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Atomic History Attempt #3
Transcript of Atomic History Attempt #3
Proposed his model of the atom in 1915
Won the Nobel Prize in 1922 Worked in England with J.J Thompson and Ernest Rutherford in 1912. Planetary Model Electrons orbit the nucleus in orbits that have a set size and energy. The energy in an atom is quantized...
Only certain orbits with certain radii exist (there are no orbits in between). The size of the orbit correlates to the energy of the orbit (e.g. smaller orbit=lower energy). Radiation is absorbed and emitted when electrons move from one energy level to another. How did he solve the problems with Rutherford's model? The answer came from Planck's constant, which explained the stability of atoms. Bohr discovered that the ratio of energy in electrons to the frequency of their orbit was equal to this constant (the proportion of light's energy to its frequency). From this, he concluded that electrons jump in between energy levels without ever existing in an in-between state. By absorbing a photon an electron can jump up a level. By emitting a photon an electron can jump down a level. The wavelength of the absorbed/emitted light is such that the photon will carry the energy difference between the two energy levels. Ground State 1st Excited State 2nd Excited State Ionization Potential Bohr's model predicted patterns in the spectral series (light emissions) of hydrogen atoms. Past this point the electron is no longer bound to the atom and the energy levels form a continuum. Bohr's model paved the way for quantum mechanics. However, it is somewhat oversimplified and has multiple flaws Is based on experimental work with only simple atoms. Violates the Heisenberg Uncertainty Principle as it considers electrons to have both a known orbit and radius. Does not predict the relative intensities of spectral lines. New Zealand Chemist & Physicist
Won the Nobel Prize in 1908 and knighted in 1914
Carried out his experiment in 1909 Believed in Lord Kelvin's Plum Pudding Model Designed original experiments with high-frequency, alternating currents. Wanted to see how big an atom was.
Used radioactivity Won the Nobel Prize in Chemistry
Known for his Gold Foil Experiment in 1911 His hypothesis was incorrect The Actual Result What He Expected Realized that atoms have a dense central core, explaining why the alpha particles deflected. Positive charges were thought to be spread out evenly.. These findings helped him with the discovery of the proton! Although Rutherford's findings laid the foundation for modern nuclear physics, there were some inconsistencies with his proposed model. He proposed that orbiting electrons have centripetal acceleration that loses energy through electromagnetic radiation. Rutherford implied that the atom should be not be stable, which was later proven wrong by Bohr. Joseph John "J.J." Thomson Born on December 18, 1856 in Manchester, England
Was a British physicist who discovered the electron
Awarded the Nobel Prize in Physics in 1906, and the Knighthood in 1908 Democritus Democritus was born in 460 BC, and was one of the two founders of ancient atomistic theory. Father of the modern science Democritus' atomic theory "A-tomos"--- undividable
Always in motion
Infinite numbers of atoms
They are solid, homogeneous, and indestructible
The size of the atom is not specific but can be different depending on the various factors influencing them
The strength of an object depends on the shape of the atoms the objects has
Matters are changed of group atoms not from changes in the atoms
Due to size, shape and movement of the atoms, there are different properties of matter. In 1897, Thomson was experimenting with a vacuum cathode-ray tube to study the nature of electric discharge in the tube, during which he discovered the electron. No experiments http://plato.stanford.edu/entries/democritus/http://www.thebigview.com/greeks/democritus.html Other important scientists •Robert Andrews Millikan
•Louis de Broglie
•Werner Heisenberg Robert Andrews Millikan Robert Millikan, 1909 he performed an experiment called “Oil Drop experiment” to determined the size of the charge on an electron. For years, scientists had known that if an electric current was passed through a vacuum tube, a stream of glowing material could be seen; however, no one could explain why. This apparatus consisted of a vacuum glass tube, with two metal disks positioned at opposite ends that were connected to a voltage source. sprayed a fine mist of oil droplets into the chamber Define the terminal velocity By placing two electrically-charged metal plates - one positive and one negative - on either side of the tube, Thomson observed that the glowing stream got deflected towards the positive plate, indicating that the stream was negatively-charged. To send X-ray to apply an charge Apply an electric voltage E: electric field
m: mass of the oil drop
q: charge of the electron The charge was always a multiple of -1.6 x 10 -19 C, the charge on a single electron. http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/ryan_mcallister/Slide3.htm Louis de Broglie He speculation when electrons were found to diffract and interfere very much as light does, since light can behave as a particle, particles are able to behave as waves as well. p = mv = h /λ
where v = speed of particle , λ = wavelength
λ = h / mv DeBroglie's speculation was taken up in 1925 by Erwin Schrodinger who fully developed the whole thing into QUANTUM MECHANICS. Werner Heisenberg http://www.launc.tased.edu.au/online/sciences/physics/debroglie.htmlx Uncertainty Principle States that locating a particle in a small region of space makes the momentum of the particle uncertain; and conversely, that measuring the momentum of a particle precisely makes the position uncertain. Heisenberg’s uncertainty principle is one of the most celebrated results of quantum mechanics and this principle is mathematically manifested as non-commuting operators. The more precisely the position is known that more uncertain the momentum is and vice versa. To measure the position of an electron there must be a collison between the electron and another particle such as a photon. Equations:
To assume the particle position
Uncertainty in the momentum of the particle; using Eq
To combine two equations together, we get
More refined treatment later Thomson theorized that this stream was in fact made up of small particles, pieces of atoms that were negatively-charged. These particles were later named 'electrons'. Thomson with his experimental equipment. Ernest Rutherford John Dalton - Born in 1766, in England
- Major Contribution to Atomic theory in 1803
- He was a teacher, but also a Chemist, Meteorologist, and Physicist
- Recorded the weather everyday for 57 years
- Credited with the discovery of colorblindness, a condition which he himself suffered from
- Died in 1844, in England All matter is made up of atoms. Atoms cannot be divided and cannot be destroyed All atoms of specific elements have the same mass and properties Compounds are created through two or more types of atoms combining A reaction is the rearrangement of atoms, not the creation of new ones one of two or more atoms with the same atomic number but with different numbers of neutrons Isotopes Erwin Schrödinger - Born 1887, in Vienna, Austria
- His profession in life was Physics
- He also took interest in philosophy, and theoretical biology
- Died 1961, in Vienna, Austria Quantum Mechanical Model of the Atom Schrödinger's Equation While experimenting, Thomson measured the charge-to-mass ratio (e/m) of the electrons. While experimenting, Thomson measured the charge-to-mass ratio (e/m) of the electrons. In another experiment, he measured the charge-to-mass ratio of positively-charged H+ ions, and found that it was about 2000 times smaller than that of the electrons. From Michael Faraday's earlier studies of electrolysis, it seemed plausible to assume that the magnitudes of charged of the electrons and the hydrogen ions were the same. Therefore, Thomson concluded that the electron was about 2000 times smaller than the hydrogen atom. electron hydrogen atom mass of electron = 1/2000th mass of hydrogen atom 2000 1 Since the electrons were so small, he suggested that they could have only come from inside atoms. So, John Dalton's idea that the atom was indestructible or indivisible had to be revised.... In 1904, Thomson proposed his own Atomic Model, which suggested that the atom was a sphere of positive matter in which negatively-charged electrons were positioned by electrostatic forces. It was known at that time that atoms were electrically neutral, so Thomson imagined that the electrons must be embedded in a sphere of positive charge, and hence the charges must balance out. Thomson's atomic model is also known as the "Plum Pudding Model", since the electrons in his atom resemble the bits of plum in a plum pudding. Problems with Thomson's Atomic Model He could not explain the presence of the atomic nucleus within the atom.
He could not explain why atoms react with one another. Although Thomson's atomic model possessed these flaws, his contributions have been highly significant towards the development of the Modern Atomic Theory. It was these shortcomings of Thomson's model that inspired Ernest Rutherford (1871-1937) to do further research on the structure of the atom, and propose his own Atomic Model (the Rutherford Atomic Model). By: Elena, Alex, Shantanu, Lachlan, and Ishan
For: Ms. Ameen
Date September 17, 2012 Atomic History! Thank You!