Transition metals

the 44 chemical elements with the ordinal numbers from 21 to 30, 39 to 48 and 57 to 80 are usually called transition metals. This name is justified in its position in the periodic system, there itself there the transition by the successive increase of electrons into the D - atomicorbitally along each period shows. Transition elements are defined chemically as elements, which train at least an ion with partial D-bowl .

Examples of transition metals

scandium
gold
Group of 3 (III B) 4 (III B) 5 (III B) 6 (III B) 7 (III B) 8 (III B) 9 (III B) 10 (III B) 11 (III B) 12 (III B)
4. Period Sports club 21 Ti 22 V 23 CR 24 Mn 25 Fe 26 CO 27 never 28 cu 29 Zn 30
5. Period Y 39 Zr 40 Nb 41 Mo 42 Tc 43 Ru 44 RH 45 Pd 46 AG 47 CD 48
6. Period La 57 -

Lu 71

Hf 72 TA 73 W 74 RH 75 OS 76 IR 77 Pt 78 outer ones 79 Hg 80


table of contents

Elektronenkonfiguration

of main group elements, in the periodic system before the transition metals are not (thus the element number 1 to 20) have electrons in the D - orbitals, but only in the s - and p- Orbitals (although it is accepted that the empty D - plays orbital in the behavior of such elements such as silicon , phosphorus and sulfur a role).

With the D-block - elements from scandium to zinc, become the D - orbital along the period filled up. Except copper and chrome all have D - Block element two electrons in their outside s - orbital, even elements with incomplete 3d-Orbitalen. That is unusual: lower orbital before the outside bowls are normally filled up. The s - Orbital into the D - are block elements however in a lower energy state than the D - lower shells. ThereAtoms are anxious to take as low an energy state as possible the s - bowls are first filled up. The exceptions with chrome and copper - which only one electron in their outside orbital possess - are justified by electron repulsion. Dividing the electrons on s - and D - orbitalleads to lower energy conditions for the atoms than two electrons in the outside s - to platzieren orbital.

Not all D - Block elements are transition metals. Scandium and zinc do not fit into the definition indicated above. Scandium has an electron in its D - lower shell and 2 electrons in the outside s - Orbitally. There the only Scandiumion (sports club 3+) no electrons in the D - orbital has, can it naturally also no “partly filled” D - orbital to have. Something similar applies to zinc, there its only ion, Zn 2+, a completely filled D - orbital has.

Chemical characteristics

of transition elements are characterised generally by high tensile strength, density, melting points and boiling points . As other characteristics of the transition metals also these are on the ability of the electrons the D - to lead back orbital to be delokalisiert within the metal lattice. In metallic materials is it so that the characteristics are stronger all the, the are divided more electrons between the cores.

There are four typical characteristics of transition metals:

Oxidation conditions

compared with elements II. Group such as calcium gives it the ions of the transition elements in numerous oxidation conditions. Calcium ions do not lose usually any more than two electrons, whereas transition elements up to nine can deliver. If one regards the ionization enthalpies of both groups, one recognizes also thatReason for it. The energy, which is necessary for the distance of electrons of calcium, is low, as long as to one tries to remove electrons below its outside both s - orbital. Approx. 3+ have an ionization enthalpy, which is so high that it does not occur normally. Transition elements such as vanadiumon the other hand rather linear rising ionization enthalpies have orbital along their s - and D - because of the small energy difference between the 3d and 4s-Orbitalen. Transition elements occur therefore also with very high oxidation numbers.

Along one period can one certain behavior patterns recognize:

  • The number of oxidation conditions takes toto the manganese too and sinks then again. That is to be due to the stronger attraction of the protons in the core, whereby the delivery is made more difficult by electrons.
  • The elements in their low Oxidationsstufen normally occur as simple ions. In higher Oxidationsstufen are they usually kovalent onother electronegative elements such as oxygen or Fluor bind, often than anions.

Characteristics as a function of the oxidation condition:

  • Higher Oxidationsstufen become less stable along the period.
  • Ions in higher Oxidationsstufen are good oxidizing agents, whereas elements are in low Oxidationsstufen reducing agents.
  • (2+) - ions begin at the beginning thatPeriod as strong reducing agents and become then ever more stable.
  • (3+) - ions against it begin stably and become then ever better oxidizing agents.

catalytic activity

of transition metals are good homogeneous or heterogeneous catalysts, z. B. iron is the catalyst for the Haber-Bosch-process. Nickeland platinum for the hydrogenation by alkenes are used. Palladium (Pd) is taken gladly for the catalytic linkage of CC connections (Suzuki, tail, silence etc.). Rhodium (RH), iridium (IR) and ruthenium (Ru) become z. B. used in the asymmetischen hydrogenation of prochiraler molecules. Into mostCases phosphorus connections are used here as ligands for the Stereokontrolle. The most well-known ligands are z. B. BINAP of R. Noyori (Nobelpreis 2001), DIOP von Kagan, JosiPhos/WalPhos, and DuPhos. All ligands mentioned bidentat together it and chelatisierend are, speak two phosphorus atoms to possess, which howpliers to the transition metal “bind”.

colored connections

if the frequency of electromagnetic radiation changed, we notice ourselves different colors. They result from the different composition of light, after it was reflected, transmitted or absorbed to contact with a material- one speaks also of Remission. Because of their structure transition metals train many different colored ions and complexes. The colors differ even with the same element - MNO 4 (Mn in the Oxidationsstufe +7) is violet connection, Mn 2+ is howeverpale-pink.

Komplexbildung can play a substantial role during the colour. The ligands have a large influence on the 3d-Schale. They partly tighten the 3d-Elektronen and split them into higher and lower (regarding the energy) groups. Electromagnetic radiation is absorbed only iftheir frequency of the energy difference of two energy conditions of the atom corresponds (because of the formula E=hν.) if to light on an atom with split up 3d-Orbitalen meets, some electrons into the higher condition is raised. Compared to a nichtkomplexierten ion different frequencies can be absorbed, and therefore one can observe also different colors.

The color of a complex hangs off of:

  • the kind of the metal ion, exactly taken of the number of electrons in the D - orbitals
  • of the arrangement of the ligands around the Metallion (complex isomers can accept different colors)
  • of the kind of the ligands around thatMetallion. The stronger they ligands are, the more largely are the energy difference between the two split up 3 D - groups.

The complexes of the D-block-element zinc (strictly taken no transition element) are colorless, since the 3d-Orbitale is full and therefore also no electrons be raised can.

 

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