The key difference between electron affinity and electron gain enthalpy is that electron affinity refers to the tendency of an isolated atom to obtain an electron, whereas electron gain enthalpy is the energy released when an isolated neutral atom gains one extra electron.
Electron affinity and electron gain enthalpy are two related terms because electron gain enthalpy is a measurement regarding electron affinity.
CONTENTS
1. Overview and Key Difference
2. What is Electron Affinity
3. What is Electron Gain Enthalpy
4. Side by Side Comparison – Electron Affinity vs Electron Gain Enthalpy in Tabular Form
5. Summary
What is Electron Affinity?
Electron affinity is the amount of energy released when a neutral atom or a molecule (in the gaseous phase) gains an electron from the outside. This process of electron gaining can cause the formation of a negatively charged chemical species.
Furthermore, the addition of an electron to a neutral atom or a molecule releases energy. We can call this an exothermic reaction. This type of reaction results in a negative ion. However, if another electron is going to be added to this negative ion, energy should be given in order to proceed with that reaction. This is because the incoming electron is repelled by other electrons. This phenomenon is called an endothermic reaction.
The first electron affinities are negative values and the second electron affinity values of the same species are positive values.
Electron affinity shows a periodic variation in the periodic table. This is because the incoming electron is added to the outermost orbital of an atom. The elements of the periodic table are arranged according to the ascending order of their atomic number. When the atomic number increases, the number of electrons they have in their outermost orbitals increases.
In general, electron affinity should increase along the period from left to right because the number of electrons increases along a period; thus, it is difficult to add a new electron. When experimentally analyzed, the electron affinity values show a zig-zag pattern rather than a pattern that shows a gradual increase.
What is Electron Gain Enthalpy?
Electron gain enthalpy is the change in enthalpy when a neutral atom or a molecule gains an electron from outside. We can say it is the amount of energy released when a neutral atom or molecule (in the gaseous phase) gains an electron from the outside. Therefore, the electron gain enthalpy is another term that we use for electron affinity. The unit for the measurement of electron gain enthalpy is kJ/mol. The new electron addition causes the formation of a negatively charged chemical species.
However, there is a distinction between electron gain enthalpy and electron affinity. Electron gain enthalpy represents the energy released to the surrounding when an electron is gained, whereas electron affinity represents the energy absorbed by the surrounding when an electron is gained. Therefore, electron gain enthalpy is a negative value, while electron affinity is a positive value. Basically, both terms represent the same chemical process.
The electron gain enthalpy gives us an idea about how strong an electron is bound to an atom. Greater the amount of energy released, greater the electron gain enthalpy.
The value of the electron gain enthalpy depends on the electron configuration of the atom to which an electron is gained. The addition of an electron to a neutral atom or a molecule releases energy. This is called an exothermic reaction. This reaction results in a negative ion. Electron gain enthalpy will be a negative value. But if another electron is going to be added to this negative ion, energy should be given in order to proceed with that reaction. This is because the incoming electron is repelled by the other electrons. This phenomenon is called an endothermic reaction. Here, the electron gain enthalpy will be a positive value.
What is the Difference Between Electron Affinity and Electron Gain Enthalpy?
Electron affinity is the amount of energy released when a neutral atom or a molecule (in the gaseous phase) gains an electron from the outside. Electron gain enthalpy is the change in enthalpy when a neutral atom or a molecule gains an electron from outside. The key difference between electron affinity and electron gain enthalpy is that electron affinity refers to the tendency of an isolated atom to obtain an electron whereas electron gain enthalpy is the energy that releases when an isolated neutral atom gains one extra electron.
Below is a summary of the difference between electron affinity and electron gain enthalpy in tabular form.
Summary – Electron Affinity vs Electron Gain Enthalpy
Electron affinity and electron gain enthalpy are two related terms because electron gain enthalpy is a measurement regarding electron affinity. The key difference between electron affinity and electron gain enthalpy is that electron affinity refers to the tendency of an isolated atom to obtain an electron, whereas electron gain enthalpy is the energy that releases when an isolated neutral atom gains one extra electron.
Reference:
1. “Electron Affinity.” Chemistry LibreTexts, Libretexts, 26 Sept. 2020, Available here.
Image Courtesy:
1. “Electron affinity periodic table” By Cdang and Adrignola (CC BY-SA 3.0) via Commons Wikimedia