Define electron affinity, and explain why Na has a less exothermic value than Cl in terms of ion stability (Na-1)
I know the definition part is Na less esothermic because Na has more energy? But why?
Electron affinity refers to the energy change that occurs when a neutral atom in the gas phase gains an electron to form a negative ion. It is a measure of how likely an atom is to accept an additional electron. A more negative electron affinity value indicates a higher affinity for electrons.
Now, let's look at why sodium (Na) has a less exothermic value than chlorine (Cl) in terms of ion stability.
To understand this, we need to consider the electron configuration of these elements. Sodium has an atomic number of 11, meaning it has 11 electrons. Its electron configuration is 1s² 2s² 2p⁶ 3s¹, where the outermost electron is in the 3s orbital. Chlorine, on the other hand, has an atomic number of 17 and an electron configuration of 1s² 2s² 2p⁶ 3s² 3p⁵, with the outermost electron in the 3p orbital.
When an atom gains an electron, it enters a lower energy level or orbital. In the case of sodium (Na), if it gains an electron, it would need to place that electron in a higher energy level orbital (3p) compared to its original outermost electron orbital (3s). This results in a higher energy arrangement, making it less stable. Hence, sodium has a less exothermic value for electron affinity.
In contrast, chlorine (Cl) already has an electron in the 3p orbital. So, when it gains an electron, it can add it to the same orbital, resulting in a more stable electron configuration. Thus, chlorine has a more exothermic value for electron affinity compared to sodium.
Therefore, the difference in electron affinity values between sodium and chlorine can be attributed to the stability of their respective negative ions (Na-1 and Cl-1) based on the arrangement of electrons in their outermost energy levels.