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.

Short answer

In summary, Bromine (Br) and Chlorine (Cl) are both halogens with similar electron configurations and a most common ionic charge of -1. However, Chlorine has a higher first ionization energy (1251.2 kJ/mol vs. 1139.9 kJ/mol), higher reactivity toward water, higher electron affinity (-349 kJ/mol vs. -324 kJ/mol), and a smaller atomic radius (99 pm vs. 115 pm) than Bromine. These differences are due to Chlorine's higher position in the periodic table, closer proximity to the nucleus, and stronger electron-nucleus attraction.

Step-by-step solution

(a) Electron Configuration

: To compare the electron configurations of Bromine (Br) and Chlorine (Cl), we need to know their atomic numbers. Bromine has an atomic number of 35, while Chlorine has an atomic number of 17. Bromine (Br, atomic number 35) electron configuration: \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^5\] Chlorine (Cl, atomic number 17) electron configuration: \[1s^2 2s^2 2p^6 3s^2 3p^5\] Both Bromine and Chlorine are members of Group 17, the halogens. They share a similar electron configuration in that they both have 7 electrons in the outermost shell (p orbitals), which is one electron short of the stable noble gas configuration.

(b) Most common ionic charge

: Both Bromine and Chlorine are known to form negative ions (-1 charge) when they react with other elements. This is because they readily gain an electron to complete their octet and achieve a noble gas configuration. Bromine most common ionic charge: \(Br^- (Br^{-1})\) Chlorine most common ionic charge: \(Cl^- (Cl^{-1})\)

(c) First Ionization Energy

: First ionization energy refers to the energy required to remove the outermost electron from an atom. Due to Chlorine being higher up in the periodic table (Period 3) than Bromine (Period 4), it is closer to the nucleus and its outer electrons experience a stronger attraction to the nucleus. This means it requires more energy to remove an electron from Chlorine than it does Bromine, resulting in a higher first ionization energy for Chlorine compared to Bromine. Chlorine first ionization energy: \(1251.2 \,kJ/mol\) Bromine first ionization energy: \(1139.9 \,kJ/mol\)

(d) Reactivity Toward Water

: Both Bromine and Chlorine react with water. Chlorine is more reactive than Bromine due to its higher electronegativity and smaller atomic size, allowing it to form stronger bonds with other atoms. Reaction of Bromine with water: \(Br_2 + H_2O \rightarrow HBr + HOBr\) Reaction of Chlorine with water: \(Cl_2 + H_2O \rightarrow HCl + HClO\)

(e) Electron Affinity

: Electron affinity is the energy change associated with an atom gaining an electron. Chlorine has a higher electron affinity than Bromine, as it is closer to the nucleus, leading to a stronger attraction between the nucleus and the additional electron. Chlorine electron affinity: \(-349 \,kJ/mol\) Bromine electron affinity: \(-324 \,kJ/mol\)

(f) Atomic Radius

: The atomic radius of an element is the distance from the nucleus to the outermost electron shell. Bromine has a larger atomic radius than Chlorine because it has more electron shells, causing a greater distance between the nucleus and the outermost electron shell. Bromine atomic radius: \(115 \,pm\) Chlorine atomic radius: \(99 \,pm\) In summary, Bromine and Chlorine share similar electron configurations and most common ionic charge. However, differences in first ionization energy, reactivity toward water, electron affinity, and atomic radius can be attributed to their positions in the periodic table and the resulting differences in the number of electron shells as well as electron-nucleus attraction strength.