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The first ionization energy and electron affinity of Ar are both positive values. (a) What is the significance of the positive value in each case? (b) What are the units of electron affinity?

Short Answer

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(a) In the case of ionization energy, a positive value signifies that energy is required to remove an electron from the atom, indicating the atom's stability and reluctance to lose electrons. For electron affinity, a positive value indicates that energy is released when an electron is added, meaning the atom is less likely to accept additional electrons. Argon, a noble gas, does not readily lose or gain electrons to attain stability. (b) The units of electron affinity correspond to energy units, such as electron volts (eV), kilojoules per mole (kJ/mol), or joules per mole (J/mol).

Step by step solution

01

(a) Significance of the Positive Value

In the case of ionization energy, a positive value signifies that energy is required to remove an electron from the atom, i.e., it takes energy to ionize the atom. It means the atom is stable and not prone to losing electrons easily, which is true for noble gases like Argon. They have a stable electron configuration and do not tend to lose or gain electrons readily. For electron affinity, a positive value indicates that energy is released when an electron is added to the atom, i.e., the atom can gain energy when an electron is added to it. This means that the atom is less likely to accept additional electrons. In the case of Argon, it is a noble gas with a full valence shell, so it does not need to gain any more electrons to attain a stable configuration.
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(b) Units of Electron Affinity

The units for electron affinity are the same as those used for energy, as electron affinity measures the energy change associated with adding an electron to an atom. Common units for electron affinity include electron volts (eV), kilojoules per mole (kJ/mol), or joules per mole (J/mol).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Ionization Energy
Ionization energy is a fundamental concept in chemistry that refers to the energy required to remove an electron from an atom or ion in its gaseous state. An atom's ionization energy is a reflection of its stability and reactivity. When we observe a positive ionization energy, this indicates an input of energy is necessary to overcome the attraction between the negatively charged electron and the positively charged nucleus.

A higher ionization energy suggests that an atom holds its electrons more tightly, which usually infers high stability and low reactivity. This trend is evident in noble gases, which have relatively high ionization energies due to their stable electron configurations. For instance, Argon (Ar) has a high first ionization energy because its electrons are in a full valence shell, making them less prone to being removed.

The concept of ionization energy is crucial in predicting the chemical behavior of elements, particularly in forming ions during chemical reactions. It is also an essential factor in understanding periodic trends across the periodic table, where ionization energy generally increases across a period and decreases down a group.
Noble Gases
Noble gases are a unique group of elements characterized by their lack of reactivity, which results from their complete valence electron shells. Elements such as Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn) make up this group in the periodic table.

Due to their filled electron shells, noble gases have no tendency to gain or lose electrons, making their ionization energy and electron affinity values noteworthy. For instance, Argon's positive ionization energy indicates its reluctance to release electrons, underscoring its stability and inertness. These gases do not readily form compounds with other elements under standard conditions, and their inert nature has led to extensive applications, including providing non-reactive environments in light bulbs and protecting delicate electronic components.
Energy Units
In the context of chemistry and physics, energy units are used to quantify the amount of energy associated with various phenomena, including ionization energy and electron affinity. These units can appear in various forms, such as electron volts (eV), which are commonly used in atomic and nuclear physics, joules (J), a standard unit in the International System of Units (SI), or kilojoules per mole (kJ/mol), frequently used for quantifying energy changes in chemical reactions.

One electron volt (eV) is defined as the amount of kinetic energy gained or lost by an electron as it moves through an electric potential difference of one volt. On the other hand, a joule is a more general unit defined as the energy transferred when a force of one newton moves an object one meter. In chemistry, energy changes are often discussed on a per-mole basis, making kJ/mol a practical unit when considering substances' thermodynamic properties or reactions involving moles of substances.

Regardless of the unit used, understanding energy in its various forms and measurements is critical in grasping how atoms and molecules interact, how reactions occur, and how energy is conserved in physical and chemical processes.

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Most popular questions from this chapter

Chlorine reacts with oxygen to form \(\mathrm{Cl}_{2} \mathrm{O}_{7} .\) (a) What is the name of this product (see Table 2.6 )? (b) Write a balanced equation for the formation of \(\mathrm{Cl}_{2} \mathrm{O}_{7}(l)\) from the elements. (c) Under usual conditions, \(\mathrm{Cl}_{2} \mathrm{O}_{7}\) is a colorless liquid with a boiling point of \(81^{\circ} \mathrm{C}\). Is this boiling point expected or surprising? (d) Would you expect \(\mathrm{Cl}_{2} \mathrm{O}_{7}\) to be more reactive toward \(\mathrm{H}^{+}(a q)\) or \(\mathrm{OH}^{-}(a q) ?\) Explain. (e) If the oxygen in \(\mathrm{Cl}_{2} \mathrm{O}_{7}\) is considered to have the -2 oxidation state, what is the oxidation state of the Cl? What is the electron configuration of \(\mathrm{Cl}\) in this oxidation state?

Use electron configurations to explain the following observations: (a) The first ionization energy of phosphorus is greater than that of sulfur. (b) The electron affinity of nitrogen is lower (less negative) than those of both carbon and oxygen. (c) The second ionization energy of oxygen is greater than the first ionization energy of fluorine. (d) The third ionization energy of manganese is greater than those of both chromium and iron.

(a) Write the electron configuration for \(\mathrm{Li}\), and estimate the effective nuclear charge experienced by the valence electron. (b) The energy of an electron in a one-electron atom or ion equals \(\left(-2.18 \times 10^{-18} \mathrm{~J}\right)\left(\frac{Z^{2}}{n^{2}}\right)\) where \(Z\) is the nuclear charge and \(n\) is the principal quantum number of the electron. Estimate the first ionization energy of Li. (c) Compare the result of your calculation with the value reported in Table 7.4 and explain the difference. (d) What value of the effective nuclear charge gives the proper value for the ionization energy? Does this agree with your explanation in \((\mathrm{c}) ?\)

Identify each statement as true or false. If it is false, rewrite it so that it is true: (a) Ionization energies are always negative quantitites. (b) Oxygen has a larger first ionization energy than fluorine. (c) The second ionization energy of an atom is always greater than its first ionization energy.

(a) Why does the quantum mechanical description of manyelectron atoms make it difficult to define a precise atomic radius? (b) When nonbonded atoms come up against one another, what determines how closely the nuclear centers can approach?

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