Understanding the Electron Gain Enthalpy of Chlorine and Fluorine

Electron gain enthalpy (E?) is a thermodynamic quantity that measures the energy change that occurs when an electron is added to a neutral gaseous atom. For the elements chlorine (Cl) and fluorine (F), there is a significant difference in their electron gain enthalpy values. This difference is primarily due to the difference in their atomic sizes and the resulting electronic configurations.

Factors Influencing Electron Gain Enthalpy

The electron gain enthalpy of an element depends on the amount of energy released when an extra electron is added to the atom. For atomic elements like F and Cl, the primary factors influencing this process include atomic size, electron configuration, and the presence of available orbitals.

Fluorine (F)

Fluorine, being a highly electronegative element, has a small atomic size. This small size leads to significant inter-electronic repulsion when an electron is added to its 2p orbital. The close proximity of the added electron to the existing electrons increases the repulsion, resulting in a less negative electron gain enthalpy for F. The repulsion experienced by the incoming electron in F is due to the repulsion from the pre-existing electrons in the valence shell.

Chlorine (Cl)

Chlorine, with a larger atomic size and a vacant d orbital, provides more space for the added electron. The larger size of chlorine minimizes the inter-electronic repulsion, making it easier for the element to accept an additional electron. The vacant d orbital also aids in the easier acceptance of the electron, contributing to a more negative electron gain enthalpy for Cl.

Theoretical Explanation

The formula used to calculate electron gain enthalpy is given by:

H 0.428Nq2/R kJ/mole

Where:

N is Avogadro's number (6.022 x 1023) q2 is the Coulomb electric charge (2.304 x 10?2? Nm2) R is the ionic radius of the element

This reveals a relationship between the ionic radius and the electron gain enthalpy. Elements with smaller ionic radii, like F, exhibit less electron gain enthalpy due to increased inter-electronic repulsion. Conversely, elements with larger ionic radii, like Cl, exhibit higher electron gain enthalpy because the added electron experiences less repulsion.

Comparative Table

A table below illustrates the variance in the electron gain enthalpy of fluorine, chlorine, bromine, and iodine based on their ionic radii:

ElementR (units)ΔH (units)RxΔH (kJ/mole) F0.9926532839032 Cl1.75779349.360827.43 Br2.96622325.196459.42 I3.00346295.190122.58

It is observed that the value RxΔH for F is significantly lower than for Cl, due to the smaller ionic radius of F. This explains why F has less negative electron gain enthalpy compared to Cl.

Theory Reinterpretation

My theory posits that protons and electrons are ring-shaped cyclones in a universal ideal gas. Accordingly, the configuration of electron rings around a nucleus varies. For elements in Group 17 (Fluorine, Chlorine, Bromine, and Iodine), the outer shell completes in a 4-hedron configuration except for Bromine, which has only a single electron in this shell. The added electron in F, Cl, and I completes the 4-hedron, while in Br, it doubles the rings within the 4-hedron.

The repulsion experienced by the added electron in F is due to the repulsion from three electron-rings, while in Cl, the repulsion is minimized due to the larger size and additional d orbital, making it easier to accept the electron. Similarly, in I and Br, the added electron completes or doubles the outer shell, respectively, leading to variations in the electron gain enthalpy values.