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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

The element strontium is used in a variety of industrial processes. It is not an extremely hazardous substance, but low levels of strontium ingestion could affect the health of children. Radioactive strontium is very hazardous, it was a by-product of nuclear weapons testing and was found widely distributed following nuclear tests. Calcium is quite common in the environment, including food products, and is frequently present in drinking water. Discuss the similarities and differences between calcium and strontium, and indicate how and why strontium might be expected to accompany calcium in water supplies, uptake by plants, and so on.

The following table gives the electron affinities, in \(\mathrm{kJ} / \mathrm{mol}\), for the group \(1 \mathrm{~B}\) and group \(2 \mathrm{~B}\) metals: (a) Why are the electron affinities of the group \(2 \mathrm{~B}\) elements greater than zero? (b) Why do the electron affinities of the group \(1 \mathrm{~B}\) elements become more negative as we move down the group? [Hint: Examine the trends in the electron affinity of other groups as we proceed down the periodic table.] \begin{tabular}{|c|l|} \hline \(\mathrm{Cu}\) & \multirow{2}{*} { \(\mathrm{Zn}\) \(-119\)} & \(>0\) \\ \hline \(\mathrm{Ag}\) & \(\mathrm{Cd}\) \\ \(-126\) & \(>0\) \\ \hline \(\mathrm{Au}\) & \(\mathrm{Hg}\) \\ \(-223\) & \(>0\) \\ \hline \end{tabular}

There are certain similarities in properties that exist between the first member of any periodic family and the element located below it and to the right in the periodic table. For example, in some ways Li resembles \(\mathrm{Mg}\), Be resembles \(\mathrm{Al}\), and so forth. This observation is called the diagonal relationship. Using what we have learned in this chapter, offer a possible explanation for this relationship.

(a) Because an exact outer boundary cannot be measured or even calculated for an atom, how are atomic radii determined? (b) What is the difference between a bonding radius and a nonbonding radius? (c) For a given element, which one is larger?

Write a balanced equation for the reaction that occurs in each of the following cases: (a) Potassium metal burns in an atmosphere of chlorine gas, (b) Strontium oxide is added to water. (c) A fresh surface of lithium metal is exposed to oxygen gas. (d) Sodium metal is reacted with molten sulfur.
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