Chapter 2, Problem 140AE

Interpretation Introduction

Interpretation:

The elements having the ground-state electronic configurations different from what we would expect from their positions in the periodic table are to be listed.

Concept Introduction:

The distribution of the electrons present in an atom in the respective atomic orbitals is known as the electronic configuration. However, some elements have different ground-state configurations than expected from their placement in the periodic table.

To determine: The elements having different ground-state configurations than expected from their placement in the periodic table.

Answer to Problem 140AE

Answer

The elements $\text{Cr},\text{Cu},\text{Nb},\text{Mo},\text{Tc},\text{Ru},\text{Rh},\text{Pd},\text{Ag},\text{Pt},\text{Au}\text{and}\text{Rg}$ exhibit electronic configurations different from their expected ones.

Explanation of Solution

The filling of orbitals according to their energy levels gives the expected ground-state electronic configurations for the elements. And the following elements exhibit ground-state configurations that are different from what was expected with respect to their placement in the periodic table.

In the case of Chromium and copper, the expected configuration in accordance to the Aufbau principle would be,

$\begin{array}{l}\text{Cr}=\left(1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^{6}3{\text{s}}^{2}3{\text{p}}^{6}4{\text{s}}^{2}3{\text{d}}^4\right)\\ \text{Cu}=\left(1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^{6}3{\text{s}}^{2}3{\text{p}}^{6}4{\text{s}}^{2}3{\text{d}}^9\right)\end{array}$

But the actual configuration it exhibits is,

$\begin{array}{l}\text{Cr}=\left(1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^{6}3{\text{s}}^{2}3{\text{p}}^{6}4{\text{s}}^{1}3{\text{d}}^5\right)\\ \text{Cu}=\left(1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^{6}3{\text{s}}^{2}3{\text{p}}^{6}4{\text{s}}^{1}3{\text{d}}^{10}\right)\end{array}$

This happens as completely filled sub levels are more stable than the partly filled ones. Also, a half filled sub level is more stable than the partly filled one.

In the case of Niobium, the expected configuration in accordance to the Aufbau principle would be,

$\text{Nb}=\left(1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^{6}3{\text{s}}^{2}3{\text{p}}^{6}3{\text{d}}^{10}4{\text{s}}^{2}4{\text{p}}^{6}5{\text{s}}^{2}4{\text{d}}^3\right)$

But the actual configuration it exhibits is,

$\text{Nb}=\left(1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^{6}3{\text{s}}^{2}3{\text{p}}^{6}3{\text{d}}^{10}4{\text{s}}^{2}4{\text{p}}^{6}5{\text{s}}^{1}4{\text{d}}^4\right)$

The repulsion of two electrons within the same orbital pushes one electron from the $5\text{s}$ to the $4\text{d}$ orbital.

Some other elements that exhibit electronic configurations different from expected ones are,

$\begin{array}{l}\text{Mo}=\left(\text{Molybdenum}\right)\left(1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^{6}3{\text{s}}^{2}3{\text{p}}^{6}3{\text{d}}^{10}4{\text{s}}^{2}4{\text{p}}^{6}4{\text{d}}^{5}5{\text{s}}^1\right)\\ \text{Tc}=\left(\text{Technitium}\right)\left(1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^{6}3{\text{s}}^{2}3{\text{p}}^{6}3{\text{d}}^{10}4{\text{s}}^{2}4{\text{p}}^{6}4{\text{d}}^{5}5{\text{s}}^2\right)\\ \text{Ru}=\left(\text{Ruthenium}\right)\left(1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^{6}3{\text{s}}^{2}3{\text{p}}^{6}3{\text{d}}^{10}4{\text{s}}^{2}4{\text{p}}^{6}4{\text{d}}^{7}5{\text{s}}^1\right)\\ \text{Rh}=\left(\text{Rhodium}\right)\left(1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^{6}3{\text{s}}^{2}3{\text{p}}^{6}3{\text{d}}^{10}4{\text{s}}^{2}4{\text{p}}^{6}4{\text{d}}^{8}5{\text{s}}^1\right)\\ \text{Pd}=\text{(Palladium)}\left(1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^{6}3{\text{s}}^{2}3{\text{p}}^{6}3{\text{d}}^{10}4{\text{s}}^{2}4{\text{p}}^{6}4{\text{d}}^{10}\right)\\ \text{Ag}=\left(\text{Silver}\right)\left(1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^{6}3{\text{s}}^{2}3{\text{p}}^{6}3{\text{d}}^{10}4{\text{s}}^{2}4{\text{p}}^{6}4{\text{d}}^{10}5{\text{s}}^1\right)\\ \text{Pt}=\text{(}\left(\text{Platinum}\right)\left(1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^{6}3{\text{s}}^{2}3{\text{p}}^{6}3{\text{d}}^{10}4{\text{s}}^{2}4{\text{p}}^{6}4{\text{d}}^{10}5{\text{s}}^{2}5{\text{p}}^{6}4{\text{f}}^{14}{\text{5d}}^9{\text{6s}}^1\right)\\ \text{Au}=\left(\text{Gold}\right)\left(1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^{6}3{\text{s}}^{2}3{\text{p}}^{6}3{\text{d}}^{10}4{\text{s}}^{2}4{\text{p}}^{6}4{\text{d}}^{10}5{\text{s}}^{2}5{\text{p}}^{6}4{\text{f}}^{14}{\text{5d}}^{10}{\text{6s}}^1\right)\\ \text{Rg}=\left(\text{Roentgenium}\right)\left(1{\text{s}}^{2}2{\text{s}}^{2}2{\text{p}}^{6}3{\text{s}}^{2}3{\text{p}}^{6}3{\text{d}}^{10}4{\text{s}}^{2}4{\text{p}}^{6}4{\text{d}}^{10}5{\text{s}}^{2}5{\text{p}}^{6}4{\text{f}}^{14}5{\text{d}}^{10}6{\text{s}}^{2}6{\text{p}}^{6}5{\text{f}}^{14}6{\text{d}}^{9}7{\text{s}}^2\right)\end{array}$

The compounds that portray the ${\text{d}}^{10}$ systems do so in order to attain extra stability. In case of the $\text{Ru}\text{and}\text{Rh}$, such configurations are attained by these compounds in order to attain extra stability by attaining a completely filled ${\text{T}}_{\text{2}}\text{g}$ orbitals.

Conclusion

The elements having the ground-state electronic configurations different from what we would expect from their positions in the periodic table are $\text{Cr},\text{Cu},\text{Nb},\text{Mo},\text{Tc},\text{Ru},\text{Rh},\text{Pd},\text{Ag},\text{Pt},\text{Au}\text{and}\text{Rg}$.