Complex ions?

Question

Why does transition metals form coloured complexed ions?

Answer 1

Since light is absorbed and emmitted by the valance electrons of atoms, transition metals, and other metals, have nummerous electrons in the d orbital range that is just at the right quantum for absorbing and emmitting light in the visible spectrum. Transition metals are visible anyway, but when complexed it alters the emmission spectrum and thus you get pretty colors.

Answer 2

Transition metals have electrons in the d orbital; there are 5 d orbitals and they can hold a total of 18 electrons. The transition elements have valence electrons in two shells instead of only one. This structure gives them their outstanding ability to form ions containing more than one atom (complex ions, or coordination compounds), with a central atom or ion (often of a transition metal) surrounded by ligands in a regular arrangement. Theories on the bonding in these ions are still being refined. The elements in the periodic table from scandium to copper (atomic numbers 21–29), yttrium to silver (39–47), and lanthanum to gold (57–79, including the lanthanide series) are frequently designated the three main transition series. (Those in the actinide series and beyond, 89–111, also qualify.) All are metals, many of major economic or industrial importance (e.g., iron, gold, nickel, titanium). Most are dense, hard, and brittle, conduct heat and electricity well, have high melting points, and form alloys with each other and other metals. Their electronic structure lets them form compounds at various valences. Many of these compounds are coloured and paramagnetic (see paramagnetism) and (as do the metals themselves) often act as catalysts. See also rare earth metal. The colors come from the energy levels of the various electrons.

Answer 3

Transition metals are characterized by having partially filled d-orbitals. In an isolated transition metal atom or ion, the energies of these orbitals are all equal.

There are two common approaches to describing what happens when a transition metal ion in solution is coordinated by other ions or ligands, forming a coordination complex. These approaches are called "crystal field theory", and "ligand field theory". In crystal field theory, one thinks of the ions or ligands surrounding the metal ion as creating an electrostatic field that removes the energy degeneracy of the metal ion's d-orbitals (i.e., the d-orbitals acquire different energies depending on their spatial orientation with respect to the positions of the ligands). In the ground state, the metal's electrons populate the lower-energy d-orbitals, leaving the higher-energy orbitals unoccupied. It turns out that for many metal-ligand systems, the difference in energy between the d-orbitals in the electrostatic field corresponds to the energy of photons of visible light, and valence electrons can be excited from a lower-energy d-orbital to a higher-energy d-orbital by the absorption of a photon with the appropriate energy (or wavelength, because the energy of a photon is inversely proportional to its wavelength: E = h*c/wavelength). This absorption gives rise to the colors of transition metal complexes.

Ligand field theory is similar, but instead of simply assuming that the coordinating ions/ligands create an electrostatic field that the metal ion "responds" to, one creates new molecular orbitals by combining the d-orbitals (and possibly other orbitals that have similar energies) of the metal ion with appropriate orbitals of the ions/ligands. This again splits the energy degeneracy of the d-orbitals of the metal ion, and the resulting energy differences allow for the absorption of a visible light photon and the excitation of a valence electron.

See sources.

Answer 4

d-d electron transitions, which have energies which correspond to the wavelengths of visible light.

And the d orbitals can hold 10 electrons, not 18.