I am having problems with this lab please read the attached and then i you could

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I am having problems with this lab please read the attached and then i you could help with the complex ion formed in the following question

EXPERIMENT 10: THE COLORS OF COORDINATION CHEMISTRY Introduction One interesting way in which transition metals differ from main group metals is their ability to form coordination compounds. Coordination compounds are formed between a metal atom or ion and a molecule with one or more unshared electron pairs, called a ligand Ligands may be classified according to the number of donor atoms they contain . A monodentute ligand donates a single electron pair to the metal or metal ion Common examples include NH,, H:O, NO. CN A bidentate ligand, as the name suggests, donates two electron pairs to the metal or metal ion. A good example is ethylenediamine, NH CH:CH:NHs Anions as well as neutral molecules may act as ligands. If one or more neutral molecules coordinate to a metal ion, the resulting species retains the charge of the transition metal ion and is called a complex ion. For example, most transition metals form complex ions with water molecules when in aqueous solution. Examples include [Col H2O)and [Ni(H20MP. If one or more anions coordinate to a metal ion, a complex ion with an overall negative charge may result. Examples include [Co(NO )] and [Fe(CNJ When writing formulas for complex ions and coordination compounds, the molecules inside the brackets represent ligands physically attached, or coordinated, to the metal ion. Anything outside of the brackets is present for charge balance. Therefore, the formulas [Co(H O).]Cl, and [Ni(H:O ]Ch represent neutral compounds in which the chloride ions are present for charge balance. The formulas K [Co(NO:%] and K.[Fe(CN) ] represent molecules containing negatively charged complex ions with potassium cations present for charge balance. Most transition metal ions form complex ions with water molecules when in aqueous solution. Such compounds readily form because water is present in excess. However, water is not a particularly strong ligand. Such compounds are prone to substitution reactions in which the water molecules are successively replaced with other ligands. Such reactions are often accompanied by a change in the color of the solution. For example, the green [Nial,0)"ion is formed when many nickel(11) salts are dissolved in water. Upon the addition of concentrated NH3 however, the color changes to blue as [Ni(NH)612. is formed. green blue Where Does the Color Come From? One of the most striking aspects of transition metal chemistry is the formation of brightly colored solutions. The colors of such complexes can be explained by a simple model known as crystal field theory. The basic premise of crystal field theory is that complex ions form because of the attractions between the electrons on the ligand and the positive charge on the metal ion. However, the electrons on the ligand also repel the electrons in the metal d orbitals. In the absence of ligands, electrons in the d orbitals all have the same energy, they are degenerate 118

Explanation / Answer

chromium complexes

[Cr(H2O)6]3+ is responisble for imparting violet color

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