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Chapter 7: Problem 52

The electron affinity of lithium is a negative value, whereas the electron affinity of beryllium is a positive value. Use electron configurations to account for this observation.

Short Answer

Expert verified
Lithium has a negative electron affinity because adding an electron to its 1s虏 2s鹿 configuration results in a stable, complete s-subshell (1s虏 2s虏). In contrast, beryllium has a positive electron affinity because adding an electron to its already-stable 1s虏 2s虏 configuration would result in an unstable 1s虏 2s虏 2p鹿 configuration, requiring an input of energy. This difference in electron configurations accounts for the different signs of their electron affinities.

Step by step solution

01

Determine the electron configurations of lithium and beryllium

In order to determine the electron configurations of lithium and beryllium, we need to follow the periodic table. Lithium (Li) has an atomic number of 3, meaning it has 3 electrons. Its electron configuration is 1s虏 2s鹿. Beryllium (Be) has an atomic number of 4, meaning it has 4 electrons. Its electron configuration is 1s虏 2s虏. Now that we have the electron configurations, let's take a look at their electron affinities.
02

Explain the negative electron affinity of lithium

Electron affinity is the energy change that occurs when an electron is added to a gaseous atom. Lithium has a negative electron affinity, implying that energy is released when an electron is added to it. In the case of lithium, when an electron is added, the electron configuration becomes 1s虏 2s虏, which corresponds to a stable and complete s-subshell. This results in a release of energy, leading to a negative electron affinity.
03

Explain the positive electron affinity of beryllium

Beryllium has a positive electron affinity, which means that energy is required to add an electron to it. Beryllium already has a complete and stable 2s虏 subshell. Adding an electron to beryllium would create a 2p鹿 electron configuration. This results in an unstable and higher energy configuration, requiring an input of energy. Thus, beryllium's electron affinity is positive.
04

Conclude

Lithium's electron affinity is negative because adding an electron to it results in a stable, lower-energy electron configuration (1s虏 2s虏). On the other hand, beryllium's electron affinity is positive because adding an electron to it leads to an unstable, higher-energy electron configuration (1s虏 2s虏 2p鹿). This difference in electron configurations is responsible for the observed difference in the electron affinities of lithium and beryllium.

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Most popular questions from this chapter

(a) Why are ionization energies always positive quantities? (b) Why does \(\mathrm{F}\) have a larger first ionization energy than \(\mathrm{O}\) ? (c) Why is the second ionization energy of an atom always greater than its first ionization energy?

When magnesium metal is burned in air (Figure 3.5), two products are produced. One is magnesium oxide, \(\mathrm{MgO}\). The other is the product of the reaction of \(\mathrm{Mg}\) with molecular nitrogen, magnesium nitride. When water is added to magnesium nitride, it reacts to form magnesium oxide and ammonia gas. (a) Based on the charge of the nitride ion (Table 2.5), predict the formula of magnesium nitride. (b) Write a balanced equation for the reaction of magnesium nitride with water. What is the driving force for this reaction? (c) In an experiment a piece of magnesium ribbon is burned in air in a crucible. The mass of the mixture of \(\mathrm{MgO}\) and magnesium nitride after burning is \(0.470 \mathrm{~g}\). Water is added to the crucible, further reaction occurs, and the crucible is heated to dryness until the final product is \(0.486 \mathrm{~g}\) of \(\mathrm{MgO}\). What was the mass percentage of magnesium nitride in the mixture obtained after the initial burning? (d) Magnesium nitride can also be formed by reaction of the metal with ammonia at high temperature. Write a balanced equation for this reaction. If a \(6.3-\mathrm{g} \mathrm{Mg}\) ribbon reacts with \(2.57 \mathrm{~g} \mathrm{NH}_{3}(\mathrm{~g})\) and the reaction goes to \(\mathrm{com}\) pletion, which component is the limiting reactant? What mass of \(\mathrm{H}_{2}(\mathrm{~g})\) is formed in the reaction? (e) The standard enthalpy of formation of solid magnesium nitride is \(-461.08 \mathrm{~kJ} / \mathrm{mol}\). Calculate the standard enthalpy change for the reaction between magnesium metal and ammonia gas.

In Chapter 1 we learned that silicon is the second most abundant element in Earth's crust, accounting for more than one-fourth of the mass of the crust (Figure 1.6). Yet we see that silicon is not among the elements that have been known since ancient times (Figure \(7.2\) ), whereas iron, which accounts for less than \(5 \%\) of Earth's crust, has been known since prehistoric times. Given silicon's abundance how do you account for its relatively late discovery?

Some metal oxides, such as \(\mathrm{Sc}_{2} \mathrm{O}_{3}\), do not react with pure water, but they do react when the solution becomes either acidic or basic. Do you expect \(\mathrm{Sc}_{2} \mathrm{O}_{3}\) to react when the solution becomes acidic or when it becomes basic? Write a balanced chemical equation to support your answer.

(a) Among the nonmetallic elements, the change in atomic radius in moving one place left or right in a row is smaller than the change in moving one row up or down. Explain these observations. (b) Arrange the following atoms in order of increasing atomic radius: \(S i\). \(\mathrm{A} 1\), Ge, Ga.
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