Download Lanthanum has only one important oxidation state in aqueous

CHEM 163
Chapter 23
Spring 2009
http://www.youtube.com/watch?v=kfgtU9DDvdY
Transition Metals
• Large part of inorganic chemistry
Electron Configurations
Zn: [Ar]4s23d10
General form:
Mn: [Ar]4s23d5
[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
Cr: [Ar]4s13d5
x = 1 to 10
Cu: [Ar]4s13d10
Transition Elements: Periodic Trends
Across 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 Trends
Within 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 s electrons!
• Metallic behavior
– Lower oxidation state – ionic bonding
– Higher oxidation state – covalent bonding
• Reducing strength
– All period 4 TMs form H2 from acid (except Cu)
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
"Lanthanum has only one important oxidation state in
• Actinides
aqueous solution, the +3 state. With few exceptions, that
statement tells the whole boring story about the other
fourteen elements" - Pimental & Spratley (1971 textbook)
– Radioactive!
– Some never been seen/only made in labs
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
• Forms bonds that can be ionic or
more covalent
• Can be found in the +1 oxidation state
[Xe] 6s1 4f14 5d10
http://www.youtube.com/watch?v=oL0M_6bfzkU
Silver
• Soft
– Sterling silver is alloyed with Cu to harden
• Highest electrical conductivity of any element
– 63.01 × 106 S/m
(Cu: 59.6 × 106 S/m)
• O.N. = +1
• Doesn’t form oxides in air
• Tarnishes into Ag2S
2Al(s)  3Ag 2S(s) 6H2O(l )  2Al(OH) 3 (s)  6Ag( s) 3H 2S( g )
o
E
 0.86V
Strong reducing agent
Black and White Photography
Film: plastic coated in gelatin containing AgBr microcrystals
Coordination Compounds
TM 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
linear
square planar
tetrahedral
– C.N. = 6
octahedral
Ligands
• Contain donor atoms
– form covalent bond with metal (donates e- pair)
• Monodentate: 1 donor atom
• Bidentate:
2 donor atoms
• Tridentate:
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]
[Pt(NH3)4BrCl] 2+
ClNeed 2Cl[Pt(NH3)4BrCl]Cl2
Potassium amminepentachloroplatinate (IV) 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]
Isomers
Compounds 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
eg
E
dz2
dxy
dx2 - y2
dxz
∆E
dyz
t2g
• Large ∆E: strong field ligand • 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
d orbital splitting
dx2 - y2
E
dz2
dx2 - y2
dxy
dxz
dxy
dyz
dz2
dxy
dxz
Octahedral
dyz
dz2
dx2 - y2
Tetrahedral
dxz
dyz
Square
Planar
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
[Mn(CN)6]4-
Mn2+: d5
E
Weak-field ligand
Strong-field ligand
High spin
Low spin