CHEM 163 Chapter 23 Spring 2009

Transition Metals Large part of inorganic chemistry

Electron Configurations Zn:[Ar]4s 2 3d 10 Mn: [Ar]4s 2 3d 5 Cr:[Ar]4s 1 3d 5 Cu:[Ar]4s 1 3d 10 General form:[noble gas] ns 2 (n-1)d x n= 4 or 5x = 1 to 10 [noble gas] ns 2 (n-2)f 14 (n-1)d x n= 6, or 7x = 1 to 10

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 Metallic behavior – Lower oxidation state – ionic bonding – Higher oxidation state – covalent bonding Reducing strength – All period 4 TMs form H 2 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: – Sc 3+, Ti 4+, Zn 2+ 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 d 0 or d 10 are diamagnetic

Inner Transition Elements Lanthanides – “rare earth elements” Not actually rare – 14 elements – Cerium (Z = 58) through Lutetium (Z = 71) – Silvery, high-melting ( °C) – Applications: Tinted sunglasses strongest known permanent magnet (SmCo 5 ) 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 Cr 2 O 3 forms in air Exists in several oxidation states – CrO 4 2- : yellow – Cr 2 O 7 2- : orange – CrO 3 : deep red – Cr 3+ : blue/violet – Cr(OH) 4 - : green Cr (s) and Cr 2+ : strong reducing agents Cr 6+ 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 d 5 configuration

Mercury Forms bonds that can be ionic or more covalent Can be found in the +1 oxidation state [Xe] 6s 1 4f 14 5d 10

Silver Soft – Sterling silver is alloyed with Cu to harden Highest electrical conductivity of any element – × 10 6 S/m O.N. = +1 Doesn’t form oxides in air Tarnishes into Ag 2 S (Cu: 59.6 × 10 6 S/m) 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 – 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(NH 3 ) 4 BrCl] 2+ Need 2Cl - Potassium amminepentachloroplatinate (IV) [Pt(NH 3 ) 4 BrCl]Cl 2 K[Pt(NH 3 )Cl 5 ]

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(NH 3 )Cl 5 ]

Isomers Compounds with same chemical formula, different properties Constitutional Isomers: – Same atoms connected differently – [MA 5 B]B 2 and [MA 3 B 3 ]A 2 Linkage Isomers: – Same atoms, same complex ion, ligand connected differently – Nitrite ligand: NO 2 -

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 d xy d xz d yz dz2dz2 d x 2 - y 2 In an atom- all d orbitals have same E When part of coordination compound, E changes happen Crystal Field Splitting E d xy d xz d yz dz2dz2 d x 2 - y 2 ∆E Large ∆E: strong field ligand egeg t 2g Small ∆E: weak field ligand

Splitting of d orbitals Minimized energy when ligands approach TM on axes d xy d yz d xz lie between approaching ligands – minimal repulsion

d x 2 - y 2 d xy dz2dz2 d orbital splitting E d xy d xz d yz dz2dz2 d x 2 - y 2 d xz d yz d xz d yz dz2dz2 d xy d x 2 - y 2 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(H 2 O) 6 ] 2+ Mn 2+ : d 5 E [Mn(CN) 6 ] 4- Mn 2+ : d 5 Weak-field ligandStrong-field ligand High spinLow spin