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------------ 2754 - PERIODIC TABLE - why is gold yellow?
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- The Periodic Table of Elements has changed from atomic weights to “atomic numbers“, which is the number of protons in the nucleus. For a neutral atom of an element there are an equal number of electrons as protons.
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- Simple enough! But the table has seen constant revisions. Now we are up to the element 117, with 117 protons. There are some 92 natural elements. Uranium being one of the heaviest. These heavy elements are radioactive and decay into lighter elements. The heaviest elements are created in particle accelerators for physicists to study.
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- Because the electron orbitals for these heavier elements gets so large and complex the elements behavior begins to differ from what is expected. The chemical behavior of each element should depend on its valence electrons, those in the outermost orbital.
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- However, these electrons, in order to remain in orbit , are achieving velocities near that of light. Relativistic equations begin to become part of the mix.
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- The more protons in the nucleus the greater the atomic number, and the greater the positive charge. For a neutral atom the same number of electrons are orbiting the nucleus as protons in the nucleus. The outer most orbital electrons, the “valence” orbitals, govern the chemical properties of the element.
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- For heavier elements the outermost electrons begin to carry enough electrostatic negative charge to neutralize some of the attraction of the positive charge of the nucleus.
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- As the nuclear charge increases with more protons the speed of electrons in the inner orbital increases to where the effects of the Special Theory of Relativity begin to play a role.
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------------------------------ To explain why gold is the color yellow:
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------------------------------ To explain why silver is a colorless mirror?
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------------------------------ Silver reflects all the colors.
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- Gold has 79 protons, one short of a complete shell, before jumping to the next orbital.
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- Silver has 47 protons, one short of a complete shell, before jumping to its next orbital.
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- When an atom is hit by a photon of just the right wavelength, the energy of the photon is absorbed and the electron jumps to a higher energy level shell.
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------------ Ultraviolet light has a wavelength = 100 nanometers, frequency = 3*10^15 cycles per second.
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--------------- Blue light has a wavelength = 400 nanometers, frequency = 0.75 cycles per second.
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- Energy is directly proportional to frequency. Energy = frequency * Planck’s constant of Action, “h’.
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-------------------------------- E = h * f
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-------------------------------- f = c / w
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-------------------------------- c = the speed of light = 3*10^8 meters per second
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-------------------------------- w = wavelength of ultraviolet = 100 nanometers.
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-------------------------------- f = 3 *10^8 / 10^-7 = 3 * 10^15 cycles per second
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-------------------------------- h = Planck’s Constant of Action = 6.625 *10^-34 joule-seconds.
-------------------------------- E = Energy = ( 6.625 *10^-34 ) * (3 * 10^15 )
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-------------------------------- Energy = 19.875*10^-19 Joules
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-------------------------------- Electron volt = 1.6022*10^-19 Joules
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-------------------------------- Energy = 12.4 electron volts
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- ------------------------------ w = wavelength of blue light = 400 nanometers.
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-------------------------------- Energy = 3.1 electron volts
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- In silver the gap between the orbital energies is large, so it takes a photon in the ultraviolet region of the spectrum to cause this transition. ( 100 nm). Higher frequency means higher energy. At the same time, photon's in the spectrum of visible light have lower energy and bounce off. So to the light reaching our eyes silver appears to act as a nearly perfect mirror.
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- In the heavier element gold the relativistic contraction mentioned above for heavier elements begins to raise energy level narrowing the gap between the two levels ( “s” and “d” levels).
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- Now the transition for the electron to jump the gap requires less energy. Less energy means lower frequency for the absorbing photon. Photons of all colors still bounce off but blue light gets absorbed. (400 nm) This yields the reflection in the characteristic golden – yellow color.
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- This phenomenon not only affects color it also allows gold to bind to the inner gas xenon. It also allows the triple bonds between gold and carbon.
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- The heavier elements in the periodic table begin to behave in unexpected ways and, there must be a limit to how many protons can be packed into a nucleus, even for a fleeting moment. It becomes doubtful that elements stacked in the same column will behave similarly.
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- Chemists need not worry about this since they don't get to play with these heavier elements. These elements are the realm of particle physicists who are using particle accelerators to create the heavier elements that decay into the lighter elements in a instant after being created
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------------------ The fun part is there is more to learn.
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- You can see that the energy gap for silver to observe light is higher, 12.4 electron. Period it requires ultraviolet light photon which is outside our visible range. Therefore, we see all the visible light reflected in silver shines like a mirror.
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- The energy gap for gold which is a much heavier element with 79 protons requires less energy in its balance. It absorbs blue light at only 3.1 electron volts. With blue light absorbed yellow orange is reflected giving your eyes that golden color.
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--------------------- And that is why gold is yellow.
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- June 5, 2020 1613 2754
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--------------------- Friday, June 5, 2020 -------------------------
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