chem. 1b – 11/17 lecture

Chem. 1B – 11/17 Lecture

Announcements I• Mastering Chemistry

– Chapter 18 Assignment is due today• Lab

– Completing Experiment 10; Starting Experiment 12• Exam 3:

– Next Tuesday (11/24)– On Electrochemistry and Transition Metals– Electrochemistry part will be similar to exams 1

and 2, while Transition Metals part will be more focused on qualitative/conceptual understanding

Announcements II• Today’s Lecture - Transition Elements

(Ch. 24)• Coordination Compounds

– Ligand types (last time)– Geometries– Naming– Isomers

Chapter 18 ElectrochemistryElectrolytic Cells

• Error in Previous lecture– Electrolysis forces reactions to occur that don’t normally

occur (e.g. if Ecell <0)– For this reason, reduction reactions typically have

negative standard reduction potentials and oxidation reactions typically have positive standard reduction potentials

– I may have said potential closest to zero will occur (NOT TRUE)

– However, the reduction reaction that occurs will have the highest reduction potential (not always negative) and the oxidation reaction will have the lowest reduction potential (reactions must be possible)

Chapter 18 ElectrochemistryElectrolytic Cells

• Example:– a solution contains 0.001 M

CuCl2 and 0.001 M SnCl2. A potential is applied to two inert electrodes. What happens at each electrode?

Power Supply+ -

Reaction E° (V)Cu2+(aq) + 2e- ↔ Cu(s) 0.34Sn2+(aq) + 2e- ↔ Sn(s) -0.14

O2(g) + 4H+(aq) + 4e- ↔ 2H2O(l) 1.23

2H2O(l) + 2e- ↔ 2H2(g) + 2OH-(aq) -0.83 V

Cl2 (g) + 2e- ↔ 2Cl-(aq) 1.36 V

Chapter 24 Transition Metals• Coordination Complex - Geometries

and numbers of ligands– Most Common Geometries:

• Linear (with two ligands)– example: H3N-Ag-NH3

• Square Planar (4 ligand bonds)– example: [PtCl4]2-

• Tetrahedral (4 ligand bonds)– example: [Zn(OH)4]2-

Cl

Cl

Cl

Cl Pt2-

Zn

HOOH

OH

OH


and numbers of ligands– Most Common Geometries:

• Octahedral (with six ligand bonds – note octahedral refers to 8 sides, even though 6 corners)– example: [Co(H2O)6]2+

Co

H2O OH2

H2O

H2OH2O

OH2

Chapter 24 Transition Metals• Coordination Complex - Geometries and

numbers of ligands – Example Questions

– Cobalt(II) forms a complex with three bidentate oxalate ligands. What is the geometry?

– Mercury reacts with 4 I- ligands. What geometries are possible?

– 1 EDTA ligand forms an octahedral complex with Ni2+. EDTA is a _____ dentate ligand


and numbers of ligands – More Questions

– What is the metal oxidation state and number of ligands + ligand bonds for the following compounds:1. Mg[HgCl4]2. [Co(NH3)5Cl]NO3

3. Na2[Cu(ox)2] (ox = C2O42-)

Chapter 24 Transition Metals• Coordination Complex – Naming Compounds

– Naming ligands:• Neutral ligands are given molecule names (e.g.

ethylenediamine) except for:– H2O = aqua– NH3 = ammine– CO = carbonyl

• Anionic ligands are changed from anion:– -ide becomes -o– -ate becomes -ato– -ite becomes -ito

Chapter 24 Transition Metals• Coordination Complex – Naming

Compounds– Naming ligands:

• List names of ligands in alphabetical order before cation name

• Prefixes used to indicate number of ligands (di-, tri-, tetra-, penta-, hexa-) or bis- , tris- if ligand name already has prefix

• Metal names (Depends on complex charge):– Cations (metal name same as in ionic compounds)– Anions (metal – or Latin root – ending in ate)


Compounds– Naming ligands – information for exam:

• Too much to expect you to know all naming rules listed

• Should know all 4th row elements plus d8 to d10 5th and 6th row elements

• Focus on main rules: ligands names plus 3 exceptions at top of guidelines, di- to hexa- prefixes, will give table of Latin roots (e.g. ferrate) if needed


Compounds – Examples:– [Ag(NH3)2]+ =– [Pt(ox)2]2- =– [Fe(NH3)4Br2]Cl = – Tetracyanozincate = – Pentaaquabromonickel(II) = – Sodium diaquatetrachlorovanadate(III) =

Chapter 24 Transition Metals• Coordination Complex – Isomers

– What are isomers?• Have same formula but are somehow different

– Structural isomers• Have different connections between atoms• Examples:- [Fe(NH3)5Br]Cl vs. [Fe(NH3)5Cl]Br (switch of counter

ion with binding ion)- :CΞN: ligands can bind at C (cyano) or N (isocyano)

side


– Stereoisomers• Due to different neighboring ligands• Examples: [Pt(Cl)2(Br)2]2- (square planar)

Pt

Br

ClCl

Br

Trans isomer – like ligands apart

PtBr Cl

Cl

Br

Cis isomer – like ligands together

These will have slight differences in properties (cis has slight net dipole moment while trans does not)


– Stereoisomers – cont.• For tetrahedral compounds, MX2Y2 have only one

isomer (X is same distance to other X and other Ys)

• For octahedral compounds, MX4Y2, also has cis- trans- isomers (guess which is trans)

MY

Y

X

XM

X

X

X X

Y

Y M

X

X X

X

Y

Y


– Stereoisomers – cont.• For octahedral compounds, MX3Y3, also has

fac- (for face) and mer- isomers (for meridinal)

M

Y

X

X X

Y

Y M

X

X Y

X

Y

Y

fac mer


– Stereoisomers – cont.• The stereoisomers mentioned so are geometric

isomers that will have different properties (even if only slight differences)

• Another class is optical isomers, which have (mostly) identical properties; except that each isomer will rotate light differently (and can interact differently with other “chiral” molecules)

• A test for an optical isomer is if its mirror image is non-superimposeable (unique)


– Optical Isomers (examples)• MX2Y2 – two or one optical isomer?• MABCD – two or one optical isomer?

MY

Y

X

X

mirror

MB

C

A

D

120 rotation about Z axis gives back original structure

MB C

A

D

mirror

MY

Y

X

X

Not the same – if we line up A-M-D, B and C are reversed


– Questions1. Which of the following ligands will have linkage

isomers?a) NH3 b) CN- c) H2O d) SCN-

e) C2O42-

2. In what way is [Cr(NH3)5Br]Cl2 different from [Cr(NH3)5Cl]BrCl?

3. How many different isomers are present for the square planar compound [Pt(NH3)2ClBr]?

chem. 1b – 11/17 lecture

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