Question

The false statement among the following is (1) Electron affinity of noble gases is almost zero. (2) The halogen with highest electron affinity is fluorine. (3) Electron affinity values are obtained indirectly by Born-Haber Cycle. (4) lonisation potential of Na would be numerically the same as electron affinity of \(\mathrm{Na}^{+}\).

Short answer

Statement 2 is false.

Step-by-step solution

Understanding Electron Affinity

Electron affinity is the energy change that occurs when an electron is added to a neutral atom. Noble gases typically have nearly zero electron affinity because they have a complete valence shell.

Analyzing Statement 1

The first statement says: 'Electron affinity of noble gases is almost zero.' This is true, as noble gases have stable electron configurations and do not gain electrons easily.

Analyzing Statement 2

The second statement says: 'The halogen with the highest electron affinity is fluorine.' This is incorrect. While fluorine is highly reactive, chlorine has a higher electron affinity due to less electron-electron repulsion in its larger atomic size.

Analyzing Statement 3

The third statement says: 'Electron affinity values are obtained indirectly by Born-Haber Cycle.' This is true. The Born-Haber cycle is used to calculate lattice energy and can indirectly determine electron affinity.

Analyzing Statement 4

The fourth statement says: 'Ionisation potential of Na would be numerically the same as electron affinity of \( \text{Na}^{+} \).' This is true since ionization potential of a neutral atom is numerically equal to the electron affinity of the corresponding cation formed.

Identifying the False Statement

From the above analysis, the false statement is 'The halogen with the highest electron affinity is fluorine.'

Key concepts

noble gases electron affinity

Electron affinity refers to the energy change that happens when an electron is added to a neutral atom. Noble gases, such as helium, neon, and argon, have a complete valence shell, making their electron affinity nearly zero. They are very stable and do not easily gain or lose electrons.
Because of their full outer shell, the energy required to add an electron is very high, which means it is energetically unfavorable. Hence, their electron affinity values are almost zero. This stability is why noble gases are often found in their elemental form in nature.

halogen electron affinity

Halogens include fluorine, chlorine, bromine, iodine, and astatine. These elements have high electron affinities because they are just one electron short of a complete valence shell.
Among the halogens, chlorine actually has the highest electron affinity, not fluorine. This might sound surprising because fluorine is the most electronegative element. However, the small size of fluorine leads to significant electron-electron repulsion when it gains an extra electron. This repulsion reduces the energy released compared to chlorine, which has a larger size and less repulsion.

Born-Haber Cycle

The Born-Haber Cycle is a theoretical model used to analyze the formation of ionic compounds. It helps to determine various energy changes, including electron affinities and lattice energies. This cycle consists of several steps, starting from the elements in their standard state and ending with the formation of an ionic compound.
By using Hess’s law, the cycle relates the lattice energy of an ionic crystal to the enthalpy changes involved, such as ionization energies, electron affinities, and sublimation energies. Therefore, electron affinity values can indeed be obtained indirectly through the Born-Haber Cycle.

ionisation potential

Ionization potential, or ionization energy, is the energy required to remove an electron from a neutral atom. For sodium (Na), the ionization potential is the energy needed to remove one electron to form Na⁺.
Interestingly, the electron affinity of Na⁺ (the energy change when an electron is added to Na⁺) is numerically equal to the ionization potential of the neutral Na atom. This is because both processes involve moving an electron between the same two states, just in opposite directions.