Chem. 31 - 9/15 Lecture

Chem. 31 - 9/15 Lecture

Chem. 1B 11/17 Lecture Announcements I Lab Last Quiz Monday/Tues on Exp 10, 14 and Chapter 24 No Lab next Wednesday Experiment 10 report due Exam 3 Two weeks (and three lectures) from today On electrochemistry and Chapter 24 Last years exam did not cover last parts

Announcements II Mastering Ch. 24 assignment due 11/26 Todays Lecture Transition Elements (Ch. 24) Bonding in Coordination Complexes - Theory Chapter 24 Transition Metals Optical Isomer Demonstration Show with models of MX2YZ and MWXYZ Chapter 24 Transition Metals Coordination Complex Bonding Theory cont.

To understand how electrons in the d shells influence bonding, we must understand the shapes of d orbitals Two different classes of d orbitals occurs d dxy lies in xy plane Off axes orbitals z z

y x xz z y x dyz y x

Chapter 24 Transition Metals Coordination Complex Bonding Theory cont. Two different classes of d orbitals occurs On axes orbitals dz^2 dx^2 y^2 z z

y x y x Chapter 24 Transition Metals Coordination Complex Bonding Theory cont. E In octahedral binding, because the ligands

bring the electrons, lower energy results when the binding axes orbitals (dz2 and dx2-y2) are UNFILLED Or alternatively, the ligands cause a split in Metal in octahedral complex Free atom energy levels of d shell orbitals D On axis Off axis Chapter 24 Transition Metals Coordination Complex Bonding Theory cont.

How does d orbital splitting affect coordination complexes? Electrons go to low energy states first Example: [Cr(CN)6]3- has 4 1 = 3 d shell electrons they should occupy the three off-axes orbitals On axis Off axis Chapter 24 Transition Metals Coordination Complex Bonding Theory cont. When we add more than 3 electrons (e.g. 4 electrons), there are two possibilities:

fill bottom orbitals first or go to top orbitals Filling depends on D gap (larger leads to low spin states first shown, while smaller leads to high spin states Chapter 24 Transition Metals Coordination Complex Bonding Theory Role of Ligands Particular metals, such as Fe, can form complexes with different properties (e.g. colors or magnetic properties) depending on ligands

Ligands affect size of D gap Strong ligands result in large D gap, while weak ligand results in smaller D gap (with the idea that more tightly held electrons will overlap more with d Chapter 24 Transition Metals Coordination Complex Bonding Theory Role of Ligands and Metal Ligand Strength (see text for full range) CNstrongest NH3 H2O

Cl- Iweakest Weak Field Ligands tend to give high spin states Chapter 24 Transition Metals Coordination Complex Magnetic and Light Absorbing Properties Magnetic Properties:

Compounds or atoms with unpaired electrons are magnetic (since half filled shells will have electrons with the same spin) Example: Fe [Kr]4s23d6 will have 4 E unpaired electrons and is magnetic 3d 4s Other metals, e.g. Zn (d10), are not Chapter 24 Transition Metals Coordination Complex Magnetic Properties cont. Octahedral Complexes will have d

electrons split into to energy states by ligand field Large D gap complexes give rise to low spin states that are less magnetic vs. high spin states Examples: [Fe(CN)6]4- vs. [Fe(Br)6]4large D small D Chapter 24 Transition Metals Coordination Complex Light Absorbing Properties Gap between on- and off-axes d orbitals can also lead to transitions between two states Example: [Cr(CN)6]3

Absorption of light causes electronic transition from low energy to high energy state: Chapter 24 Transition Metals Coordination Complex Light Absorbing Properties cont. Many coordination complexes absorb visible light (lgreen light ~ 525 nm or E = hc/l = 3.8 x 10-19 J) The larger the D gap, the greater the E, and the smaller the l value energy Visible colors go ROYGBIV (red, orange, yellow, green, blue, indigo, violet from longer to shorter

wavelength) Chapter 24 Transition Metals Coordination Complex Light Absorbing Properties cont. Example: [Co(H2O)6]2+ (used for the Drierite color demonstration) Color is pink/purple (but pink is red + white

= seen color because complex absorbs other colors) Using color wheel (text) expected absorbance is in green (measured in Chem 31 as 510 nm) Color wheel used because we see reflected light Chapter 24 Transition Metals Coordination Complex Other Geometries Besides octahedral geometries, tetrahedral and square planar geometries have different overlaps with d orbitals resulting in different d orbital splitting In tetrahedral complexes, the complex can be

positioned (see Fig. 24.17) where ligand bonds interact with off-axis d orbitals (dxy, dxz, and dyz) making these orbitals higher in energy and on-axis d orbitals lower in energy (however Metal in tetrahedral complex Off axis D and high spin states) with small D values On axis Chapter 24 Transition Metals Coordination Complex Other Geometries

In square planar geometry, overlap is most with dx^2 y^2 (but is more complex as shown below) Square planar geometry is common for d8 ions in which dx2 y2 orbitals are unoccupied (low Metal in square planar spin) complex dx2 y2 dxy dZ2 dxz

dyz on axis and off axis in xy plane Chapter 24 Transition Metals Questions 1. Which two d orbitals do octahedral complexes overlap with the most? 2. Which d orbital is there the greatest overlap in square planar complexes? 3. Give the number of unpaired electrons for the following metals in octahedral complexes for low spin states/high spin states a) Fe3+ - octahedral b) Co2+ octahedral

c) Cu2+ - tetrahedral d) Mn3+ - octahedral Chapter 24 Transition Metals Questions cont. 4. Ti3+ is purple while Ti4+ is uncolored. Explain. 5. For which of the following metals in octahedral complexes does the ligand NOT play a role in the number of unpaired electrons? a) Mn2+ b) Fe3+ c) Co2+ d) Ni2+ 6. [Fe(en)3]3+ undergoes a ligand replacement reaction and forms [FeX6]3-. The new complex absorbs at shorter wavelengths. What do we know about the strength of X as a ligand?

Recently Viewed Presentations

  • A537 Space Orientation - Virginia Tech

    A537 Space Orientation - Virginia Tech

    ALTAIR and ALCOR are two contributing space sensors. They are both located on Kwajalein Atoll in the western Pacific. Operated by the U.S. Army Space and Strategic Defense Command, they are used primarily for missile testing. ALCOR is a near...
  • Understanding 2D Structural Analysis

    Understanding 2D Structural Analysis

    Detail of pin-jointed truss connection, approach span to San Francisco-Oakland Bay Bridge. Pin joints are used in older bridges or situations where rotation has to be allowed for due to settlement, or for construction purposes. (San Francisco Bay Area)
  • Sunflower Project Change Agent Network Meeting #4 August

    Sunflower Project Change Agent Network Meeting #4 August

    This field should be used to track the country code (e.g., USA) for the customer's address, whether the customer is inside or outside of the United States. The "Processing Rules" in the file layout will be updated to reflect that....
  • Transform your school with the power of the

    Transform your school with the power of the

    Ensure that your students and educators always have access to the latest feature innovations, with automatic updates for Office 365 and Windows 10, and new technologies such as Minecraft: Education Edition with Code Builder and 3D and Windows Mixed Reality....
  • Prezentace aplikace PowerPoint

    Prezentace aplikace PowerPoint

    flower service. laundry and ironing. taxis and transfers. luggage storage. guide services. ATM. wellness centre (saunas, hot tub, massages) and BeerSpa. Conference rooms. large rooms for up to 1 400 delegates. largestroom to seat up to 1 100 delegates.
  • Chapter 9

    Chapter 9

    This new scatterplot shows that the average life expectancy for a country is related to the number of televisions per person in that country: Slide 9 - * What Can Go Wrong? Make sure the relationship is straight. Check the...
  • HL7 FHIR - School of Engineering

    HL7 FHIR - School of Engineering

    Human Readable. CDA taught HL7 a very important lesson. Even if the computers don't understand 99% of what you're sending, that's ok if they can properly render it to a human clinician
  • Europes Formulation of Fair and Equitable Treatment Europe

    Europes Formulation of Fair and Equitable Treatment Europe

    Each Contracting Party shall accord to such investments full physical security and protection. 2008 Germany Model Article 2(2) (Admission and Protection of Investments) Each Contracting State shall in its territory in every case accord investments by investors of the other...