Which of the following will have the most negative electron gain enthalpy and which have the least negative? `P, S, Cl, F`. Explain your answer.

Explanation

To determine which of the elements P (phosphorus), S (sulfur), Cl (chlorine), and F (fluorine) has the most negative and least negative electron gain enthalpy, we can follow these steps:

### Step 1: Understand Electron Gain Enthalpy
Electron gain enthalpy is the energy change when an electron is added to a neutral atom in the gas phase. A more negative value indicates that energy is released when the electron is added, making the atom more stable.

### Step 2: Analyze the Trend in the Periodic Table
- As we move from left to right across a period, the electron gain enthalpy generally becomes more negative. This is because atoms have a higher effective nuclear charge, which attracts additional electrons more strongly.
- As we move down a group, the electron gain enthalpy becomes less negative. This is due to the increased distance of the added electron from the nucleus and increased electron-electron repulsion in larger atoms.
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