The solid anhydrous solid CoCl2 is blue in color. Because it readily absorbs water from the air,

step 1 The solid and hydris COCL absorbs water from the air to form an octahedral aqua complex called o

The solid anhydrous solid CoCl2 is blue in color. Because it...

The solid anhydrous solid $\mathrm{CoCl}_{2}$ is blue in color. Because it readily absorbs water from the air, it is used as a humidity indicator to monitor if equipment (such as a cell phone) has been exposed to excessive levels of moisture. Predict what product is formed by this reaction, and how many unpaired electrons this complex will have.

Key Concepts

Electronic Configuration of Transition Metal Ions

This concept involves determining the distribution of electrons in the d-orbitals of a transition metal ion after accounting for ionization and the effects of ligand field splitting. By considering the d electron count, along with whether the complex is high spin or low spin (a result of ligand strength), one can predict the number of unpaired electrons, which is critical for understanding the magnetic and spectroscopic properties of the complex.

Ligand Field Theory

Ligand field theory explains how the approach of ligands alters the energy of the d-orbitals in a transition metal ion. In an octahedral field, the d-orbitals split into two groups with different energies. The magnitude of this splitting influences whether electrons will pair up in the lower-energy orbitals or occupy higher-energy ones, thereby determining both the color of the complex and the number of unpaired electrons.

Hydration Reaction

A hydration reaction is when water molecules interact with a compound, often a salt, leading to the formation of a hydrated complex. In the case of many transition metal salts, the anhydrous form can absorb water from the environment, with water molecules acting as ligands to the central metal ion, thereby altering physical and chemical properties.

Coordination Complex

This concept involves a central metal ion bonded to surrounding molecules or ions called ligands. The ligands donate lone pairs to the metal, forming coordinate covalent bonds. In many cases, such complexes display properties, such as color and magnetism, that differ markedly from those of the free metal ion.

Octahedral Geometry

Octahedral geometry is a common arrangement in coordination complexes where six ligands symmetrically surround the central metal ion. This geometry plays a crucial role in determining the splitting pattern of the metal d-orbitals, which in turn affects the electronic configuration, energy levels, and properties such as color and magnetism of the complex.

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