Electrons are subatomic particles that are present everywhere. As they have no components or substructure, they are considered to be elementary particles as a whole. This is why they exhibit properties of particles as well as waves.
The electrons have an essential part to play in several physical, chemical, them and electrical phenomena. They are the primary reasons why chemical reactions take place. Since an electron is a charged particle, it can absorb or release energy, which happens in most of the reactions mainly.
Two such chemical properties which require the involvement of electrons for showcasing the behaviour are Electronegativity and Electron Affinity. Both these properties are associated with electron gain and are correlated. Electronegativity is qualitative, whereas, electron affinity is quantitative.
Electron affinity is a property that an atom in a molecule exhibit, but electronegativity is the property of an atom which has formed bonds with any other atoms. Presence of electrons is the most essential part of these chemical properties that various elements exhibit. On the periodic table, these two properties increase across the periods and decrease down the groups.
Electronegativity vs Electron Affinity
The difference between Electronegativity and Electron Affinity is that Electronegativity is a property that shows the ability of an atom to attract or gain electrons in a chemical bonding, whereas, Electron Affinity is the measure of the amount of energy discharged or emitted when an electron gets added to an atom.
Comparison Table Between Electronegativity and Electron Affinity
| Parameter of Comparison | Electronegativity | Electro Affinity |
| Definition | The property of an atom to attract electrons towards it. | The property that refers to the discharge of energy when an electron is added to an atom. |
| Standard Unit | It is measured in Pauling. | While it is measured in KJ per mole. |
| Nature | This property is qualitative in nature. | Whereas this property is quantitative. |
| Associating Atom | The atom associated with it is a bonded atom. | Here, the atom associated is attached to a molecule or is neutral. |
| Highest Value | The highest value is obtained when the attracting energy is high. | While, in this case, the highest value is obtained when the nuclear charge is more. |
| Factors | Atomic number and distance between the valence electrons and the charged nucleus are the factors that affect electronegativity. | Atomic size, Nuclear charge and Electronic Configuration of the atoms are the factors that affect electron affinity. |
| Elements | Fluorine is the most electronegative element, while Francium is the least electronegative. | Chlorine is the one having the highest electron affinity, while Neon has the lowest. |
What is Electronegativity?
In 1811, Jöns Jacob Berzelius first introduced the term “electronegativity”. But after many more discoveries and discussions, it was only in 1932 that the property of electronegativity was fully discovered by Linus Pauling when he created an electronegative scale depending on bond enthalpies. This further aided the discovery of Valence Bond Theory.
The chemical property of an atom to attract a shared pair of electrons towards it is called electronegativity. In simple words, electronegativity is the ability of an atom to gain electrons. It is denoted by X and ranges from 0.79 to 3.98 on a scale. It is measured in Pauling.
The more the atomic number, the more the distance between the nucleus and the valence electrons and the more the electronegativity. So, the atomic number and location of electrons from the nucleus are the main factors affecting electronegativity. Also, the attraction tendency of the atom on electrons increases with an increase in the number of protons, i.e., the nuclear charge.
When two atoms having electronegativity are taken, an increasing difference between the electronegativity of the atoms will result in an increasing polar bond between them, with the atom with higher electronegativity at the negative end.
On a relative scale, electronegativity increases along a period from left to right and decreases on passing through a group. According to this, Fluorine is the most electronegative element and Francium is the least electronegative element.
What is Electron Affinity?
Electron Affinity is the measure of the amount of energy discharge that takes place when an electron gets added to an atom in a molecule or a neutral atom in the gaseous state, which then forms a negative ion. This property is donated by “Eea” and is measured in Kilo Joule (KJ) per mole.
Size of the atoms, i.e., atomic size, nuclear change and the electronic configuration of the molecule or atoms are the factors that determine the electron affinity of an atom or an element. An atom or molecule with a greater positive electron affinity value is referred to as an electron acceptor, while the one with a lower positive value is referred to as an electron donor.
The property of electron affinity is only used in the case of atoms and molecules present in the gaseous state only as the energy levels of the atoms present in the solid and liquid states get changed when they come in contact with other atoms or molecules.
Robert S. Mulliken used a bunch of the electron affinities of elements for developing the electronegativity scale. Other concepts such as chemical hardness and chemical potential also involve the theory of electron affinity in them.
Just like electronegativity, the electron affinity increases when passing through the periods and decrease down the groups. Based on this, Chlorine has the highest value of electron affinity and Neon has the lowest value of electron affinity.
Main Differences Between Electronegativity and Electron Affinity
- Electronegativity is the electron gain ability of atoms, while Electron affinity is the energy emitted during that.
- Electronegativity is a qualitative property, while Electron affinity is quantitative.
- In electronegativity, bonded atoms are involved but in electron affinity, atoms are neutral or in a molecule.
- One is measured in Pauling, other in KJ/mole.
- Atomic number and distance affect electronegativity; atomic size, nuclear charge and configuration affect electron affinity.
Conclusion
The property of electronegativity and electron affinity, both deal with the concept of electron gain. While electron affinity is capable of precise measurement and definition, electronegativity is capable of neither of them. As a result, the former is present in neutral atoms or atoms in a molecule and the latter deals with chemically bonded atoms.
References
https://pubs.acs.org/doi/pdf/10.1021/cr50004a005
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