Problem 73 - Chemistry: The Central Science

Question

Compare the elements bromine and chlorine with respect to the following properties: (a) electron configuration, (b) most common ionic charge, (c) first ionization energy, (d) reactivity toward water, (e) electron affinity, (f) atomic radius. Account for the differences between the two elements.

Step-by-Step Solution

Answer

Both Bromine (Br) and Chlorine (Cl) are in group 7A of the periodic table and have 7 valence electrons. They both possess a common ionic charge of -1. However, Chlorine has higher ionization energy, reactivity toward water, and electron affinity due to its position above Bromine in the periodic table. In contrast, Bromine has a larger atomic radius because of an increased number of electron shells as we move down the group.

Step 1: (a) Electron Configuration

Let's first write the electron configurations for both elements. Bromine (Br) has an atomic number of 35. Its electron configuration is given by: \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^5.\] Chlorine (Cl) has an atomic number of 17. Its electron configuration is given by: \[1s^2 2s^2 2p^6 3s^2 3p^5.\] Both elements are found in the same group (group 7A) in the periodic table, and therefore have the same number of valence electrons, which in this case is 7.

Step 2: (b) Most Common Ionic Charge

Considering they both are in group 7A, they tend to gain an electron to have a complete outer shell, and therefore, the most common ionic charge for both elements is -1.

Step 3: (c) First Ionization Energy

Ionization energy is the energy required to remove an electron from an atom in the gas phase. As we move up a group in the periodic table, the ionization energy increases. Since Chlorine is above Bromine in group 7A, Chlorine has a higher first ionization energy.

Step 4: (d) Reactivity Toward Water

Both Chlorine and Bromine react with water. However, Chlorine is more reactive than Bromine. One of the reasons for this is the higher electronegativity found in Chlorine, which promotes a greater tendency to react with water.

Step 5: (e) Electron Affinity

Electron affinity is the energy change when an electron is added to an atom. Generally, electron affinity increases across periods and decreases down a group. Since Chlorine is above Bromine, Chlorine has a higher electron affinity.

Step 6: (f) Atomic Radius

The atomic radius is the distance from the nucleus to the outermost electron shell. As we move down a group in the periodic table, the atomic radius increases. This is due to the increasing number of electron shells as we move down the group. Bromine has a larger atomic radius compared to Chlorine. In conclusion, both Bromine and Chlorine are found in group 7A and therefore share similar characteristics in terms of valence electrons and common ionic charges. However, there are differences between the two elements, with Chlorine having higher ionization energy, reactivity toward water, and electron affinity, while Bromine has a larger atomic radius. These differences can be attributed to the positions of the two elements in the periodic table, with Chlorine located above Bromine.