Electron configuration anomalous

The electron configurations of certain elements appear to violate the rules we have just discussed. For example, Figme 6.31 shows that the electron configuration of chromium (element 24) is [Ar]3d 4s rather than the [Ar]3d 4s configuration we might expect. Similarly, the configuration of copper (element 29) is [Ar]3d 4s instead of [Ar]3d 4s.  

atomic number 5, occurs naturally as two isotopes, and B, with natural abundances of 19.9% and 80.1%, respectively, (a) In what ways do the two isotopes differ from each other Does the electronic configuration of differ from that of B (b) Draw the orbital diagram for an atom of B. Which electrons are the valence electrons (c) Indicate three major ways in which the Is electrons in boron differ from its 2s electrons, (d) Elemental boron reacts with fluorine to form BF3, a gas. Write a balanced chemical equation for the reaction of solid boron with fluorine gas. (e) AHf for Bp3(g) is —1135.6 kl/mol Calculate the standard enthalpy change in the reaction of boron with fluorine, (f) When BCI3, also a gas at room temperature, comes into contact with water, the two react to form hydrochloric acid and boric add, H3BO3, a very weak acid in water. Write a balanced net ionic equation for this reaction. 

The valence electrons are the ones in the outermost occupied shell, the 2s and 2p electrons. The Is electrons constitute the core electrons, which we represent as [He] when we write the condensed electron configuration, [He]2s 2p . 

H3BO3 is a very weak acid, its chemical formula is written in molecular form, as discussed in Section 4.3. 

SECTION 6.3 Dispersion of radiation into its component wavelengths produces a specinan. If the spectrum contains all wavelengths, it is called a conlinuoiis spectrum if it contains only certain specific wavelengths, the spectrum is called a Bne spectrum. The radiation emitted hy excited hydrogen atoms forms a line spectrum. 

atomic number 5, occurs naturally as two isotopes, and B, with natural abundances of 

The two isotopes of boron differ in the number of neutrons in the nucleus, aoo (Sections 2.3 and 2.4) Each of the isotopes contains five protons, but °B contains five neutrons, whereas B contains six neutrons. The two isotopes of boron have identical electron configurations, ls 2s 2p, because each has five electrons. 

The Is and 2s orbitals are both spherical, but they differ in three important respects First, the Is orbital is lower in energy than the 

---

FIGURE 4. Medium-long form table showing highest and most common oxidation states of the d-block elements. Only two of these 30 ions, Ag+1 and Au+3, (shown in bold-face) show anomalous electronic configurations with respect to other ions in the same groups. 

Table B.l summarizes the ground-state electron configuration and formal APH indices (turn number t, angular number l-n) for each known element, together with atomic number (Z) and relative atomic mass). As shown by the asterisks in the Anal column, 20 elements exhibit anomalous electron configurations (including two that are doubly anomalous - Pd and Th), compared with idealized t/l-n APH descriptors. These are particularly concentrated in the first d-block series, as well as among the early actinides. Such anomalies are indicative of configurational near-degeneracies that may require sophisticated multi-reference approximation methods for accurate description.

The anomalous electronic configuration of chromium and copper is interpreted as the displacement of 1 electron from an r orbital into a d orbital these 2 elements have only 1 electron in the As subshell because the second electron was promoted into a id subshell. This example warns you that there are exceptions to the general pattern of electronic configurations of... 

Most of the anomalous electron configurations shown in Figure 5.17 occur in elements with atomic numbers greater than Z = 40, where the energy differences between subshells are small. In all cases, the transfer of an electron from one subshell to another lowers the total energy of the atom because of a decrease in electron-electron repulsions. 

FIGURE 5.17 The filling of shells and the structure of the periodic table. Only the "anomalous" electron configurations are shown. 

In this chapter, we have learned about the photoelectric effect and its impact on the formulation of light as photons. We have also seen that some anomalous electron configurations of the elements are particularly favorable if each atom has one or more half-filled shell, such as the case for the Cr atom with its [Ar]4s 3d electron configuration. Let s suppose it is hypothesized that it requires more energy to remove an electron from a metal that has atoms with one or more half-filled shells than from those that do not (a) Design a series of experiments involving the photoelectric effect that would test the hypothesis, (b) What experimental apparatus would be needed to test the hypothesis It s not necessary that you name actual equipment but rather that you imagine how the apparatus would work—think in terms of the types of measurements that would be needed, and what capability you would need in your apparatus, (c) Describe the type of data you would collect and how you would analyze the data to see whether the hypothesis were correct, (d) Could your experiments be extended to test the hypothesis for other parts of the periodic table, such as the lanthanide or actinide elements ... 

There are, however, two unexpected or anomalous electron configurations that break the Aufbau principle, namely, those of chromium and copper. A simple explanation to explain the existence of these electronic arrangements is to suggest that half-filled and filled 3d sub-levels are both particularly stable electron configurations. 

Which of the transition elements in the first transition series have anomalous electron configurations ... 

The change in the electronic configurations in the case of molybdenum and silver is due to the stability associated with half completed and completed subshells. The anomalous electronic configuration of Nb, Ru, Rh and Pd is due to nuclear electronic attractions and interelectronic repulsions. 

A few studies are starting to claim correlations between nuclear structure and electronic configurations such as the occurrence of anomalous configurations in atoms [41-43]. 

Table B.l. The currently known chemical elements, showing atomic number (Z), chemical symbol, name, relative atomic mass, ground-state electron configuration, and APH indices (t = turn number l-n = angular number) asterisks (, ) symbolize anomalous (APH non-conforming) ground-state electronic configurations, which are indicative of configurational near-degeneracy...

The dipole moments of CO and NO are 0.1 D and 0.166 D. respectively. The oxygen atom is the positive end of the CO dipole, despite the difference in electronegativity coefficients of the two atoms which would imply the opposite conclusion. Consider the electronic configurations of the two molecules, and explain the anomalous properties of the CO molecule. 

PROBLEM 5.20 Look at the electron configurations in Figure 5.17, and identify the 19 anomalous ones. 

The sensitivity of electronic configurations to gravitational fields offers an immediate explanation of the enormously different red shifts of light emitted by a quasar and by less massive objects, physically associated with the quasar. The furore [106] over the anomalous Fraunhofer lines of common metals in a quasar corona could also be defused by the conclusion that the electron configurations of elements within the quasar, and hence their spectroscopic properties, differ from their laboratory equivalents. The observed shifts are therefore not due to a fine-structure constant changing with time, but to the response of electronic energy levels to high pressure. 

---