1. Explain why halide ions (e.g., F? , Cl? , Br? , I? ) function only as monoden

Question

1. Explain why halide ions (e.g., F? , Cl? , Br? , I? ) function only as monodentate ligands in coordination compounds even though halide ions contain four unshared pairs of electrons.

2. Some old weather forecasting devices utilized the following reaction, [Co(OH2)6] 2+(aq, pink) + 4Cl? (aq, colorless) ? [CoCl4] 2? (aq, dark blue) + 6H2O(l, colorless) These devices were used to predict rain - if the device showed a pink color, then rain was imminent; if the device showed a blue color, then rain was not in the forecast. Draw the crystal field splitting diagrams for both [Co(OH2)6] 2+ and [CoCl4] 2? using the following information and explain why [Co(OH2)6] 2+ is pink while [CoCl4] 2? ,is dark blue. ? H2O is a strong-field ligand ? Cl? is a weak-field ligand ? [Co(OH2)6] 2+ has an octahedral structure whereas [CoCl4] 2- has a tetrahedral structure

3. Use crystal field splitting diagrams to explain why Ni(NH3)6 2+ is paramagnetic while Ni(CN)6 4? is diamagnetic. How many unpaired electrons exist in each ion?

4. Are all the exothermic reactions spontaneous? Are all the endothermic reactions nonspontaneous? Explain your reasoning using appropriate equations.

Explanation / Answer

1)

Monodentate ligands have only one atom capable of binding to a central metal atom or ion and the ligand which binds to the central metal atom through two donor is called bidentate ligand. Here, the chloride has four lone pair of electrons but it can donate one lone pair for the bonding to the central metal atom through only one atom. So, it is monodentate ligand. Similarly, halides are the monodentate ligand so it can bond to the central atom through only one donor atom. Therefore, halide ions (e.g., F- , Cl- , Br- , I- ) function only as monodentate ligands in coordination compounds even though halide ions contain four unshared pairs of electrons.

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