known as statistical thermodynamics, and uses the probability theory to study the thermodynamics of particles, usually a large number of particles

Mass, charge, structure, and other properties of atoms, are used to determine the visible properties of matter. To determine this, statistical mechanics is used

Ludwig Boltzmann is significant in the atomic timeline in how his development of statistical mechanics predicts and explains the properties of atoms and matter Many contributions to theoretical physics have been made by Max Planck

Planck's fame is most noted by his role of the originator of the quantum theory

He was the first scientist to make contributions to the quantum theory. This theory helped the atomic and subatomic processes make more sense to humans.

The discrete units of energy are quanta, and used quantization for his atomic experiments

On December 14, 1900 Planck proposed that electromagnetic energy could only be released in quantized form. This propose was named Planck postulate. This theory formed the formula E=hv, which says that energy can only be a multiple of an elementary unit

His experiment, that consisted of a hot, glowing object that emitted light, proposed the idea that quantization was used

Through this experiment, Planck determined that radiation is quantized Albert Einstein created the general theory of relativity, which had a major effect on physics for a long period of time

In 1921, he received the Nobel Prize in physics for his mass-energy equivalence formula (E=mc2), and for creating the photoelectric effect. This was very helpful in creating the quantum theory

In 1916, Einstein made a paper about how the theory of relativity could be expanded to gravitational fields

In 1911, based on a new theory of general relativity, he calculated that light from one star would bend by the sun’s gravity

Einstein proposed the quantum of light

He stated that although light behaves like a particle, it has a wave like nature, giving it a dual nature property

The theory of special relativity was used to state the equivalence of energy and mass

Albert Einstein is significant in the atomic timeline, along with many other scientific aspects, in how he proposed the quantum of light

Einstein’s theory of relativity changed the atomic model in a way that he created a completely new formula that is the most famous formula, any scientist has created

Einstein helped start the quantum theory through his discovery of the photoelectric effect. In 1917 he applied the general theory of relativity to the universe as a whole Robert Andrews Millikan is an American experimental physicist, most notably known for his work on the photoelectric effect

Millikan is also notably famous for his efforts on the electron. He determined the charge and mass of an electron

Although the charge to mass ratio of the electron was discovered by J.J. Thomson, Millikan's famous oil drop experiment/method had led to the discovery of the actual charge and mass values of an electron

The charge and mass values of an electron is fundamental for atomic theories, which is why Robert A. Millikan is significant on the atomic timeline Ernest Rutherford is known to be the "father of nuclear physics" and is considered to be one of the greatest experimental scientists

Rutherford is known for his demonstration of the nuclear nature of atoms

In 1911, Rutherford formulated the Rutherford model of the atom. In this model, there is a very small charged nucleus present. In this nucleus, there is much of the atom's mass. This nucleus is also being orbited by low-mass electrons

Rutherford had executed an experiment called the gold-foil experiment

In this experiment, Rutherford used alpha particles as atomic bullets, and he probed the atoms in a piece of very thin gold foil. Rutherford had discovered that the nucleus was very small, it was positively charged and that it was very dense

Ernest Rutherford is significant in the atomic timeline in how he had established properties of the nucleus through his gold foil experiment, had discovered alpha, beta and gamma rays in radiation, and also developed the Rutherford model of the atom Niels Bohr is very notable for his work in the contributions to understanding quantum mechanics and the atomic structure

Bohr is known for his work in making the Bohr atomic model in 1913, where it is similar to a planetary model. This model depicts the whole atom as a small, positively charged nucleus, that is present in the middle of the model. Around the nucleus, it is orbited by electrons that travel in a circular motion, similar to the solar system

Bohr also believed that, only in discrete steps (not continuously), electrons move from one energy level to another

Bohr had proposed an atomic structure theory which stated that the outer orbit of an atom could hold more electrons than the inner orbit of an atom. He also stated that atoms absorb or emit radiation only when the electrons jump between states

Niels Bohr is very significant in the atomic timeline in how he had developed the Bohr atomic model, which we still use today, and had provided a much more improved understanding of the atomic structure Louis de Broglie had many theories, including one critical one, called the matter and wave-particle duality theory

This theory set the basis of wave mechanics

Another critical theory of Broglie's was the duality of the laws of nature

Both of these theories were supported by Einstein, and confirmed and generalized by other scientists. Broglie had discovered that electrons had a dual nature, which is similar to both waves and particles (particle/wave duality) Although he worked primarily in the field of quantum mechanics, Wolfgang Pauli had made many important and significant scientific contributions

In 1924, Pauli proposed a new quantum degree, also known as quantum number

In 1925, Wolfgang Pauli states the quantum exclusion principle for fermions

In 1926, Pauli used the matrix theory of quantum mechanics to derive the hydrogen atom

Pauli had also made another major contribution in 1931. In order to explain the apparent violation of energy conservation in beta decay, he had put forth the neutrino hypothesis Werner Heisenberg is notably well known for being awarded the Nobel Prize in Physics in 1932 "for the creation of quantum mechanics"

Heisenberg had proposed the uncertainty principle, which is also known as the principle of indeterminacy

This principle showed that knowing both the position and momentum (or velocity) of a particle at the same time is uncertain. In other words, you are not able to determine both the position or momentum of a particle simultaneously

Heisenberg had also described atoms by means of formulas, that were connected to the frequencies of spectral lines

Werner Heisenberg is significant in the atomic timeline in how he proposed the uncertainty principle, and was the originator of quantum mechanics Max Born had made many contributions to science, including the development of quantum mechanics, solid-state physics and optics

In 1927, Max Born interprets the probabilistic nature of wavefunctions

Born made the proposition that atoms act like waves, an have movements similar to waves

In the same year, Max Born, along with Robert Oppenheimer, introduce the Born-Oppenheimer approximation Erwin Schrodinger is well known for his development of a wide number of fundamental results in the quantum theory field

These fundamental results that Schrodinger developed, led to form the basis of wave mechanics

He had formulated the wave equation, which is also known as the Schrodinger equation, and the formalism and matrix mechanics were revealed

At an atomic point of view, the wave mechanics that Schrodinger developed, described the behavior of quantum systems for bosons. Wave mechanics was also introduced as a mathematical model of the atom

He had also viewed electrons as continuous clouds

Erwin's wave equation described the form of the probability that waves had. It was used to govern the motion of small particles, and how these waves are affected or altered by external forces James Chadwick is notably well known for his famous discovery of the neutron

In 1932, Chadwick was conducting an experiment in which alpha particles were used in, and discovered an atomic particle that was lacking an electric charge

Chadwick then discovered that the mass of this neutral atomic particle had a mass that was close to a proton

James Chadwick is very significant in the atomic timeline in how discovering the neutron was a major discovery Richard Feynman is well known for his work in quantum mechanics, theory of quantum electrodynamics, and as well as particle physics

Feynman had contributed much to atomic theories

In 1939, he found the Hellmann-Feynman theorem, along with Hans Hellmann

In 1947, quantum electrodynamics is presented to Feynman

In 1957, a vector/axial vector (VA) Lagrangian is proposed by Richard Feynman, along with other colleagues such as Murray Gell-Mann, Robert Marshak and E.C.G. Sudarshan

His major contribution towards the atomic timeline is his development of the Feynman diagram, which show mathematical expressions governing the behavior of subatomic particles

With his Feynman diagrams, Richard had determined that an electron + a positron will create a photon REFERENCES: http://en.wikipedia.org/wiki/Democritus

http://en.wikipedia.org/wiki/John_Dalton

http://en.wikipedia.org/wiki/Ludwig_Boltzmann

http://en.wikipedia.org/wiki/J._J._Thomson

http://en.wikipedia.org/wiki/Max_Planck

http://en.wikipedia.org/wiki/Albert_Einstein

http://en.wikipedia.org/wiki/Robert_Andrews_Millikan

http://en.wikipedia.org/wiki/Ernest_Rutherford

http://en.wikipedia.org/wiki/Niels_Bohr

http://en.wikipedia.org/wiki/Louis_de_Broglie

http://en.wikipedia.org/wiki/Wolfgang_Pauli

http://en.wikipedia.org/wiki/Werner_Heisenberg

http://en.wikipedia.org/wiki/Max_Born

http://en.wikipedia.org/wiki/Erwin_Schr%C3%B6dinger

http://en.wikipedia.org/wiki/James_Chadwick

http://en.wikipedia.org/wiki/Richard_Feynman

http://atomictimeline.net/index.php

http://www.barcodesinc.com/articles/timeline-on-atomic-structure.htm

http://craigjm.tripod.com/physics.html

http://hi.fi.tripod.com/timeline/

http://en.wikipedia.org/wiki/Timeline_of_atomic_and_subatomic_physics

http://en.wikipedia.org/wiki/Atom

http://education.jlab.org/atomtour/

http://www.history-timelines.org.uk/events-timelines/23-atomic-timeline.htm

http://www.atomicarchive.com/Bios/Born.shtml

http://www.nndb.com/people/348/000179808/

http://www.nobeliefs.com/atom.htm

http://profmokeur.ca/chemistry/history_of_the_atom.htm

http://web2.uwindsor.ca/courses/physics/high_schools/2005/Brownian_motion/History.html

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