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Electrons!!! They light up my life! Remember Rutherford? He figured out that: Atoms are mostly empty space Atoms have a very small, dense, positively charged nucleus. These things were very nice to know; however they didn’t explain how atoms behaved in chemical reactions. But he had a student by the name of Neils Bohr who was more of a physicist than chemist. Bohr-ing discoveries So Bohr looked at electrons to see why atoms behave as they do: He figured out that: Electrons occupy energy levels, like rungs on a ladder. Electrons aren’t found between levels. In other words, electrons are quantized and only have certain amounts of energy. These quanta of energy are released as packets of light energy called photons Energy levels are not evenly spaced However, Bohr’s theories only explained a hydrogen atom. More Bohr You’re probably (or hopefully) wondering: “How did Bohr figure out this energy level/ladder stuff?” Bohr knew about the electromagnetic (EM) spectrum Bohr and the EM Spectrum When Bohr heated up some hydrogen gas it produced this spectrum What does this spectrum for hydrogen tell you? Hint: There are individual lines, not a continuous spectrum. The Entire Spectrum for Hydrogen Other scientists discovered the other spectral lines for Hydrogen, as seen here: The Lyman series are the electron drops that produce ultraviolet radiation. The Bahmer series produces visible light. The Paschen series produces infrared light Electron energy The amount of energy an electron absorbs or releases can be determined by an equation derived by Max Planck. Energy = Planck’s constant x frequency E = hv Planck’s constant = 6.6262 x 10-34 Joule-seconds A Joule is a measurement of energy. There are 4.2 kilojoules of energy in one food calorie. Some energy problems Suppose an electron produces light with a frequency of 5 x 1014 Hz, how much energy is being released by the electron falling? E = hv E = 6.6262 x 10-34 J-sec x 5 x 1014 Hz = 3.3131 x 10-19 Joules With sig figs, that would be 3 x 10-19 Joules Suppose an electron produces light with a frequency of 7.5 x 1014 Hz, how much energy is being released by the electron falling? E = hv E = 6.6262 x 10-34 J-sec x 7.5 x 1014 Hz = 4.96965 x 10-19 Joules With sig figs, that would be 5.0 x 10-19 Joules A more complicated math problem Suppose an electron produces light with a wavelength of 700 nm (700 x 10-9 meters). How much energy is being released? Since you have wavelength, you need to change to frequency first. Remember c = λv, or v = c/λ So v = (300,000,000 m/s)/(700 x 10-9 meters) = 4 x 1014 Hz E = hv E = 6.6262 x 10-34 J-sec x 4 x 1014 Hz = 2.65048 x 10-19 Joules With sig figs, that would be 3 x 10-19 Joules Heisenberg and Shrodinger These two figured out that the electrons were found in areas of probability instead of in planetary like orbits (as Bohr proposed). The reason the electrons must be in areas of probability is because they are…they are… they are... particles and waves at the same time!?! So Bohr’s energy levels are still okay, but the electrons are in areas of probability (orbitals). The Quantum Mechanical Model Our current model of the atom is the quantum mechanical model. It includes the following propositions: Electrons are quantized: They have discreet amounts (1 or 2 or 3, but not between 1 or 2 or 3) of energy since they are only found at certain energy levels. Electrons behave as waves and, therefore, are found in areas of probability called orbitals Orbitals are areas where electrons are likely to be found. Electrons and where they live As Bohr said, electrons can be found on different energy levels, or at different distances from the nucleus. These energy levels are numbered 1,2, 3, etc. (Floors in an apartment building) The energy levels also have sublevels (Apartments in an apartment building) An energy level has the same number of sublevels: Level 1 has 1 sublevel, level 2 has 2 and so on. The sublevels are as follows: s, p, d, f. Each sublevel makes a block on the periodic table And each sublevel has orbitals (Rooms in the apartments). Each orbital holds 2 electrons. S sublevel has 1 orbital, so it holds 2 electrons P sublevel has 3 orbitals, so it holds 6 electrons D sublevel has 5 orbitals, so it holds 10 electrons F sublevel has 7 orbitals, so it holds 14 electrons Orbitals And each sublevel has orbitals (Rooms in the apartments). Each orbital holds 2 electrons. S sublevel has 1 orbital, so it holds 2 electrons P sublevel has 3 orbitals, so it holds 6 electrons D sublevel has 5 orbitals, so it holds 10 electrons F sublevel has 7 orbitals, so it holds 14 electrons Some rules for figuring out electron configurations Aufbau Principle: Electrons fill the lowest energy levels first. Pauli Exclusion Principle: Up to 2 electrons can fill an orbital and the electrons must have opposite spins. Hund’s Rule: Each orbital of an energy sublevel gets one electron before putting a second electron in an orbital of the energy sublevel. How to figure out an electron configuration: Periodic Table Edition Just fill in things as you go… Label the blocks on your periodic table. Energy level is the period. Except on d block you subtract 1 from the period to get the energy level In f block you subtract 2from the period to get the energy level (I’ll never have you do an f block element on a test. The number over in the block is how many electrons the element has in that sublevel. Let’s do some electron configuratin’!!! Oxygen Aluminum Sodium Chromium Strontium Bromine Iron Uranium Energy Levels This is how I recheck my work. Wave stuff The three most important characteristics of waves for you to know are: Wavelength: How far it is between crests of waves Measured with units of length like meters or nanometers Frequency: How often waves pass by. Measured in Hertz (Hz) or megahertz, or kilohertz Wavelength and frequency are inversely proportional. The product of wavelength and frequency equals a constant Constant = wavelength (λ) x frequency (Υ) c = λΥ The longer the wavelength the lower the frequency The shorter the wavelength the higher the frequency Waves and Energy If you look at the electromagnetic spectrum, what can you tell me about the relationship between wavelength and energy? Shorter wavelength = higher energy What about the relationship between frequency and energy? Higher frequency = higher energy Waves, energy, light and electrons Hopefully you remember that when you “excite” an electron, it jumps and then releases light as it falls back down… If I can see the light I can tell the frequency I can tell how much energy was released So I can tell how far the electron jumped