Question

The correct statement among the following is (1) Electron affinity of \(X^{-}\) ion is cqual to ionisation energy of \(X\) atom. (2) The sccond clectron gain cnthalpy is more than the first clectron gain enthalpy. (3) Among the metals gold has maximum clectron affinity. (4) Electron affinity of fluorine is more than that of chlorinc duc to lower size.

Short answer

Option 2: The second electron gain enthalpy is more than the first electron gain enthalpy.

Step-by-step solution

Analyze Option 1

Option 1 states that the electron affinity of the ion \(X^{-}\) is equal to the ionization energy of the atom \(X\). Electron affinity refers to the energy change when an electron is added to an atom, while ionization energy refers to the energy required to remove an electron. These are opposite processes and thus not equal.

Analyze Option 2

Option 2 states that the second electron gain enthalpy is more than the first electron gain enthalpy. This is correct because adding an electron to a negatively charged ion is more difficult and requires more energy than adding an electron to a neutral atom.

Analyze Option 3

Option 3 states that among metals, gold has the maximum electron affinity. This is incorrect because electron affinity generally decreases down a group, and there are other metals like nonmetals that have higher electron affinities than gold.

Analyze Option 4

Option 4 states that the electron affinity of fluorine is more than that of chlorine due to its lower size. This is incorrect because, despite the smaller size of fluorine, chlorine has a higher electron affinity because it can better accommodate the additional electron.

Conclusion

From the analysis above, the correct statement is Option 2: 'The second electron gain enthalpy is more than the first electron gain enthalpy.'

Key concepts

Electron Affinity

Electron affinity measures how much energy is released when an electron is added to a neutral atom, forming a negatively charged ion. It’s like a welcome party for electrons. Different elements release different amounts of energy when they gain an electron. This amount can tell us how much an atom 'wants' an extra electron.
Atoms with high electron affinity release more energy, meaning they strongly attract additional electrons. Nonmetals often have higher electron affinities than metals because they are closer to completing their outer electron shells.
For gases like chlorine, electron affinity plays a huge role. Chlorine releases a lot of energy when it gains an electron, indicating its high electron affinity. Fluorine, however, releases less energy compared to chlorine due to its smaller size which causes higher electron-electron repulsion in the compact space available.

Ionization Energy

Ionization energy is the energy required to remove an electron from a neutral atom in the gas phase, turning it into a positively charged ion. If you think about electron affinity as a welcome party, ionization energy is like a breakup that needs extra effort.
The first ionization energy is always less than the second because the remaining electrons are held more tightly by the effective nuclear charge. This means it’s easier to remove the first electron than the second. Ionization energy increases across a period (left to right) due to greater nuclear charge holding the electrons tighter. It decreases down a group since the electrons are further from the nucleus and are easier to remove.
Higher ionization energies are observed in nonmetals, especially in noble gases, because they have nearly full outer shells and thus strongly resist losing electrons.

Electron Gain Enthalpy

Electron gain enthalpy (or electron affinity) refers to the energy change when an electron is added to a neutral atom to form an anion. When the process is exothermic (energy is released), electron gain enthalpy is negative, indicating a favorable process. In contrast, if energy is required (an endothermic process), the electron gain enthalpy is positive.
The first electron gain enthalpy is usually negative because most atoms release energy when they first gain an electron. However, the second electron gain enthalpy is positive because adding another electron to an already negatively charged ion requires extra energy to overcome the repulsive force between the negative charges. This explains why the second electron gain enthalpy is more than the first.

• Example: Oxygen has a negative first electron gain enthalpy but a positive second electron gain enthalpy due to increased electron repulsion.

Periodic Trends

Periodic trends describe how certain properties of elements change in a predictable manner across the periodic table. Key trends include:

• Ionization Energy: Increases across a period due to increasing nuclear charge and decreases down a group due to increasing distance from the nucleus.
• Electron Affinity: Generally becomes more negative across a period, indicating stronger attraction for additional electrons, and less negative down a group due to increasing atomic size and electron-electron repulsion.
• Atomic Radius: Decreases across a period as electrons are pulled closer to the nucleus and increases down a group as additional electron shells are added.
• Electronegativity: Tends to increase across a period and decrease down a group, indicating how strongly atoms attract bonding electrons.

Understanding these periodic trends helps in predicting the behavior of different elements during chemical reactions and bonding.