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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