Problem 53 - Chemistry Central Science

Question

While the electron affinity of bromine is a negative quantity, it is positive for Kr. Use the electron configurations of the two elements to explain the difference.

Step-by-Step Solution

Answer

The difference in electron affinity between bromine and krypton can be explained by their electron configurations. Bromine, with an electron configuration of \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^5\), has one empty spot in its 4p subshell. Adding an electron makes it more stable, releasing energy and resulting in a negative electron affinity. In contrast, krypton's electron configuration is \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6\), with a fully filled 4p subshell. Adding an electron requires it to go into a higher energy, less stable 5s subshell, thus requiring energy input and causing a positive electron affinity.

Step 1: Determine the electron configurations of bromine and krypton

To analyze the difference in electron affinity between bromine and krypton, we first need to know their electron configurations. Bromine (Br) has an atomic number of 35, while krypton (Kr) has an atomic number of 36. Their electron configurations are as follows: Bromine (Br): \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^5\) Krypton (Kr): \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6\)

Step 2: Analyze the electron configurations

Looking at the electron configurations, we can see that bromine has 5 electrons in its 4p subshell, while krypton has a completely filled 4p subshell with 6 electrons. Bromine has one empty spot in its 4p subshell, which means adding an electron to bromine will complete its 4p subshell, making it more stable. This process releases energy, resulting in a negative electron affinity. On the other hand, krypton's 4p subshell is already full. Adding an additional electron would require it to go into the next higher energy subshell (5s), which is less stable. This process requires energy, causing the electron affinity of krypton to be positive.

Step 3: Relate electron configurations to electron affinity

In summary, the difference in electron affinity between bromine and krypton can be explained by their electron configurations: - Bromine readily accepts an additional electron to complete its 4p subshell, releasing energy in the process. This results in a negative electron affinity. - Krypton's 4p subshell is already full, so adding an electron requires it to go into a higher energy subshell (5s), making the atom less stable. This process requires energy input, resulting in a positive electron affinity.