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Chapter 2: Problem 115

The first ionization energies of As and Se are 0.947 and \(0.941 \mathrm{MJ} / \mathrm{mol},\) respectively. Rationalize these values in terms of electron configurations.

Short Answer

Expert verified
The first ionization energies of As and Se can be rationalized by examining their electron configurations. As (atomic number 33) has an electron configuration of \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^3\), while Se (atomic number 34) has an electron configuration of \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^4\). In both cases, the outermost electron is in the 4p orbital; however, Se has more electron repulsion in the 4p orbital due to having four electrons there. This increased repulsion makes it slightly easier to remove an electron from Se, resulting in a lower first ionization energy (0.941 MJ/mol) compared to As (0.947 MJ/mol).

Step by step solution

01

Determine the electron configurations

To begin, we must determine the electron configurations of As and Se. Use the periodic table to find their atomic numbers and write the electron configurations accordingly. As (Atomic number: 33): \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^3\) Se (Atomic number: 34): \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^4\)
02

Relate electron configurations to first ionization energies

First ionization energies are related to the difficulty of removing one electron from the atom. Electrons closer to the nucleus or with less shielding are more difficult to remove, causing higher ionization energies. We should analyze the shielding and effective nuclear charge for the outermost electrons of As and Se. - As: The outermost electron is in the 4p orbital, and it has 3 electrons there. It experiences shielding from the 1s, 2s, 2p, 3s, 3p, 4s, and 3d orbitals. - Se: The outermost electron is also in the 4p orbital, and it has 4 electrons there. It experiences shielding from the same orbitals as As.
03

Compare the stability of the outermost electrons

In As, the outermost electron occupies one of the three degenerate 4p orbitals, so it experiences less repulsion from other electrons than in Se. In Se, the outermost electron is in a 4p orbital with an additional electron, which means it experiences more repulsion from other electrons. This electron repulsion increases the shielding effect and makes it slightly easier to remove an electron from Se compared to As. As a result, we should expect Se to have a slightly lower first ionization energy than As due to its electron configuration and the increased electron repulsion it experiences.
04

Compare the given ionization energies

According to the given ionization energies, As has a first ionization energy of 0.947 MJ/mol, while Se has a first ionization energy of 0.941 MJ/mol. This confirms our analysis, as Se has a lower first ionization energy than As, which can be rationalized by considering their electron configurations and the repulsion their outermost electrons experience.

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Most popular questions from this chapter

An unknown element is a nonmetal and has a valence electron configuration of \(n s^{2} n p^{4}\). a. How many valence electrons does this element have? b. What are some possible identities for this element? c. What is the formula of the compound this element would form with potassium? d. Would this element have a larger or smaller radius than barium? e. Would this element have a greater or smaller ionization energy than fluorine?

A carbon-oxygen double bond in a certain organic molecule absorbs radiation that has a frequency of \(6.0 \times 10^{13} \mathrm{s}^{-1}\). a. What is the wavelength of this radiation? b. To what region of the spectrum does this radiation belong? c. What is the energy of this radiation per photon? d. A carbon-oxygen bond in a different molecule absorbs radiation with frequency equal to \(5.4 \times 10^{13} \mathrm{s}^{-1} .\) Is this radiation more or less energetic?

The four most abundant elements by mass in the human body are oxygen, carbon, hydrogen, and nitrogen. These four elements make up about \(96 \%\) of the human body. The next four most abundant elements are calcium, phosphorus, magnesium, and potassium. Write the expected ground-state electron configurations for these eight most abundant elements in the human body.

In each of the following sets, which atom or ion has the smallest radius? a. \(\mathrm{H}, \mathrm{He}\) b. \(\mathrm{Cl}, \mathrm{In}, \mathrm{Se}\) c. element \(120,\) element \(119,\) element 116 d. \(\mathrm{Nb}, \mathrm{Zn}, \mathrm{Si}\) e. \(\mathrm{Na}^{-}, \mathrm{Na}, \mathrm{Na}^{+}\)

Order the atoms in each of the following sets from the least negative electron affinity to the most. a. \(\mathrm{S}, \mathrm{Se}\) b. \(\mathrm{F}, \mathrm{Cl}, \mathrm{Br}, \mathrm{I}\)
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