CHAPTER 22 THE TRANSITION ELEMENTS
Chapter 22 Overview • A brief overview of producing Iron and Copper metal • The bulk of our time will be spent dealing with one of the more interesting features of transition metals in particular why do transition metals produce the vibrant colors we normally see but don’t think about COLOR
Transition Metals and Color • Main Group metals are All Color-Less i.e. Sodium, Magnesium, Aluminum, Lead, etc… are ALL white solids (sulfur compounds excluded) • So why is it that Transition Metal compounds have color • We need to examine the key difference between Main Group and TM and that has to do with the TM’s unique d-orbitals only to understand how color is possible
Uranium glass is the only kind of glass which can be bound directly to metal once the glass is heated; it is useful for making glass-metal objects
Now for some ground work • Our focus is mainly on the 3d metals, these tend to be the most reactive the therefore the most commonly encountered and studied • General Properties of TM • Electron Configurations • Oxidation Numbers • Radii • Density • Mp • Magnetism • How to make Fe and Cu
PROPERTIES OF THE TRANSITION ELEMENTS Electron Configurations • The most significant factor in the behavior of these elements is the electronic configuration. • The d-group elements have an ns (n-1)d configuration. The number of d-electrons is the most important. • As ions form, the s-electrons are lost first giving a "d" configuration for the ion, ie. d5, d8, etc.
PROPERTIES OF THE TRANSITION ELEMENTS Sulfides phosphates and oxides are most common. • The 5f elements are generally not naturally occurring since they are unstable • The densest elements are Os and Ir due to the Lanthanide contraction (shielding effect of f-block elements not effective). • Some of these elements are quite toxic and are called "heavy-metals".
Lanthanide Contraction • Z* applies the same for successive elements across the f-block as it does in any other period. • Shielding effects diminish across the period due to an increase in the number of protons. • This special name, though not a new phenomena, applies to the Lanthanides and actinides probably in part due to the fairly resent discovery of these elements by Seaborg in the early 1940’s
PROPERTIES OF THE TRANSITION ELEMENTS Oxidation Numbers • The most common oxidation numbers are +2 and +3 for the free ions. • The higher states are usually only seen in combination with oxygen; +7, MnO4-.
Common Oxidation Numbers We’ll find out latter why this is so
PROPERTIES OF THE TRANSITION ELEMENTS Metal Atom Radii • Atom radii decrease across a period due to Z* (effective nuclear) increases across a period because of the effectiveness of electrons in the same subshell to shield the nucleus’s increasing number of protons • The 5th and 6th period metals are almost the same size due to the lanthanide contraction.
TRANSITION ELEMENTS Density • With similar sizes and increasing masses, the densities of the 6th period increase dramatically due to the LC Melting Point • The highest melting point occurs in the middle of each series. • Higher melting points mean higher attractive forces.
Density Periods 4-6
PROPERTIES OF THE TRANSITION ELEMENTS Melting Point • These higher forces occur with higher numbers of unpaired electrons. • The maximum number of unpaired d-electrons is 5, and the maximum number of f-electrons is 7, with each of these occurring when the orbital set is half-filled
TRANSITION ELEMENTS Magnetism • One or more unpaired electron give rise to a property called paramagnetism which is a strong attraction in a magnetic field. • A d-orbital set has 0 to 5 unpaired electrons and an f-orbital set has 0 to 7 unpaired electrons. • Atoms or ions with no unpaired electrons are called diamagnetic.
PROPERTIES OF THE TRANSITION ELEMENTS Magnetism • Ferromagnetism is the ability of the magnetic domains to be permanently aligned by an external magnetic field. • These fields can be eliminated by heating or strong mechanical vibrations.
COMMERCIAL PRODUCTION OF TRANSITION METALS • The metallic elements are found as ores and are mixed with impurities called gangue. • Often, due to size and density, the platinum group (Ru, Os, Rh, Ir, Pd, and Pt) are found in the earths crust together and are difficult to seperate • Once separated, the ore is refined by pyrometallurgy or hydrometallurgy. • The first involves heat and the second involves treatment with aqueous chemicals.
Common Occurrence in Nature No 5f elements, to unstable
Iron Production • The iron ore is reduced to iron using heat and coke. • The coke is primarily carbon and is burned to produce carbon monoxide. Both these chemicals are used in the reduction process. • The silicate impurities are converted to calcium silicate by the reaction of calcium oxide and the SiO2.
Iron Production Here CO2 is reduced further in the presence of C(s) to produce more reducing agent CO(g). Typically limestone, calcium carbonate is added to initiate this process
Iron Production • The molten CaSiO3(l) and the impurities that collect in it are called slag. SiO2(s) + CaO(s) CaSiO3(l) • Phosphorus, sulfur and most of the carbon are removed from the pig iron using a basic oxygen furnace (BOF). • These elements are converted to the corresponding oxides. • Special alloys of steel are prepared by adding other metals like Cr, Ni, and Cu.
Copper Production • Both pyrometallurgy or hydrometallurgy are used to isolate impure copper • The impure copper can be further refined by electrolysis, plating pure copper from solutions of Cu+1. Often iron is involved in this process (reducing any Cu+2 in solution to Cu), but since Fe has a higher potential it will not electroplate out.
COORDINATION COMPOUNDS • Our current understanding of complex like NiCl2 explains the electrostatic interaction between atoms in the complex, primarily speaking, as we find them in the solid state • However, in the solution phase we find TM complexes employ a different type of bonding • Due to TM electron poor nature and their sheer size with five d-orbitals and low energy s-orbital, TM employ bonding not typically seen in main group metals
Simple Main Group metals • Sodium cations bind to water in a ratio to satisfy the cation to dipole charge, often 6 waters attach to a main group metals in solution
Transition Metal Complex • Instead TM compounds form coordination compounds • TM bind “Ligands” to Specific d-orbitals so have very predictable structures
COORDINATION COMPOUNDS • Coordination complexes have ions or molecules bonded to the metal or metal ion in a region called the coordination sphere. • These ions or molecules are called ligands • These ligands are Lewis bases (available lone pair for bonding) or have a charge • Ligands coordinate to empty orbitals on the TM
COORDINATION COMPOUNDS • The general formula, NiCl2.6NH3, is actually [Ni(NH3)6]Cl2, with six ammonia molecules in the inner coordination sphere and two ionic Cl- in the outer coordination sphere. • The number of monodentate ligands attached to the metal is called the coordination number.
COORDINATION COMPOUNDS NiCl2.6NH3, is actually [Ni(NH3)6]Cl2 monodentate ligands Dentate is Latin for teeth; so monodentate means “one bit” Coordination Number of 6
COORDINATION COMPOUNDS • Ligands with two active sights are called bidentate ligands. • A single ligand that could coordinate to six bonding sights on a single metal would be called a hexadentate ligand • Ligands that bind more then one site are called chelating ligands, because of their claw like structure. • The general class for these ligands is called polydentate ligands.
Bidentate Ligands • Ethylene diamine • Oxalate • Acetyl acetone • Phenanthroline
Bidentate Ligands EDTA is a common food preservative
COORDINATION COMPOUNDS Deduce the structures for: [Fe(en)(NH3)4]Cl3 and [Co(phen)(NO)3Cl]Cl2 • Calculate the oxidation number for the metal • How many moles of ions per mole of compound are produced when Ag+ is added?
[Fe(en)(NH3)4]Cl3 • Fe is +3 • 3 moles of AgCl would form
[Co(phen)(NO)3Cl]Cl2 • Co+3 and 2 moles of AgCl
Naming Coordination Compounds 1. Standard (Chem 200) Cation, Anion 2. ***Complex ion or molecule (Chem 202): ligand first in alpha order, followed by name of metal (Ox#), then outer sphere ion. Ligands: • anions with ite or ate change the final “e” to “o” as in nitrate to nitrato. • anions with ide change to “o” as in cyanide to cyano. • molecules uses common name except for water changes to aqua; ammonia to ammine; and CO to carbonyl.
Naming Coordination Compounds Ligands: (Cont.) • multiple simple ligands are prefixed with di, tri, tetra, penta, or hexa. Complex ligands are prefixed with bis, tris, tetrakis, pentakis, or hexakis. 3. If the complex is an anion, the suffix “ate” is added to the metal name [Fe(CO)2-] = dicarbonylironate(0). 4. The name of the metal is followed by the oxidation number of the metal in Roman numerals. PRACTICE THESE RULES !!!!!!!
Naming Coordination Compounds Name K2[Ni(CN)4] Na[Cr(C2O4)2(H2O)2] [Ru(phen)4]Cl3 Tetracyanonickle(II) potassium Diaquabis(oxylato)chromium(III) sodium Tetrakis(phenanthroline)ruthunium(III) chloride
Formula aquachlorobis(ethylenediamine) cobalt(III) chloride Pentacarbonyliron(0) Triaminechloroetheylenediamenecobalt(III) [Co(H2O)(Cl)(en)2]Cl2 Fe(CO2)5 [Co(NH3)3(Cl)(en)]2+
STRUCTURES OF COORDINATION COMPOUNDS AND ISOMERS Common Geometries • Linear, ML2 • Tetrahedral ( not d8), ML4 • Square planar (d8), ML4 • Octahedral, ML6.
Isomerism • Structural isomers have different arrangements of the atoms. • Geometric isomers have the same atom attachments but different geometrical arrangements. • Stereoisomers that have a special difference based on chirality are called optical isomers, which have mirror image forms that cannot be superimposed.
Geometric Isomerism • Tetrahedral, none • Square planar and octahedral, cis and trans • Octahedral, fac and mer. • See various Figures.
Geometric Isomerism Cis Trans Square Planar