The Transition Elements and Their Coordination Compoundsj Color and Magnetism of Compounds ¢â‚¬¢ Most

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    The Transition Elements and Their Coordination Compounds Cu: plumbing Fe: in steel Cr: in automobile parts Au, Ag: jewelry W: light bulb filament Ti: bicycle Pt: auto catalytic converters Zr: nuclear-reactor liners Nitrinol (Ni and Ti used in stents) And many more Transition elements make up the d orbitals (we will cover here) Inner transition metals make up the d and f orbitals The transition elements (d block) and inner transition elements (f block) in the periodic table

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    Example Writing Electron Configurations of Transition Metal Atoms and Ions Write condensed electron configurations for the following: (a) Zr; (b) V3+ (c) Mo3+. (Assume that elements in higher periods behave like those in Period 4.) Note that the general configuration is [noble gas] ns2(n - 1)dx. Recall that in ions the ns electrons are lost first. (a) Zr is the second element in the 4d series: [Kr] 5s24d2. (b) V is the third element in the 3d series: [Ar] 4s23d3. In forming V3+, three electrons are lost (two 4s and one 3d), so V3+ is a d2 ion: [Ar] 3d2 (c) Mo lies below Cr in Group 6B(6), so we expect the same exception as for Cr. Thus, Mo is [Kr] 5s14d5. In forming the ion, Mo loses the one 5s and two of the 4d electrons, so Mo3+ is a d3 ion: [Kr] 4d3

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    Horizontal trends in key atomic properties of the Period 4 elements

    • Atomic size decreases overall across a period. The d electrons fill inner orbitals, so they shield outer electrons from the increasing nuclear charge very efficiently and the outer 4s electrons are not pulled closer.

    • Electronegativity usually increases across a period but the transition metals exhibit a relatively small change in electronegativity. Metal in higher oxidation state is more positive has stronger pull on electron is more electronegative

    • IE1 increase relatively little because the inner 3d electrons shield efficiently and the outer 4s electron experiences only a slightly higher effective nuclear charge.

    Vertical trends in key properties within the transition elements

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    Trends Within a Group (relative to main-group elements) Atomic Size Increases as expected, from Period 4 to 5. No increase from Period 5 to 6 Lanthanides with buried “4f” sublevel orbitals appear between the 4d (period 5) and 5d (period 6) series An element in Period 6 is separated from the one above it in Period 5 by 32 electrons (ten 4d, six 5p, two 6s, and fourteen 4f). The extra shrinking that results from the increased nuclear charge due to the addition of the fourteen 4f electrons is called the: “Lanthanide Contraction” Order of Sublevel Orbital Filling Electronegativity (EN) – Relative ability of an atom in a covalent bond to attract shared electrons. EN of main-group elements decreases down group Greater size means less attraction by nucleus Greater Reactivity EN in transition elements is opposite the trend in main-group elements EN increases from period 4 to period 5.

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    No change from period 5 to period 6, since the change in volume is small and Zeff increases (f orbital electrons). Transition metals exhibit more covalent bonding and attract electrons more strongly than main-group metals The EN values in the heavy metals exceed those of most metalloids, forming salt-like compounds, such as CsAu and the Au- ion Ionization Energy Main-group elements increase in size down a group, decreasing the 1st ionization energy, making it relatively easier to remove the outer electrons The relatively small increase in size of transition metals, combined with the relatively large increase in nuclear charge (Zeff), results in a general increase in the first ionization energy down a group Density Atomic size (volume) is inversely related to density Across a period densities increase In transition metals the density down a group increases dramatically because atomic volumes change little from Period 5 to Period 6 while nuclear mass increases significantly Period 6 series contains some of the densest elements known: Tungsten, Rhenium, Osmium, Iridium, Platinum, Gold (Density 20 times greater than water, 2 times more dense than lead) Oxidation States

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    Colors of representative compounds of the Period 4 transition metals.

    titanium oxide

    sodium chromate

    potassium ferricyanide

    nickel(II) nitrate hexahydrate

    zinc sulfate heptahydrate

    scandium oxide

    vanadyl sulfate dihydrate

    manganese(II) chloride

    tetrahydrate cobalt(II) chloride

    hexahydrate

    copper(II) sulfate

    pentahydrate

    • Exhibit more than one • Ionic bonding is more prevalent for the lower oxidation states and covalent

    bonding is more prevalent for the higher oxidation states. At room temperature TiCl2 is an ionic solid and TiCl4 is a molecular liquid

    • In high oxidation states atoms have higher charge densities ⇒ polarize electron clouds of non-metals ⇒ covalent bonding

    • The oxides become less basic as the oxidation state increases TiO is a weak base in water and TiO2 is amphoteric.

    Color and Magnetism of Compounds

    • Most main group ionic compounds are colorless because the metal ion has a filled outer level;

    On the contrary, • Electrons in particular filled d-sublevels can absorb visible wavelengths and

    move to slightly higher energy d-orbitals. Therefore, many transition metal compounds have striking colors. Exceptions occur when d orbitals are empty or filled. Zn2+: [Ar] 3d10 and Sc3+ or Ti4+ [Ar] 3d0

    Formation of Coordination Compounds These are species consisting of a central metal cation (transition metal or main group metal) that is bonded to molecules and or anions called ligands. In order to maintain neutrality in the coordination compound, the complex ion is typically associated with other ions, called counterions. Therefore,

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    Metals ions are Lewis acids, because they accept electrons from Lewis bases. When metal cations combine with Lewis bases, the resulting species is called a complex ion, and the base is called a ligand. Ammonia is the Lewis base (electron donor). H+ and BF3 are Lewis acids (electron acceptors). Similarly, transition metals and their cations are Lewis acids. They have vacant orbitals that can accept electron pairs from donor atoms (Lewis bases) forming coordination compounds or complexes. Some examples are shown in the following table. Lewis Acid Lewis Base Complex Dissociation Constants Cr+3 + 6H2O → [Cr(OH2)6]+3 -- Co+3 + 6NH3 → [Co(NH3)6]+3 2.2 × 10-34 Ni+2 + 4CN- → [Ni(CN)4]-2 1.0 × 10-31 Fe + 5CO → [Fe(CO)5] -- Ag+ + 2NH3 → [Ag(NH3)2]+ 6.3 × 10-8 Lewis bases (anions or molecules) bonded to the central Lewis acid are called ligands (Latin = tie or bind). Charged coordination complexes also have counter ions associated with them to satisfy electroneutrality. For example, in [Ag(NH3)2]+NO3-, a nitrate anion is the counter ion. Counter ions are ionically bonded. When dissolved in water, the NO3- ion separates from the complex, but the two NH3 ligands remain firmly bound to the Ag+ ion by covalent bonds.

    H+ Hydrogen ion has a vacant 1s orbital. Nitrogen has a full sp 3 orbital. A co-ordinate covalent bond is formed when nitrogen donates its lone e - pair to hydrogen's empty 1s orbital.

    ammonia ammonium ion

    N

    H

    H H

    : + H+ N

    H

    H H

    H

    +

    N

    sp3 orbitals

    1s0

    H H H 1s11s11s1

    ammonia

    N

    H

    H H

    : + B

    F

    F

    F

    N

    H

    H H

    B

    F

    F

    F

    Boron has a vacant 2pz orbital. Nitrogen has a full sp 3 orbital. A co-ordinate covalent bond is formed when nitrogen donates its lone e - pair to boron's empty 2pz orbital.

    N

    sp3 orbitals

    sp2 orbitals 2pz

    B

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    Components of a Coordination Compound

    When solid complex dissolves in water, the complex ion and the counter ions separate, but ligands remain bound to central atom Coordination Numbers, Geometries, and Ligands Coordination Number (CN) - the number of ligand atoms that are bonded directly to the central metal ion. The coordination number is specific for a given metal ion in a particular oxidation state and compound (6 is the most common, 2 and 4 are often used.) Geometry - the geometry (shape) of a complex ion depends on the coordination number and nature of the metal ion. – See table below

    Donor atoms per ligand - molecules and/or anions with one or more donor atoms that each donate a lone pair of electrons to the metal ion to form a covalent bond. Importance of Coordination Complexes: Many biologically important substances are 'd'-transition metal coordination compounds that are made up of large organic molecules bound to the metal via coordinate covalent bonds, e.g.,

    hemoglobin (blood protein) is a coordination complex involving Fe. vitamin B-12 is a cobalt complex (cyanocobalamin) phthalocyaine blue is a Cu complex dye used for blue jeans and ink complexing agents are used