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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

Make a simple sketch of the shape of the main part of the periodic table, as shown (a) Ignoring \(\mathrm{H}\) and \(\mathrm{He}\), write a single straight arrow from the element with the smallest bonding atomic radius to the element with the largest. (b) Ignoring \(\mathrm{H}\) and \(\mathrm{He}\), write a single straight arrow from the element with the smallest first ionization energy to the element with the largest. (c) What significant observation can you make from the arrows you drew in parts (a) and (b)? [Sections \(7.3\) and 7.4]

Little is known about the properties of astatine, At, because of its rarity and high radioactivity. Nevertheless, it is possible for us to make many predictions about its properties. (a) Do you expect the element to be a gas, liquid, or solid at room temperature? Explain. (b) What is the chemical formula of the compound it forms with Na?

Arrange the following oxides in order of increasing acidity: \(\mathrm{CO}_{2}, \mathrm{CaO}, \mathrm{Al}_{2} \mathrm{O}_{3}, \mathrm{SO}_{3}, \mathrm{SiO}_{2}\), and \(\mathrm{P}_{2} \mathrm{O}_{5}\)

Why did Mendeleev leave blanks in his early version of the periodic table? How did he predict the properties of the elements that belonged in those blanks?

(a) Why is cesium more reactive toward water than is lithium? (b) One of the alkali metals reacts with oxygen to form a solid white substance. When this substance is dissolved in water, the solution gives a positive test for hydrogen peroxide, \(\mathrm{H}_{2} \mathrm{O}_{2}\). When the solution is tested in a burner flame, a lilac-purple flame is produced. What is the likely identity of the metal? (c) Write a balanced chemical equation for reaction of the white substance with water.
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