Which of the following ions exhibits the highest magnetic moment?
(a) Fe²⁺
(b) Mn²⁺
(c) Cu²⁺
(d) Co²⁺
Answer (2)
Among the ions Fe²⁺, Mn²⁺, Cu²⁺, and Co²⁺, Mn²⁺ has the highest magnetic moment due to having 5 unpaired electrons, resulting in a magnetic moment of approximately 5.9 BM. In contrast, the other ions have lower magnetic moments due to fewer unpaired electrons. Therefore, the chosen option is (b) Mn²⁺.
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To determine which ion exhibits the highest magnetic moment, we need to consider the number of unpaired electrons in each ion. The magnetic moment is related to the spin of unpaired electrons and can be calculated using the formula:
μ = n ( n + 2 )
where:
μ is the magnetic moment,
n is the number of unpaired electrons.
Let's analyze each of the given ions:
Fe²⁺ (Iron ion):
Iron (Fe) has an atomic number of 26.
Its electronic configuration is [ A r ] 3 d 6 4 s 2 .
For Fe²⁺, two electrons are removed, which typically are the two 4s electrons, resulting in configuration [ A r ] 3 d 6 .
In the 3d subshell, there are 4 unpaired electrons.
Magnetic moment: μ = 4 ( 4 + 2 ) = 24 ≈ 4.90 B.M. (Bohr Magneton)
Mn²⁺ (Manganese ion):
Manganese (Mn) has an atomic number of 25.
Its electronic configuration is [ A r ] 3 d 5 4 s 2 .
For Mn²⁺, two electrons are removed, usually the 4s electrons, resulting in configuration [ A r ] 3 d 5 .
There are 5 unpaired electrons.
Magnetic moment: μ = 5 ( 5 + 2 ) = 35 ≈ 5.92 B.M.
Cu²⁺ (Copper ion):
Copper (Cu) has an atomic number of 29.
Its electronic configuration is [ A r ] 3 d 10 4 s 1 .
For Cu²⁺, two electrons are removed, resulting in configuration [ A r ] 3 d 9 .
There is 1 unpaired electron.
Magnetic moment: μ = 1 ( 1 + 2 ) = 3 ≈ 1.73 B.M.
Co²⁺ (Cobalt ion):
Cobalt (Co) has an atomic number of 27.
Its electronic configuration is [ A r ] 3 d 7 4 s 2 .
For Co²⁺, two electrons are removed, typically the 4s electrons, resulting in configuration [ A r ] 3 d 7 .
There are 3 unpaired electrons.
Magnetic moment: μ = 3 ( 3 + 2 ) = 15 ≈ 3.87 B.M.
Based on these calculations, Mn²⁺ has the highest magnetic moment due to having the most unpaired electrons (5) among all the ions listed.
Therefore, the correct choice is (b) Mn²⁺.
