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HL 12.1 cont… (HL2-5.ppt)

HL Chemistry More on Electron Configuration 12.1.6. HL 12.1 cont… (HL2-5.ppt). So Aufbau, Hund, & Pauli gave us a set of rules that allow us to use the periodic table to predict electron configurations. (See HL 12.1.ppt).

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HL 12.1 cont… (HL2-5.ppt)

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  1. HL Chemistry More on Electron Configuration 12.1.6 HL 12.1 cont…(HL2-5.ppt)

  2. So Aufbau, Hund, & Pauli gave us a set of rules that allow us to use the periodic table to predict electron configurations.(See HL 12.1.ppt) • The important thing to remember is that these rules are extremely useful for elements Z=1 to 40, all of the s block, and all of the non-metals.

  3. Some review • Electrons will fill in lower energy orbitals first. • NOTE - Even though the 3d has a higher energy than the 4s, it is still “underneath” the 4s.

  4. Quantum Numbers • When we talk about “quantum numbers”, • n = prinicapal quantum number and describes the size of the orbital (energy level) • l= angular quantum number and describes the orbital shape (s,p,d,f) • ml = magnetic quantum number and describes the orientation of the orbital in space (x,y,z) • ms= spin (up, down)

  5. Practicing with Aufbau

  6. Why do so many transition elements have a charge of 2+?

  7. Exceptions to the Aufbau process • In the first 40 elements, there are only 2 exceptions when we look at the observed electron configurations and compare them to those predicted by Aufbau. • Predicted • Cr (Z = 24): [Ar] 4s2 3d4 • Cu (Z = 29): [Ar] 4s2 3d9 • Actual • Cr (Z = 24): [Ar] 4s1 3d5 • Cu (Z = 29): [Ar] 4s1 3d10

  8. Exceptions to the Aufbau process • Predicted • Cr (Z = 24): [Ar] 4s2 3d4 • Cu (Z = 29): [Ar] 4s2 3d9 • Actual • Cr (Z = 24): [Ar] 4s1 3d5 • Cu (Z = 29): [Ar] 4s1 3d10 • It has been theorized that this occurs because a 1/2 full (3d5) or completely full 3d (3d10) is more energetically stable than a full 4s. • Energetically stable = less electron repulsion

  9. Exceptions to the Aufbau process • “Once we get beyond atomic number 40, the difference between the energies of adjacent orbitals is small enough that it becomes much easier to transfer an electron from one orbital to another.” * • In other words. They advance beyond our ability to easily predict electron configurations unless the elements are in the s or p blocks. • * taken from http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch6/quantum.html

  10. Take another look

  11. Electron Configurations for Ions • Writing the electron configuration for an ion is relatively easy. Just add electrons for negative ions and subtract them for positive ions. • Most of the time, for s and p block elements you end up with something that ends in p6. • Na+, Mg2+, F- and O2- = [He]2s2 2p6

  12. Electron Configurations for Ions Again the transition metals are a little trickier. Although the 3d orbital is higher energy than the 4s, you must remove the electrons from the 4s first. [Add electrons using Aufbau diagram, remove electrons from highest # energy level first.] This is why some chemists prefer to write electron configurations with 4s after 3d. Fe= [Ar] 4s2 3d6 or [Ar] 3d6 4s2 Fe2+= [Ar] 3d6 Fe3+= [Ar] 3d5

  13. What’s the EC for Ag+?

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