Home > Chemistry > Bonus Lecture: Principles of Chemical Science Lecture 27 Notes

Bonus Lecture: Principles of Chemical Science Lecture 27 Notes

Overview

I saw this class in the playlist on the right of our usual lectures.  I was excited to see coordination complexes covered and decided to go ahead and pull it.

This is an introduction to transition metals, where the d orbitals are found.  The lecture is free but costs 51 minutes.  Annoyingly, the camera follows the teacher but not the notes.  Please correct this if any cameramen are reading!  She is pretty but I want to learn chemistry:

Details

This is the center portion of the periodic table, where the 10 d electrons are found.

A positive metal ion attracts electron density, usually ripping off electrons from other atoms.  Donor atoms are called ligands as in “ligands coordinated to the atom.”

Lewis bases donate lone pairs, lewis acids accept lone pair electrons.  The transition metal usually acts as the acceptor.

Coordination number (Cn) is the number of ligands bonded to the metal.  Cns vary from 2 to 12 but 6 is the most common.  Where are the atoms with respect to the d orbitals?

Cn = 6 is octahedral geometry.

Cn = 5 is trigonal bipyramidal or square pyramidal

Cn = 4 is square planar or tetrahedral

Cn = 3 is trigonal planar

Cn =2 is linear

Transition metals can “chelate” or bind a metal at more than one site.  Unidentate is bonding at one site.  Chelates are ligands that can bind at more than one site.  Above one is a chelate.  Bidentate is two points.

Metal chelates are very stable.  This is a thermodynamic effect, an entropic factor.  Waters will be released.  Vitamin B12 is a chelate, with cobalt in the middle.  Dorothy Hodgin got a nobel prize for Vitamin B12 x ray identification.

This teacher, Catherine Drennan, is a crystallographer.  She claims not everyone can do it.

EDTA is also a chelate.  There are 6 available sites.  Cn = 6 so its octahedral geometry and hexadentate.

For EDTA, before chelation we have 6 water molecules floating around it.  One molecule of EDTA binds forming the hexadentate complex, releasing all 6 water molecules.  Now there are 6 free molecules, creating disorder.  S is entropy which is very positive here.  Non chelating ligands are released, usually water.

There are many practical uses.  Paint used to contain lead.  EDTA is given to chelate the lead.  It can however take other metals out of the body.  It’s also a food additive.  EDTA is added for freshness, so it removes metals that bacterias use for biological catalysts.

Cleaning as well.  Calcium must be chelated out.  ‘

Robert Black used freshmen chemistry to make money.  His wife asked him to clean the tub.  He came up with an idea to use chelators, you squirt the surface of the tub/sink.  Surfactants, alcohol, and chelator.  Alcohol to dissolve oils.

to help the stuff run off.

She also mentions vampire movies.  She talks about Blade and exploding vampire heads.  Blood has iron, remove the iron, vampires die.

Geometry isomers can have very different properties.  [PtCl2(NH3)2] is square planar.  Cis-platinum and trans-platinum have very different properties.  You want the atoms on the same side for cis-platen’s cancer treatment.  Binding to DNA, it stops transcription.  This is often used for prostate cancer.

Optical isomers are enatimers.  If there is a mirror plane, they are not identical and are chiral.

How many d electrons are involved?  You’ll need the periodic table and oxidation number.

[Co(NH3)6]+3

NH3 = 0, Co = +3, d count = group 9 – ox number 3 = 6, d6.

[Ni(CO)4]

CO = 0, Ni = 0, d count = group 10 – ox number 0 = 10, d 10.

[Co(H2O)2(NH3)(Cl)3]-1

H2o = 0, Cl = -1 x 3, NH3 = 0, Co = +2, d count = 9 – 2 = 7, d7.

D orbitals have barbell like shapes.  There are 5 d orbitals, each holding 2.  dz2, dxy, dyz, dx2-y2 is the donut, dxz.  Knowing this is important to knowing where electrons are.

Review

G = H-TS

PV = nRT

Lewis acids accept, lewis bases donate electrons.

s 2, p 6, d 10, f 14

LEO goes GER

OIL RIG

IGL: high temp, low pressure, point source, random motion, elastic collisions

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