Question

Which of the following ions have noble gas electron configurations?

a.${\mathbf{Fe}}^{\mathbf{2}\mathbf{+}}\mathbf{,}\mathbf{}{\mathbf{Fe}}^{\mathbf{3}\mathbf{+}}\mathbf{,}\mathbf{}{\mathbf{Sc}}^{\mathbf{3}\mathbf{+}}\mathbf{,}\mathbf{}{\mathbf{Co}}^{\mathbf{3}\mathbf{+}}$

b.${\mathbf{Tl}}^{\mathbf{+}}\mathbf{,}{\mathbf{Te}}^{\mathbf{2}\mathbf{-}}\mathbf{,}{\mathbf{Cr}}^{\mathbf{3}\mathbf{+}}$

c.${\mathbf{Pu}}^{\mathbf{4}\mathbf{+}}\mathbf{,}{\mathbf{Ce}}^{\mathbf{4}\mathbf{+}}\mathbf{,}{\mathbf{Ti}}^{\mathbf{4}\mathbf{+}}$

d.${\mathbf{Ba}}^{\mathbf{2}\mathbf{+}}\mathbf{,}{\mathbf{Pt}}^{\mathbf{2}\mathbf{+}}\mathbf{,}{\mathbf{Mn}}^{\mathbf{2}\mathbf{+}}$

Short answer

a.${\mathrm{Sc}}^{3+}+=\left[\mathrm{Ar}\right]$

b.$T{e}^{2-}=\left[\mathrm{Xe}\right]$

c.$C{e}^{4+}=\left[\mathrm{Xe}\right]\mathrm{and}{\mathrm{Ti}}^{4+}=\left[\mathrm{Ar}\right]$

d.${\mathrm{Ba}}^{2+}=\left[\mathrm{Xe}\right]$

Step-by-step solution

Describe the general electronic configuration of noble gases:

The general electronic configuration of noble gases is${\mathrm{ns}}^2,{\mathrm{np}}^6$.

The only exception is He which has $1{\mathrm{s}}^2$configuration.

Write the configuration of all the ions in part a and check if they’ve noble gas configuration:

$$\begin{gathered} {\mathrm{Fe}}^{2+}=\left[\mathrm{Ar}\right]3{\mathrm{d}}^6 \\ {\mathrm{Fe}}^{35}=\left[\mathrm{Ar}\right]3{\mathrm{d}}^5 \\ {\mathrm{Sc}}^{3+}=1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^6=\left[\mathrm{Ar}\right] \\ {\mathrm{Co}}^{3+}=\left[\mathrm{Ar}\right]3{\mathrm{d}}^6 \end{gathered}$$

We can clearly see that only ${\mathrm{Sc}}^{3+}$has noble gas configuration of $3{\mathrm{s}}^{2}3{\mathrm{p}}^6$i.e. Argon.

Proceed in a similar manner for every other part of the question:

In part (b),

$$\begin{gathered} {\mathrm{Tl}}^{+}=\left[\mathrm{Xe}\right]4{\mathrm{f}}^{14}5{\mathrm{d}}^{10}6{\mathrm{s}}^2 \\ {\mathrm{Cr}}^{3+}=\left[\mathrm{Ar}\right]3{\mathrm{d}}^3 \\ {\mathrm{Te}}^{2-}=\left[\mathrm{Kr}\right]4{\mathrm{d}}^{10}5{\mathrm{s}}^{2}5{\mathrm{p}}^6=\left[\mathrm{Xe}\right] \end{gathered}$$

Here only${\mathrm{Te}}^{2-}$ has noble gas configuration of Xenon.

In part (c),

$$\begin{gathered} {\mathrm{Pu}}^{4+}=\left[\mathrm{Rn}\right]5{\mathrm{f}}^4 \\ {\mathrm{Ti}}^{4+}=\left[\mathrm{Ne}\right]3{\mathrm{s}}^{2}3{\mathrm{p}}^6=\left[\mathrm{Ar}\right] \\ {\mathrm{Ce}}^{4+}=1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^{2}3{\mathrm{d}}^{10}4{\mathrm{p}}^{6}5{\mathrm{s}}^{2}4{\mathrm{d}}^{10}5{\mathrm{p}}^{6}6{\mathrm{s}}^{0}5{\mathrm{d}}^{0}4{\mathrm{f}}^0 \end{gathered}$$

Here both${\mathrm{Ti}}^{4+},{\mathrm{Ce}}^{4+}$have noble gas configurations.

Similarly for part (d),

$$\begin{gathered} {\mathrm{Ba}}^{2+}=\left[\mathrm{xe}\right]6{\mathrm{s}}^0=\left[\mathrm{xe}\right] \\ {\mathrm{Pt}}^2=\left[\mathrm{xe}\right]4{\mathrm{f}}^{14}5{\mathrm{d}}^8 \\ {\mathrm{Mn}}^{2+}=\left[\mathrm{Ar}\right]3{\mathrm{d}}^{5}4{\mathrm{s}}^0 \end{gathered}$$

Here we can see that only ${\mathrm{Ba}}^{2+}$has a noble gas configuration of Xenon,