chem 163 chapter 23

CHEM 163

Chapter 23

http://www.youtube.com/watch?v=kfgtU9DDvdY

Spring 2009

Transition Metals• Large part of inorganic chemistry

Electron ConfigurationsZn: [Ar]4s23d10 Mn:

[Ar]4s23d5

Cr:

[Ar]4s13d5 Cu:

[Ar]4s13d10

General form: [noble gas] ns2 (n-1)dx

n= 4 or 5 x = 1 to 10

[noble gas] ns2 (n-2)f14 (n-1)dx

n= 6, or 7 x = 1 to 10

Transition Elements: Periodic TrendsAcross a period:– Atomic size: decreases, then remains constant

• d e- are filling inner orbitals • Shield outer e- from nuclear pull

– Electronegativity: increases slightly

– Ionization Energy: increases slightly• d e- shield nuclear pull effectively

Transition Elements: Periodic TrendsWithin a group:– Atomic size: no change

• Increase in size between periods• Increase in nuclear charge (32!) decreased size

– Electronegativity: increases slightly• More electronegative than elements in lower periods

(increasing nuclear charge)– Ionization Energy: increases

• Small increase in size; large increase in nuclear charge

Density– Across a period: increase, then level off– Down a group: increase dramatically

• Size constant

Chemical Properties• Multiple oxidation states– Electrons close in E (all ready for bonding)– Highest oxidation state = group number for 3B(3) to 7B(7)– +2 oxidation state is common

• Metallic behavior– Lower oxidation state – ionic bonding– Higher oxidation state – covalent bonding

• Reducing strength– All period 4 TMs form H2 from acid (except Cu)

s electrons!

Color!• To absorb visible light, e- need a nearby higher E level• Main group ionic compounds have full outer shells

– Next E level far away

• Only colorless TM compounds include:– Sc3+, Ti4+, Zn2+

compounds of period 4 transition metals

Magnetic Properties• Paramagnetic:

unpaired electrons

• Diamagnetic: all e- paired

Attracted to an external magnetic field

Unaffected by an external magnetic field

• Most main-group metal ions have full shells• Compounds with TM ions typically have unpaired e-• Compounds with TM ions with d0 or d10 are

diamagnetic

Inner Transition Elements• Lanthanides– “rare earth elements”

• Not actually rare– 14 elements– Cerium (Z = 58) through Lutetium (Z = 71)– Silvery, high-melting (800-1600 °C)– Applications:

• Tinted sunglasses• strongest known permanent magnet (SmCo5)• catalysts

• Actinides– Radioactive!– Some never been seen/only made in labs

"Lanthanum has only one important oxidation state in aqueous solution, the +3 state. With few exceptions, that statement tells the whole boring story about the other fourteen elements" - Pimental & Spratley (1971 textbook)

Chromium

• Protective coating of Cr2O3 forms in air

• Exists in several oxidation states– CrO4

2- : yellow

– Cr2O7 2- : orange

– CrO3 : deep red

– Cr3+ : blue/violet– Cr(OH)4 - : green

• Cr (s) and Cr2+ : strong reducing agents• Cr6+ in acid: strong oxidizing agent

Manganese

• Used in steel alloys• more easy to work • tougher

• Several oxidation states• Mn with oxidation states > +2 are good oxidizing agents• Does not easily oxidize in air• Already stable with d5 configuration

Mercury

http://www.youtube.com/watch?v=oL0M_6bfzkU

• Forms bonds that can be ionic or more covalent

• Can be found in the +1 oxidation state[Xe] 6s1 4f14 5d10

Silver• Soft

– Sterling silver is alloyed with Cu to harden

• Highest electrical conductivity of any element– 63.01 × 106 S/m

• O.N. = +1• Doesn’t form oxides in air• Tarnishes into Ag2S

(Cu: 59.6 × 106 S/m)

)(OH6)(SAg3)(Al2 22 lss )(SH3)(Ag6)(Al(OH)2 23 gss

V86.0oEStrong reducing agent

Black and White PhotographyFilm: plastic coated in gelatin containing AgBr microcrystals

Coordination CompoundsTM form coordination compounds or complexes– Complex ion

• central metal cation• ligands

(Anions or molecules with lone pairs)

– Counter ions• maintain charge neutrality

Coordination compounds dissociate in water

Complex Ions• Coordination Number:– # of ligand atoms bonded directly to the TM ion– Most common C.N. = 6

• Geometry:– C.N. = 2

– C.N. = 4

– C.N. = 6

linear

square planar

tetrahedral

octahedral

• Contain donor atoms– form covalent bond with metal (donates e- pair)

• Monodentate:

• Bidentate:

• Tridentate:

Ligands

1 donor atom

2 donor atoms

3 donor atoms

Coordination Compound Formulas• Cation written before anion• Neutral ligands written before anionic ligands• Whole ion written in brackets– may be cationic or anionic

• Charge of cation(s) balanced by charge of anion(s)

Tetraaminebromochloroplatinum(IV) chloride

[cation] Cl-

[Pt(NH3)4BrCl] 2+ Need 2Cl-

Potassium amminepentachloroplatinate (IV)

[Pt(NH3)4BrCl]Cl2

K[Pt(NH3)Cl5]

Naming Coordination Compounds• Name cation first, then anion• Within the complex ion, ligands named (in alphabetical

order) before TM• Ligands– most molecules names stay same– anions lose –ide; add –o – Prefix tells how many

• If ligand name already contains prefix, use:bis (2); tris (3); tetrakis (4)

• TM oxidation state in parentheses (if multiple possible)• If complex ion is an anion, change to –ate

K[Pt(NH3)Cl5]

IsomersCompounds with same chemical formula, different properties• Constitutional Isomers:

– Same atoms connected differently– [MA5B]B2 and [MA3B3]A2

• Linkage Isomers:– Same atoms, same complex ion, ligand connected differently– Nitrite ligand: NO2

-

Geometric Isomers• Same ligands, arranged differently around TM• cis- and trans-

Optical Isomers• Physically identical except rotate polarized light differently• “enantiomers” (like hands)

Bonding in Complexes

• Coordinate covalent bond: – Both electrons from one atom

• Complex ion is a Lewis adduct– Ligand: Lewis base– Metal: Lewis acid

• Crystal Field theory– Describes d-orbital energies (TM) as ligands approach

d orbitals dxy dxz dyz dz2 dx2 - y2

• In an atom- all d orbitals have same E• When part of coordination compound, E changes happen

Crystal Field Splitting

E

dxy dxz dyz

dz2 dx2 - y2

∆E

• Large ∆E: strong field ligand

eg

t2g

• Small ∆E: weak field ligand

Splitting of d orbitals

• Minimized energy when ligands approach TM on axes• dxy dyz dxz lie between approaching ligands – minimal repulsion

dx2 - y2

dxy

dz2

d orbital splitting

E

dxy dxz dyz

dz2 dx2 - y2 dxz dyz

dxz dyz

dz2

dxy

dx2 - y2

Octahedral Square Planar

Tetrahedral

Color of TM• We see reflected/transmitted colors– Absorbed complementary color

• For a given ligand, color depends on TM oxidation state• For a given metal, color depends on ligand field strength

Magnetic Properties of TM[Mn(H2O)6]2+ Mn2+: d5

E

[Mn(CN)6]4- Mn2+: d5

Weak-field ligand Strong-field ligand

High spin Low spin