Electron Affinity: Factors Affecting, Halogens, Periodic Trends, Metals and Non-Metals, Highest and Lowest

Electron Affinity Overview

While forming an anion from a neutral atom, energy is released. The electron affinity changes when one electron transfers to a neutral gaseous atom to produce a negative ion. As a result, negative electron affinity promotes electron addition. Because not all elements produce stable negative ions, electron affinity is either zero or positive.

What is an Electron?

The electron is a subatomic particle with an initial electric charge of -1. Electrons are the first generation of the lepton particle family and are often regarded as elementary particles due to the lack of known components or substructure.

What is Electron Affinity?

The definition of electron affinity is When an electron is added to a neutral atom to create an anion, energy is released. When an electron is added to a neutral gaseous atom to generate a negative ion, the potential energy shift of the atom is measured. As a result, the more negative the electron affinity, the more advantageous the electron addition process. Because not all elements produce stable negative ions, their electron affinity is either zero or even positive.

Examples of Electron Affinity 

When a fluorine atom obtains an electron in the gaseous state to create F(g), the related energy change is -328 kJ/mol.

Molecular Electron Affinity

Molecule electron affinity is a complex function of their electrical structure. For example, the electron affinity of benzene and naphthalene is negative, but that of anthracene, phenanthrene, and pyrene is positive. In silico investigations reveal that hexacyanobenzene has a higher electron affinity than fullerene.

Factors Affecting Electron Affinity

1. Electron Affinity = 1/Atomic Size.
2. Electron Affinity = Effective Nuclear Charge.
3. Electron Affinity = 1/Screening Effect.
4. Reactivity of non-metals = Electron Affinity.
5. The oxidizing power of element Electron Affinity.

Three major factors influence electron affinity. These characteristics are often connected to the molecule's structure and arrangement. Nuclear Charge, Atomic Size, and Electronic Configuration are the three parameters that influence a molecule's electron affinity. The following are some of the factors affecting Electron Affinity-

1. Atomic Size: The larger the atom, the greater the distance between the nucleus and the electron. This will result in a lower electron attraction force. As a result, the value of electron affinity will be low. In general, electrical affinity grows as one moves down the group and diminishes as one moves left to right across the periods.
2. Electronic Arrangement: The more stable an atom's arrangement, the less likely it is to take an electron. As a result, its electron affinity will be reduced. In stable electrical configuration elements, electron affinity is almost nil or low. This is owing to the little proclivity to accept another electron. Inert gases have no electron affinities. This is because the atoms in their shell have a stable ns2np6 conformation. Beryllium and calcium have almost little electron affinity. If the atom's orbits are fully or partially filled, its electron affinity will be lower.
3. Nuclear Charge: The larger the nuclear charge, the stronger the incoming electron's attraction. This will result in a higher electron affinity value. To put it another way, the nuclear charge is the attraction that the nucleus has on the electrons. As a result, the stronger the nucleus' attraction, the more likely electrons will bind to the atom.

Because they have full electrons in their valence shells, Be and N have approximately 0 electron affinity. Because of symmetry, all filled orbits are stable. As a result, these elements will have the least proclivity to take any electron. In general, electron affinity follows the following pattern-

1. Halogens
2. Oxygen family 
3. Carbon family
4. Nitrogen family
5. Metals of group 1 and 13
6. Metals of group 2.

Electron Affinity of Halogens

The energy required to remove a gaseous electron is referred to as the ionization potential. Adding an electron generates energy, whereas subtracting one generates energy. The energy created when a gaseous neutral atom takes an electron and forms a negatively charged ion is known as electron affinity. When the first electron is added to an atom, a monovalent anion is formed, which releases energy. The addition of another electron to this anion repels it and absorbs energy. Additional electron affinities are positive.

Periodic Trends for Electron Affinity

The amount of energy released when an electron is added to a neutral atom to produce an anion is referred to as electron affinity. Electron affinities are difficult to quantify. Over time, electron affinity shifts from left to right. The general trend is caused by growing nuclear attraction over time. The electron affinity should decrease as one proceeds down the group since the electron is introduced more away from the atom. Less firmly bonded, and hence closer in energy to a free electron. 

1/Atomic Size = Electron Affinity

The electron affinity is derived indirectly rather than directly via the Born-Haber cycle.

The atomic size shrinks as we travel from left to right over time due to an increase in the nuclear force, and therefore the electron gain enthalpy rises. Moving down the periodic table increases atomic size, resulting in a drop in the value of electron gain enthalpy. 

First Electron Affinity

First, obtaining one electron to form 1 mole of gaseous -1 ions releases energy. This modification generates (per mole of X) energy. First, negative electron affinities. The electron affinity of chlorine is -349 kJ mol-1. Negative indications signify the discharge of energy. Adding an electron to metal necessitates the use of energy (endothermic process). Metals lose valance electrons and make cations faster than they receive electrons. Because the nuclei of metals do not exert a strong pull on their valence electrons, they are easily lost. Metals also have lower electron affinities.

Patterns in Electron Affinity

When electrons are added to energy levels, they migrate closer to the nucleus, and electron affinity rises higher for groups and from left to right across periods on a periodic table. Because greater distance results in less attraction, adding an electron to the outer orbital releases less energy. More valence electrons increase the likelihood of establishing a stable octet. With fewer valence electrons, there are fewer electron gains. Electron affinity decreases across groups and from right to left over time because electrons are positioned at a higher energy level away from the nucleus, lowering its attraction.

Metals and Non-Metals Electron Affinity

Metals tend to shed valence electrons in order to form cations, resulting in a fully stable octet. In order to shed electrons, they consume energy (are endothermic). Nonmetals have a greater affinity for electrons than metals. Nonmetals prefer to acquire electrons and produce anions in order to have a fully stable octet. Nonmetals have a greater electron affinity than metals because they expel energy (exothermic) in order to acquire electrons and form an anion.

Read more about the Reactivity Series of Metals.

Highest and Lowest Electron Affinity

Among the elements, chlorine has the highest electron affinity, because of its huge atomic radius (or size). Because the outermost orbital of chlorine is 3p, its electrons have a lot of area to share with an incoming electron. This reduces repulsions between these particles to a degree that balances the disadvantages of their size in terms of attraction.  Mercury has the lowest electron affinity. This status is due to its classification as a metal. In their search for a full, stable octet, metals are more prone to lose electrons than acquire them. Mercury's atomic radius is relatively big, which adds to its low value.

Sample Questions Related to Electron Affinity

Sample Question 1: Why are atoms with low electron affinities more prone to lose than gain electrons? 

Solution: Because they are further away from the nucleus, atoms with a low electron affinity desire to give up their valence electrons; as a result, they do not have a significant pull on the valence electrons.

Sample Question 2: Why is the electron affinity of noble gases positive? 

Solution: Because halogens may attain the closest stable noble gas configuration by absorbing an additional electron, their enthalpy of electron gain is substantially negative. In electron gain, noble gases have a substantial positive enthalpy.

Sample Question 3: What is the current state of electron affinity? 

Solution: Electron affinity increases from left to right and throughout periods of a periodic table because electrons added to energy levels go closer to the nucleus, making the nucleus and its electrons more appealing.

Sample Question 4: Is energy released or absorbed when an electron is introduced to a nonmetal atom? 

Solution: Energy is released when an electron is inserted into a nonmetal.

Sample Question 5: Why do nonmetal atoms have higher electron affinities than metal ones?

Solution: Because their atomic structure permits them to receive electrons rather than lose them, nonmetals have a higher electron affinity than metals.

Sample Question 6: What exactly is Electron Affinity? 

Solution: The change in energy (in kJ/mol) of a neutral atom (in the gaseous phase) when one electron is added to produce a negative ion is described as electron affinity.