Spin Magnetic Moment (B.M.)

The spin magnetic moment is a measure of the magnetic behavior of a compound or an atom. It is represented in units of Bohr magnetons (B.M.) and is calculated based on the number of unpaired electrons in the compound or atom.

Structure of Hg[Co(SCN)4]

To determine the spin magnetic moment of the compound Hg[Co(SCN)4], we first need to understand its structure.

Hg[Co(SCN)4] is a coordination compound where mercury (Hg) acts as a cation and forms coordination bonds with four thiocyanate (SCN) anions. The central cobalt (Co) atom is coordinated to four thiocyanate ligands, forming a tetrahedral geometry.

Determining the Number of Unpaired Electrons

To calculate the spin magnetic moment of Hg[Co(SCN)4], we need to determine the number of unpaired electrons in the compound. This can be done by considering the electronic configuration of the central cobalt atom.

The atomic number of cobalt (Co) is 27. Its electronic configuration is [Ar] 3d^7 4s^2. In a tetrahedral complex, the d orbitals split into two sets of different energy levels - the lower energy set (t2g) and the higher energy set (eg).

Since there are four ligands in the coordination sphere, the d orbitals are split into t2g (dxy, dxz, and dyz) and eg (dx^2-y^2 and dz^2).

Calculating the Number of Unpaired Electrons

To determine the number of unpaired electrons, we need to fill the t2g and eg orbitals with electrons based on Hund's rule. Hund's rule states that electrons occupy separate orbitals with parallel spins before pairing up.

In the case of Hg[Co(SCN)4], the electronic configuration of cobalt is [Ar] 3d^7. Since there are three t2g orbitals, three electrons will occupy these orbitals with parallel spins. Therefore, there will be one unpaired electron in the eg set of orbitals.

Calculating the Spin Magnetic Moment

The spin magnetic moment can be calculated using the formula:

Spin Magnetic Moment (B.M.) = √n(n+2)

Where n is the number of unpaired electrons.

In the case of Hg[Co(SCN)4], there is one unpaired electron (n = 1). Plugging this value into the formula, we get:

Spin Magnetic Moment (B.M.) = √1(1+2) = √3

Rounding off to two decimal places, the spin magnetic moment of Hg[Co(SCN)4] is 3.87 B.M.

Summary

- The spin magnetic moment of a compound or atom is a measure of its magnetic behavior.
- Hg[Co(SCN)4] is a coordination compound with a tetrahedral geometry.
- The electronic configuration of cobalt in Hg[Co(SCN)4] is [Ar] 3d^7.
- Based on the electronic configuration, there is one unpaired electron in the eg set of orbitals.
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