Are the following ions diamagnetic or paramagnetic? C r + 3 , C a + 2 , N a + , C r , F e +

Truong-Son N.

Mar 29, 2016

Notice how $\text{Cr}$ is not an ion. :)

Anyways, we can start from the electron configuration of the neutral atoms. I'm assuming you meant ${\text{Cr}}^{3+}$, ${\text{Ca}}^{2+}$, and ${\text{Fe}}^{3+}$...

$\text{Cr}$: $\left[Ar\right]3d^{5}4s^1$

$\text{Ca}$: $\left[Ar\right]4s^2$

$\text{Na}$: $\left[Ne\right]3s^1$

$\text{Fe}$: $\left[Ar\right]3d^{6}4s^2$

The rightmost orbitals listed here are highest in energy, so we ionize these atoms by booting off the highest-energy electrons. Thus:

$\text{Cr}\to {\text{Cr}}^{3+}+3e^{-}$
$\left[Ar\right]3d^{5}4s^1\to \left[Ar\right]3d^3$

Since there are $5$ $3d$ orbitals, they are not all at least singly filled yet, and thus, all three electrons in the lowest-energy configuration are unpaired. So, this is paramagnetic.

The original atom is also paramagnetic. The $4s$ subshell contains $1$ electron (in one $4s$ orbital) and the $3d$ subshell contains $5$ electrons, one in each $3d$ orbital. No valence electrons are paired here.

That's in agreement with our expectations from Hund's Rule (generally, for the lowest-energy configuration, maximize parallel spins where possible by singly-filling all orbitals of very similar energies first and then doubling up afterwards).

$\text{Ca}\to {\text{Ca}}^{2+}+2e^{-}$
$\left[Ar\right]4s^2\to \left[Ar\right]\Rightarrow 1s^{2}2s^{2}2p^{6}3s^{2}3p^6$

This is a noble gas configuration, so no electrons are unpaired Thus, this is diamagnetic.

$\text{Na}\to {\text{Na}}^{+}+e^{-}$
$\left[Ne\right]3s^1\to \left[Ne\right]\Rightarrow 1s^{2}2s^{2}2p^6$

This is a noble gas configuration, so no electrons are unpaired. Thus, this is diamagnetic.

$\text{Fe}\to {\text{Fe}}^{3+}+3e^{-}$
$\left[Ar\right]3d^{6}4s^2\to \left[Ar\right]3d^5$

Since there are $5$ $3d$ orbitals, in accordance with Hund's Rule, all five electrons in the lowest-energy configuration are unpaired. So, this is paramagnetic.

Reference: https://socratic.org/questions/are-the-following-ions-diamagnetic-or-paramagnetic-cr-3-ca-2-na-cr-fe-3