Chlorine (Cl), neon (Ne), and helium (He) all exist as gases, but only one of them is diatomic. Which is it, and why is it diatomic while the others are monatomic?

To determine the electronic configurations of chlorine (Cl), neon (Ne), and helium (He), we need to refer to the periodic table. The atomic numbers for these elements are Chlorine: 17, Neon: 10, and Helium: 2. Now, let's write their electronic configurations: - Chlorine (Cl): \(1s^2 2s^2 2p^6 3s^2 3p^5\) - Neon (Ne): \(1s^2 2s^2 2p^6\) - Helium (He): \(1s^2\)

We can now discuss the bonding behavior of the three elements based on their electronic configurations. The most stable state for any element is to have a full valence electron shell (either by sharing, gaining, or losing electrons). For Noble gases (Group 18 elements), they are already stable due to having full valence shells. - Chlorine (Cl): With 7 valence electrons (in the 3p subshell), chlorine needs 1 more electron to achieve a full valence electron shell (3p6). Chlorine can achieve this by sharing 1 electron with another chlorine atom, forming a diatomic molecule, Cl2. - Neon (Ne): Neon has a full valence electron shell (2s^2 2p^6). Since it already has a stable electron configuration, it does not need to bond with other atoms. As a result, Neon exists as a monatomic gas. - Helium (He): Helium also has a full valence shell (1s^2), making it stable and not requiring any bonding with other atoms. Therefore, it exists as a monatomic gas.

Based on our analysis in Steps 1 and 2, we can now determine that chlorine (Cl) is the diatomic element among the three given elements (Cl2). The reason for chlorine being diatomic is that it requires one more electron to achieve a stable electron configuration with a full valence shell. By sharing its electrons with another chlorine atom, it forms a diatomic molecule (Cl2). In contrast, neon (Ne) and helium (He) exist as monatomic gases due to their already stable electron configuration with full valence electron shells. Since they are already stable, there is no need for them to bond with other atoms, resulting in their existence as monatomic gases.