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Chapter 13

Chapter 13. Electrons in Atoms. Quantum Mechanics http://www.meta-synthesis.com/webbook/30_timeline/310px-Bohr-atom-PAR.svg.png. Better than any previous model, quantum mechanics does explain how the atom behaves.

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Chapter 13

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  1. Chapter 13 Electrons in Atoms

  2. Quantum Mechanicshttp://www.meta-synthesis.com/webbook/30_timeline/310px-Bohr-atom-PAR.svg.png • Better than any previous model, quantum mechanics does explain how the atom behaves. • Quantum mechanics treats electrons not as particles, but as waves (like light) which can gain or lose energy. • But they can’t gain or lose just any amount of energy. They gain or lose a “quantum” of energy. A quantum is just an amount of energy that the electron needs to gain (or lose) to move to the next energy level. Max Planck, another German Nobel Prize winning scientist first came up with this idea.

  3. What the heck is a Quantum?http://www.blogcdn.com/www.slashfood.com/media/2008/08/splenda425.jpghttp://upload.wikimedia.org/wikipedia/commons/e/e9/Sucralose2.png • Think of a quantum as a “packet” of energy, much like a sugar packet at a restaurant. A sugar packet contains a teaspoonful of sugar. • If the electron absorbs energy, it moves to a higher energy level. If it emits (loses) energy, it moves to a lower energy level. • But like Bohr suggested in his model, the electron has to gain or lose exactly the right amount. That amount is a quantum of energy. C12H19O8Cl3 is the formula for sucralose, which is the chemical name for Splenda. That “beast” molecule is sucralose. It’s an Organic compound.

  4. Atomic Orbitalshttp://milesmathis.com/bohr2.jpg • The energy levels in quantum mechanics describe locations where you are likely to find an electron. • These locations are called ORBITALS. Orbitals are “geometric shapes” around the nucleus where electrons are found. • Quantum mechanics can CALCULATE where those orbitals are located. • The 4 different types of orbitals are s, p, d, and f. • Sound familiar?

  5. Atomic Orbitalshttp://courses.chem.psu.edu/chem210/quantum/quantum.html • Of course, you could find an electron anywhere if you looked hard enough. • So scientists agreed to limit these calculations to locations where there was at least a 90% chance of finding an electron. • Think of orbitals  as sort of a "border” for spaces around the nucleus inside which electrons are allowed. No more than 2 electrons can ever be in 1 orbital. The orbital just defines an “area” where you can find an electron. • What is the chance of finding an electron in the nucleus? Yes, of course, it’s zero. There aren’t any electrons in the nucleus.

  6. Atomic Orbitalshttp://www-hep.phys.unm.edu/~gold/phys492/orbitals.gif • Quantum mechanics doesn’t predict SPECIFIC orbits, like the Bohr model does. 3s 2s 1s

  7. Energy Levelshttp://www.chem4kids.com/files/art/elem_pertable2.gif • Quantum mechanics has a principal quantum number. It is represented by a little n. It represents the “energy level” similar to Bohr’s model. • n=1 describes the first energy level • n=2 describes the second energy level • Etc. • Each energy level represents a period or row on the periodic table. It’s amazing how all this stuff just “fits” together. Red n = 1 Orange n = 2 Yellow n = 3 Green n = 4 Blue n = 5 Indigo n = 6 Violet n = 7

  8. Sub-levels = Specific Atomic Orbitals • Each energy level has 1 or more “sub-levels” which describe the specific “atomic orbitals” for that level. • n = 1 has 1 sub-level (the “s” orbital) • n = 2 has 2 sub-levels (“s” and “p”) • n = 3 has 3 sub-levels (“s”, “p” and “d”) • n = 4 has 4 sub-levels (“s”, “p”, “d” and “f”) • There are 4 types of atomic orbitals: • s, p, d and f • Each of these sub-levels represent the blocks on the periodic table. Blue = s block Yellow = p block Red = d block Green = f block

  9. Shapes of These Orbitals(the nucleus is ALWAYS at the center of the orbital) • The s orbital looks like a ball or sphere. • The p orbital looks like a dumb-bell. • These orbitals are all perpendicular to each other. • The d orbitals have two shapes. • 4 of the 5 look like “4-leaf clovers.” • The 5th one looks like a “big dumb-bell” with a “hula-hoop” around the middle. • The shapes of the f orbitals are complex. They are on the next slide, but you don’t need to remember them, nor will they be on the test.

  10. Orbitalshttp://media-2.web.britannica.com/eb-media/54/3254-004-AEC1FB42.gifhttp://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/D_orbitals.svg/744px-D_orbitals.svg.pngOrbitalshttp://media-2.web.britannica.com/eb-media/54/3254-004-AEC1FB42.gifhttp://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/D_orbitals.svg/744px-D_orbitals.svg.png • In the s block, electrons are going into s orbitals. • In the p block, the s orbitals are full. New electrons are going into the p orbitals. • In the d block, the s and p orbitals are full. New electrons are going into the d orbitals. • What about the f block? d p s

  11. f orbitalshttp://antoine.frostburg.edu/chem/senese/101/electrons/faq/f-orbital-shapes.shtml

  12. To Summarize • Complete the chart in your notes as we discuss this. • The first level (n=1) has an s orbital. It has only 1. There are no other orbitals in the first energy level. • We call this orbital the 1s orbital.

  13. “g orbitals”http://jeries.rihani.com/index3.html • Another hypothesis by Glenn Seaborg is that element number 121 will start “the g block.” • The “g” block will be another grouping, similar to the Lanthanides and Actinides, of 18 elements. • Since this is all science fiction, you obviously don’t have to know what g orbitals look like. • A collection of Dr. Seaborg’s most important scientific publications has been published in a book called “Modern Alchemist.” • To date, no elements have been discovered which have 8s electrons. Element 119 is predicted to be the first element in the “8th period.”

  14. Island of Stabilityhttp://www.nytimes.com/1999/02/27/us/glenn-seaborg-leader-of-team-that-found-plutonium-dies-at-86.html • This is another hypothesis from Dr. Seaborg. His thought was that element 114 would be an “island of stability,” especially if it also had 184 neutrons. • Most synthesized elements only last for fractions of seconds. However, in 1998 researchers synthesized element 114 and it lasted for 30 seconds. Perhaps this is the “shore” of the Island of Stability that Dr. Seaborg hypothesized. • The element 114 was made using some of the original Pu-244 that Dr. Seaborg himself made in the early 1940s. They bombarded plutonium with Ca-48 atoms to form some of the new element 114. • Element 114 is now know as Flerovium (symbol Fl)

  15. Island of Stabilityhttp://www.sciencecodex.com/files/Island%20of%20Stability%201.jpghttp://physicsworld.com/cws/article/print/19751 Famous picture of the “Island of Stability” showing the island off in the distance (top right) with 114 protons and 184 neutrons. What would the atomic mass of the island be? An element with Z = 184 is also predicted to be another “island of stability.”

  16. Electron Configurations • What do I mean by “electron configuration?” • The electron configuration is the specific way in which the atomic orbitals are filled. • Think of it as being similar to your address. The electron configuration tells me where all the electrons “live.”

  17. Rules for Electon Configurationshttps://teach.lanecc.edu/gaudias/scheme.gif • In order to write an electron configuration, we need to know the RULES. • 3 rules govern electron configurations. • Aufbau Principle • Pauli Exclusion Principle • Hund’s Rule • Using the orbital filling diagram at the right will help you figure out HOW to write them • Start with the 1s orbital. Fill each orbital completely and then go to the next one, until all of the elements have been acounted for.

  18. Fill Lower Energy Orbitals FIRSThttp://www.meta-synthesis.com/webbook/34_qn/qn3.jpg Each line represents an orbital. 1 (s), 3 (p), 5 (d), 7 (f) • The Aufbau Principle states that electrons enter the lowest energy orbitals first. • The lower the principal quantum number (n) the lower the energy. • Within an energy level, s orbitals are the lowest energy, followed by p, d and then f. F orbitals are the highest energy for that level. High Energy Low Energy

  19. No more than 2 Electrons in Any Orbital…ever.http://www.fnal.gov/pub/inquiring/timeline/images/pauli.jpg • The next rule is the Pauli Exclusion Principal. • The Pauli Exclusion Principle states that an atomic orbital may have up to 2 electrons and then it is full. • The spins have to be paired. • We usually represent this with an up arrow and a down arrow. • Since there is only 1 s orbital per energy level, only 2 electrons fill that orbital. Wolfgang Pauli, yet another German Nobel Prize winner Quantum numbers describe an electrons position, and no 2 electrons can have the exact same quantum numbers. Because of that, electrons must have opposite spins from each other in order to “share” the same orbital.

  20. Hund’s Rulehttp://intro.chem.okstate.edu/AP/2004Norman/Chapter7/Lec111000.html • Hunds Rule states that when you get to degenerate orbitals, you fill them all half way first, and then you start pairing up the electrons. • What are degenerate orbitals? • Degenerate means they have the same energy. • So, the 3 p orbitals on each level are degenerate, because they all have the same energy. • Similarly, the d and f orbitals are degenerate too. Don’t pair up the 2p electrons until all 3 orbitals are half full.

  21. Objective D • NOW that we know the rules, we can try to write some electron configurations. • Remember to use your orbital filling guide to determine WHICH orbital comes next. • Lets write some electron configurations for the first few elements, and let’s start with hydrogen.

  22. Electron Configurations Note that all the numbers in the electron configuration add up to the atomic number for that element. Ex: for Ne (Z=10), 2+2+6 = 10

  23. Electron Configurations of Alkali Metals (and H) • This similar configuration causes them to behave the same chemically. • It’s for that reason they are in the same family or group on the periodic table. • Each group will have the same ending configuration, in this case something that ends in s1.

  24. Emission Spectra = Fingerprint of the Elementshttp://www.cbu.edu/~jvarrian/252/emspex.jpg • Atomic emission spectrum is sometimes called a line spectrum, to distinguish it from the continuous spectrum.

  25. Emission Spectra = Fingerprint of the Elements • Atomic emission spectra are “unique.” You can use the spectrum to identify the element. • It’s like a “fingerprint” which identifies the light as coming from hydrogen, and not from something else. • Scientists can look at light from a distant star and analyze it and determine what types of elements make up that star. • Just by looking at the light! Pretty impressive.

  26. The End

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