Question

What noble gas has the same electron configuration as each of the ions in the following compounds?

a. cesium sulfide

b. strontium fluoride

c. calcium nitride

d. aluminium bromide

Short answer

a. Xenon and Argon

b. Argon and Neon

c. Krypton and Neon

d. Neon and Krypton

Step-by-step solution

Write down the electronic configuration of cs+and S2for part a and compare them with the noble gases:

Cesium sulfide $\left(\mathrm{CsS}\right)=2{\mathrm{cs}}^{+}andS$

$Cs=1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{1}04s^{2}4p^{6}4d^{1}05s^{2}5p^{6}6s^1=\left[Xe\right]6s^1$

$\therefore C{s}^{+}=\left[Xe\right]$

$S=1s^{2}2s^{2}2p^{6}3s^{2}3p^4=\left[Ne\right]3s^{2}3p^4$

$S=1s^{2}2s^{2}2p^{6}3s^{2}3p^4=\left[Ne\right]3s^{2}3p^6=\left[Ar\right]$

For part b, write the formula and electron configuration of Sr2+and F- and compare them with noble gases:

Strontium fluoride $\left(Sr{F}_2\right)=S{r}^{2+}and2F^{-}$

$Sr=\left[Kr\right]5s^2$

$\therefore S{r}^{2+}=\left[kr\right]$

=$\left[Ne\right]$

For part c, write the formula of calcium nitride and electron configuration of both ions to compare them with noble gases:

Calcium Nitride $\left(C{a}_3{N}_2\right)=3C{a}^{(2+)}and2N^{\left(3-\right)}$

localid="1656924239459" $$\begin{gathered} Ca=\left[Ar\right]4S^2 \\ \therefore C{a}^{2+}=\left[Ar\right] \\ N=\left[He\right]2s^{2}2p^3 \\ \therefore N^{3-}=\left[He\right]2s^{2}2p^6=\left[Ne\right] \end{gathered}$$

Proceed similarly for part d:

Aluminium Bromide $\left(AlB{r}_3\right)=A{l}^{3+}and3B{r}^{-}$

role="math" localid="1656693099204" $\mathrm{Al}=\left[\mathrm{Ne}\right]{3\mathrm{s}}^{2}3p^1$

role="math" localid="1656693449818" $\therefore A{l}^{3+}=\left[Ne\right]$

$Br=\left[Ar\right]4s^{2}3d^{10}4p^5$

$\therefore B{r}^{-}=\left[Ar\right]4s^{2}3d^{10}4p^6=\left[Kr\right]$