Electron gain enthalpy with negative sign of fluorine is less than that of chlorine due to :
The electron gain enthalpy order for halogens is
Cl > F > Br > I
Due to small size of fluorine the extra electron to be added feels more electron-electron repulsion. Therefore fluorine has less value for electron affinity than chlorine.
Electron gain enthalpy (EGE) is the energy change when an atom gains an electron to form a negative ion. A more negative EGE indicates greater tendency to gain electrons. Fluorine has less negative EGE than chlorine due to its smaller atomic size.
Step 1: Understand atomic size trend - Fluorine (atomic number 9) is smaller than chlorine (atomic number 17) in the same group (17).
Step 2: In smaller atoms like fluorine, electron density is higher, leading to greater electron-electron repulsion when adding an extra electron.
Step 3: This repulsion reduces the energy released (makes EGE less negative), despite higher effective nuclear charge.
Step 4: Chlorine's larger size allows better accommodation of the extra electron with less repulsion.
Final Answer: The correct reason is Smaller size of fluorine atom
Electron Gain Enthalpy Definition:
Factors affecting EGE:
Trend in Group 17: EGE becomes more negative from F to Cl, then decreases down the group due to increasing atomic size.