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Understanding Electron Affinity: Definition, Factors & Periodic Trends
IMPORTANT LINKS
Classification of Elements and Periodicity in Properties
Understanding Electron Affinity
The term 'Electron Affinity' refers to
The energy change that occurs when an electron is added to a neutral atom, forming a negative ion.
Electron affinity represents the potential energy change of an atom when an electron is attached to a neutral gaseous atom to create a negative ion. Thus, the more negative the electron affinity, the more favorable the electron addition process becomes. However, not all elements form stable negative ions, so in such cases, the electron affinity could be zero or even positive.
Periodic Trends
Electron affinity is the energy released when an electron is added to a neutral atom to form a negative ion. Measuring electron affinities can be complex.
- Electron affinity tends to increase from left to right across a period due to increased nuclear attraction.
- As we move down a group, the electron affinity usually decreases because the electron is being added further away from the nucleus. The electron becomes less tightly bound and can be easily removed.
As we move from left to right in a period, the atomic size decreases due to an increase in nuclear force, hence the electron gain enthalpy increases. Conversely, while moving down a group in the periodic table, the atomic size increases, causing a decrease in the value of electron gain enthalpy .
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Factors Affecting Electron Affinity
Here are some key factors that can affect electron affinity.
Electron Affinity of Halogens
The Ionization potential is the energy required to remove an electron from a gaseous atom. When an extra electron is added to the atom, energy is released. This energy release when a neutral atom in its gaseous state accepts an electron and transforms into a negatively charged ion is known as electron affinity.
Here, X represents any element in the gaseous state and E.A. stands for the electron affinity. The electron affinity is usually represented in electron volts per atom or kilojoule per mole. For instance,
Hence, the electron affinity of chlorine is – 349 KJ/mol.
The energy release when the first electron is added to an atom, forming a monovalent anion, is known as the first electron affinity. However, adding another electron to this anion requires energy due to electron repulsion, making the second and further affinities positive in nature.
Frequently Asked Questions
What is the trend for electron affinity?
Electron Affinity increases across a period from left to right because of increasing effective nuclear charge and decreasing size of atoms. Electron Affinity decreases down the group due to increased size of atoms
Is electron affinity positive or negative?
When an electron is added to a neutral atom, energy is released and Electron Affinity is generally exothermic. Due to electronic repulsions, the second Electron Affinity can be positive
Who discovered the concept of electron affinity?
Electron Affinity was a concept that was discovered in 1901 in view of the discovery of electron negativity by Linus Carl Pauling. Electron Affinity is the amount of change in energy when an electron in a gaseous state is applied to a neutral atom.
Why is the electron affinity of noble gases positive?
The enthalpy of electron gain for halogens is highly negative because by accepting an extra electron they can acquire the nearest stable noble gas configuration. Noble gases have significant positive enthalpy in the gain of electrons.
Why do halogens have high electron affinity?
The halogens’ high electron affinities are due to their small size, high effective nuclear charge and an almost full outer shell of electrons. When an electron is added to halogens with very high electron affinity, high energy is released