Exploring Transition Metals and Ionic Compounds
Learn about the characteristics, reactivity, and electron configurations of transition metals, including exceptions to the AUFBAU principle. Discover how transition element sizes, oxidation states, and ionization energies play a role in their chemistry.
Exploring Transition Metals and Ionic Compounds
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Presentation Transcript
CH# 17 Coordination Chemistry
Transition Metals • Transition metals show similarities within a period and a group, different than representative elements • Differences can be attributed to the fact that when electrons are added across a period the valence electrons are not effected. • Therefore group designations are not important here • Behave as metals, strong metallic character
Transition Metals • Some differences • Melting point, Tungsten melts 3400°, while mercury -39°C • Some soft, like sodium that can be cut with a butter knife • Reactivity • Some spontaneously react with oxygen like iron, which flakes off • Others react with oxygen to make a colorless tight fitting oxide, such as chromium, thus protecting the surface • Some metals are inert to oxygen such as gold, silver and platinum
Transition Metals Ionic compound formation • More than one oxidation state is often observed • Cations, often are complexes, which we will discuss later in this chapter • Most compounds are colored, since complexes absorb visible light • Many compounds are paramagnetic This chapter will deal specifically the first row transition elements
Electron Configurations Exceptions to the AUFBAU principle • Cr prefers a half full d as opposed to a full 4s, thus 4s13d5 • Copper prefers a full 3d as opposed to a full 4s, thus 4s13d10 • This half filled, or filled d orbital, is used most of the time to explain this, but other transition metals do not follow this trend.
Electron Configurations Many texts explain AUFBAU exceptions of chromium and copper as a half full sublevel are more stable than a full 4 s sublevel, or for copper that a full d-sublevel is more stable than a half full 4s • Why is this not the case in periods below? • The 4 s and the 3 d orbitals are of about the same energy or nearly degenerate. Perhaps there is a larger repulsive force in the 4s than in 3d orbitals. • I do not think any one knows, but it is good to think and create right?
Electron Configurations 4d and 5d Transition Series • See the size relation on next slide • Decrease in size as we go from left to right, stopping when the d is half full • Significant drop in size going from 3d to 4d, but 4d and 5d remain about the same size • Called Lanthanide contraction • Adding f electrons below the d and the valence shell shel electrons (shielding) • Thus the effect of the increasing size by adding another shell of electrons, which is normally in transition and representative elements, is offset by the shielding of the added f electrons
Oxidation States and IE • See common oxidation states on Next slide • The maximum oxidation state for each transition element going across the row is what we would get by losing both 4s and 3d electrons, toward the end only 2+ is observed, the explanation is that as the effective charge increases thus holding the d electrons tighter. • Reducing ability, decreases from left to right
Ionization Energies Red dot- First ionization energy (removing 4s e) Bluedot-third ionization energy removing 3d electron, closer to nucleus, thus more tightly held
First-row Transition Metals Scandium • Rare element most always +3 oxidation state, ie ScCl3, Sc2O3 • Chemistry of scandium resembles the lanthanides • Colorless compounds • Diamagnetic • Color and magnetic properties are due to d electron, Sc has no d electrons
First-row Transition Metals Titanium • Found in the earths crust (0.6%) • Low density and high strength • Fairly inert, and is used in pipes • TiO2 is a very common white pigment • Common oxidation state is +4
First-row Transition Metals Vanadium • Found in the earth’s crust about 0.02% • Common oxidation state is +5 • Since vanadium contains d electrons solutions are colored • VO2+ is yellow with V in the +5 oxidation state • VO2+ is blue with V in the +4 oxidation state • V3+ is blue-green with V in +3 oxidation state • V2+ is violet with V in +2 oxidation state
First-row Transition Metals Chromium • Rare, but important industrial chemical • Chromium oxide is colorless, tuff, and holds to the metal strongly, almost invisible • Chromium compounds in solution are also colored since they contain d electrons • Common oxidation states are +2, +3 and +6 • Chromium VI is an excellent oxidizing agent! Why? • Strength increases as acidity increases • Chromerge very good glassware cleaning agent • What would we predict for Cr metal? • Cr6+ in the form of dichromate ion usually reduces to the +3 state
First-row Transition Metals • Iron • Is the most abundant heavy metal (4.7%) in earth’s crust, Why? • Common oxidation states +2 and +3 • Iron solutions are colored since they contain d electrons • Cobalt • Relatively rare • Hard bluish-white metal • Common oxidation states are +2 and +3 • Oxidation states +1 and +4 are also known • Typical color is rose color
First-row Transition Metals • Nickel • Most always the +2 oxidation state • Sometimes +3 oxidation state • Emerald green colored solutions
First-row Transition Metals • Copper • Quite common, as sulfides, arsenides, chlorides and carbonates • Great electrical conductor second only to silver • Widely used in plumbing • Found in bronze and brass • Not highly reactive will not reduce H+ • Slowly oxides in air, producing a green oxide • Common oxidation state +2, +1 is also known • Aqueous solution are bright Royal blue • Quite toxic, used to kill bacteria • Paint often contains copper so algae do not grow on the paint
First-row Transition Metals Zinc • Quite common in earths crust, usually as ZnS • Great reducing agent, quite reactive • Oxidation state of +2 • Used to galvanize steel
Coordination compounds • Transition metals form coordination compounds • Transition metals contain a complex ion attached to ligands via coordinate covalent bonds • Coordination compounds are usually colored and paramagnetic
Coordination compounds • Complex ions, usually inside [ ] • Transition coordinately bonded to Lewis bases, the metal is acting as a Lewis acid • Example [CoCl(NH3)5]2+ this cation can combine with anions to balance the charge, thus forming a salt • Ligands are the groups of atoms bonded with a coordinate covalent bond to a transition metal, or a transition metal ion.
Coordination compounds • Alfred Werner was the father of coordination chemistry • Alfred Werner called the salt formation the primary valence • The secondary valence is the formation of the complex ion itself • The compound above has a secondary valence of 6, since it combines with 6 ligands • The primary valence is +2 since that is what needs to be neutralized with anions. • Now days the secondary valence is called the coordination number and the primary valence is called the oxidation state
Coordination Compounds • The number of coordinate covalent bonds formed by the metal ion and the ligands • Variance of 2-8, with 6 being most common. • Geometrical Shape • Ligands = 2, then linear • Rare for most metals • Common for d-10 systems (Cu+, Ag+, Au+, Hg2+) • Ligands = 3, Trigonal planar • Rare for most metals • Is known for d-10 systems (example HgI3‑)
Coordination Compounds • Geometrical Shape • Ligands = 4, then tetrahedral, or square planar • Tetrahedral structure is observed for nontransition metals, BeF42- and d-10 inons such as ZnCl42-, FeCl4-, FeCl42- • Square planar is found with second and third row transition metals with d-8 Rh+, Pd2+ -Ligands = 5 • trigonalbipyramid • square pyramidal
Coordination compounds • Geometrical Shape • Ligands = 6, then octahedral and prismatic (rare) • Ligands = 7 Relatively uncommon, pentagonal • Second and third row transition metals, lanthanides , and actinides • Lignads = 8, relatively common for larger metal ions, common geometry antiprism and dodecahedron • Lignads = 9 larger metal ions, geometry tricappedtrigonal prism [Nd(H2O)9]3+
The Ligand Arrangements for Coordination Numbers 2, 4, and 6
Ligands • Atoms attached to a transition metal via coordinate covalent bonds • They are Lewis bases, since they donate a pair of electrons to the transition metal. • Ligands are classified relative to how many attachments to the metal • Monodentate forms one bond to a transition metal • Lignads forming more than bond are called chelating ligands, or chelates
Ligands • Ligands are classified relative to how many attachments to the metal • Bidentate, a chelating agent, forms two bonds, examples: • Oxalate • Ethylenediamine • Polydentate forms more than two bonds. • Diethylenetriamine • Ethylenediaminetetraacetic acid
Ligands • EDTA is used to remove lead from animals • More complicated ligands are found in biological compounds • EDTA is used as a preservative to tie up substances that could catalyze decomposition of food products
Nomenclature • Cationic species named before anionic species • Within a complex, the ligands are named first in alphabetical order followed by the metal atom • the names of anionic lignads end in the suffix -o- • chloride ----->chloro • cyanide ----->cyano • oxide ----->oxo • Hydroxide -->hydroxo • Oxalate------>oxalato • Sulfate ------>Sulfato • Nitrate ------>Nitrato
Nomenclature • lignads whose names end in -ite or ate become -ito and ato respectively • carbonate ----> carbonato • oxalate-----> oxalato • thiosulfate ----> thiosulfato • Sulfite -----> sulfito • neutral lignads are given the same names as the neutral molecule • exceptions, ammonia (ammine), water (aqua), carbon monoxide (Carbonyl), and NO (nitrosyl)
Nomenclature • When there is more than one of a particular ligand, number is specified by di, tri, tetra, penta, hexa, and so forth. when confusion might result, the prefixes bis, tris and tetrakis are employed e.g. bis(ethylenediaminne) • negative (anionic) complex ions always end in the suffix -ate • aluminum -----> aluminate • chromium -----> chromate • manganese ------> manganate • coblat ------> cobaltate • For some metals the -ate is appended to the Latin stem always appears with
Nomenclature • the common English name for the element • iron ----> ferr ------> ferrate • copper ---> cupra -----> cuprate • lead ----> plumb -----> plumbate • silver ---> argent ----> argentate • gold ---> aur ----> aurate • tin ----> stann -----> stannate • the oxidation number of the metal in the complex is written in roman numerals within parentheses following the name of the metal
Nomenclature • Formula writing • Metal is first, followed by anions, then neutral molecules • If two or more anions or neutral molecules are present, then use alphabetical order. • Nomenclature Examples • tetracyanonickelate(II) ion • tetramminedichlorocobalt(III) ion • sodium hexanitratochromate(III) • diamminesilver(I) ion
Nomenclature • Formula writing • Metal is first, followed by anions, then neutral molecules • If two or more anions or neutral molecules are present, then use alphabetical order. • Nomenclature Examples • tetracyanonickelate(II) ion [Ni(CN)4]2- • tetramminedichlorocobalt(III) ion • sodium hexanitratochromate(III) • diamminesilver(I) ion
Nomenclature • Formula writing • Metal is first, followed by anions, then neutral molecules • If two or more anions or neutral molecules are present, then use alphabetical order. • Nomenclature Examples • tetracyanonickelate(II) ion [Ni(CN)4]2- • tetramminedichlorocobalt(III) ion [CoCl2(NH3)4]+ • sodium hexanitratochromate(III) • diamminesilver(I) ion
Nomenclature • Formula writing • Metal is first, followed by anions, then neutral molecules • If two or more anions or neutral molecules are present, then use alphabetical order. • Nomenclature Examples • tetracyanonickelate(II) ion [Ni(CN)4]2- • tetramminedichlorocobalt(III) ion [Co(NH3)4Cl2]+ • sodium hexanitratochromate(III) Na3[Cr(NO3)6] • diamminesilver(I) ion
Nomenclature • Formula writing • Metal is first, followed by anions, then neutral molecules • If two or more anions or neutral molecules are present, then use alphabetical order. • Nomenclature Examples • tetracyanonickelate(II) ion [Ni(CN)4]2- • tetramminedichlorocobalt(III) ion [CoCl2 NH3)4]+ • sodium hexanitratochromate(III) Na3[Cr(NO3)6] • diamminesilver(I) ion [Ag(NH3)2]+
Nomenclature • Formula writing • Metal is first, followed by anions, then neutral molecules • If two or more anions or neutral molecules are present, then use alphabetical order. • Nomenclature Examples • tetracyanonickelate(II) ion [Ni(CN)4]2- • tetramminedichlorocobalt(III) ion [CoCl2(NH3)4]+ • sodium hexanitratochromate(III) Na3[Cr(NO3)6] • diamminesilver(I) ion [Ag(NH3)2]+
Nomenclature Name the following: • [Ni(H2O)6]Cl2 hexaaquanickel(II) chloride • [Cr(en)3](ClO3)3 • K4[Mn(CN)6] • K[PtCl5 (NH3)] • [Cu(en)(NH3)2][Co(en)Cl4] • [Pt(en)2Br2](ClO4)2
