Transition Metal Colors in Aqueous Solution

Transition Metal Colors in Aqueous Solution The transition metals form colored ions, complexes, and compounds in aqueous solution. The characteristic colors are helpful when performing a qualitative analysis to identify the composition of a sample. The colors also reflect interesting chemistry that occurs in transition metals. Transition Metals and Colored Complexes A transition metal is one that forms stable ions that have incompletely filled d orbitals. By this definition, technically not all of the d block elements of the periodic table are transition metals. For example, zinc and scandium arent transition metals by this definition because Zn2 has a full d level, while Sc3 has no d electrons. A typical transition metal has more than one possible oxidation state because it has a partially filled d orbital. When transition metals bond to one more neutral or negatively charged nonmetal species (ligands), they form what are called transition metal complexes. Another way to look at a complex ion is as a chemical species with a metal ion at the center and other ions or molecules surrounding it. The ligand attaches to the central ion by dative covalent or coordinate bond. Examples of common ligands include water, chloride ions, and ammonia. Energy Gap When a complex forms, the shape of the d orbital changes because some are nearer the ligand than others: Some d orbitals move into a higher energy state than before, while others move to a lower energy state. This forms an energy gap. Electrons can absorb a photon of light and move from a lower energy state into a higher state. The wavelength of the photon that is absorbed depends on the size of the energy gap. (This is why splitting of s and p orbitals, while it occurs, does not produce colored complexes. Those gaps would absorb ultraviolet light and not affect the color in the visible spectrum.) Unabsorbed wavelengths of light pass through a complex. Some light is also reflected back from a molecule. The combination of absorption, reflection, and transmission results in the apparent colors of the complexes. Transition Metals May have More Than One Color Different elements may produce different colors from each other. Also, different charges of one transition metal can result in different colors. Another factor is the chemical composition of the ligand. The same charge on a metal ion may produce a different color depending on the ligand it binds. Color of Transition Metal Ions in Aqueous Solution The colors of a transition metal ion depend on its conditions in a chemical solution, but some colors are good to know (especially if youre taking AP Chemistry): Transition Metal Ion Color Co2+ pink Cu2+ blue-green Fe2+ olive green Ni2+ bright green Fe3+ brown to yellow CrO42- orange Cr2O72- yellow Ti3+ purple Cr3+ violet Mn2+ pale pink Zn2+ colorless A related phenomenon is the emission spectra of transition metal salts, used to identify them  in  the  flame test.

Problems with Included Tree Bark

Problems with Included Tree Bark Included bark or ingrown bark tissues often develop where two or more stems grow closely together causing weak, under-supported branch angles. Bark often grows around the branching stem attachment and into the union between the two stems. Bark has no strong supportive fiber strength as wood does so the connection is much weaker than a union without included bark. Pruning All maturing trees are subject to having bark inclusions and need pruning while limbs are smaller and easier to remove. Any signs of a cracked weak branch angle (shaped like a V) with included bark that occurs on the main stem or any included bark areas on larger, lower limbs should be considered a defect. Connected stems with a supported U or Y shape are desirable.  Proper pruning will help prevent included bark and encourage the proper shape. Dont Automatically Worry about Decay The presence of decay by itself does not make the tree a hazard tree. All trees have some rot and decay with advancing age. Decay is a problem where the wood is soft and hollowed out along with the presence of mushrooms/conks. Take immediate action if advanced decay is present or associated with weak branches or included bark. Signs for Concern   A weak branch union occurs on the main stem.A weak branch union is associated with a crack, cavity, or another defect.