Concept of Electronegativity

Introduction

Electronegativity reflects the net effect of the tendency of atoms to attract electron pairs in various elements. Several scales are used to measure electronegativity. Linus Pauling devised an electronegativity scale in 1932 that was commonly used to measure the electronegativity of chemical elements. It is most common to use the Pauling scale, but other scales are available, such as the Sanderson scale. This popularly known scale was developed from the Valence Bond Theory, which appeared to help Pauling understand how one chemical property was related to another. It was also based on the bond-energy calculation for various covalent bond elements. Fluorine has a value of 4.0, while cesium has a value of 0.7, making it the most and least electronegative element, respectively. 

Electronegativity definition is that the ability of atoms to attract electrons to themselves inside a molecule is called electronegativity. The electronegativity values of almost every element in the periodic table have already been determined theoretically or experimentally. The electronegativity of hydrogen is 2.20. Even though electronegativity had been studied and understood for years by chemists before 1811, Jöns Jacob Berzelius introduced the term. The atomic number and the distance between the charged nucleus and the valence electrons affect an atom’s electronegativity. Atomic sizes decrease, and nuclear charges increase across a period of the modern periodic table, increasing electronegativity. According to the modern periodic table, moving down each group increases the atomic number, and nuclear charge also increases, but the effect is mitigated if one shell is added. Thus, electronegativity values decrease downward with groups. For example, electronegativity values decrease from fluorine to astatine. An element’s electronegativity, however, cannot be measured directly since its unique characteristics determine it. Electricity serves two main purposes:

• An atom’s potential to form a covalent or an ionic bond.

• Predict the polarity or nonpolarity of the resultant molecule.

Example: Compared to hydrogen, chlorine has a higher electronegativity. Because of this, the bonding electrons are closer to the chlorine in the molecule of HCl. Both atoms in O2 have symmetric electronegativity.

Electro-positivity is the opposite of electronegativity, making cesium the most electropositive element. Electronegative elements are those with the fewest inner electron shells and require the fewest electrons to complete their valence shells. Fluorine has an electronegativity of 4.0, making it the most electronegative of all the elements. Cesium (Cs) and francium (Fr) are the least electronegative elements, both having electronegativity values of 0.7. In general, metals demonstrate a lower electronegativity compared to non-metals. As a result, metals are electropositive and non-metals are electronegative.

The electronegativity of two bonded atoms greatly impacts the covalent bond’s strength. Due to the electronegativity of bonded atoms being the same, homonuclear diatomic molecules have incredibly pure covalent bonds. Polarization occurs between species with different electronegativity. In chemical bonds, partial positive charges are formed when the more electropositive atom develops a partial charge. 

In addition to understanding that all covalent bonds between dissimilar species possess ionic character, all ionic bonds also possess some covalent properties. When there is little difference between the electronegativities of the bound species, a bond is covalent. When the electronegativity difference of two bonded atoms is greater then 1.7 then bond is described as ionic. As the electronegativity difference increases, polarization increases thus the compound should be polar.

There are various factors that affect electronegativity:

• Atom size: Atoms that are larger will have a lower electronegativity because electrons are further away from the nucleus and will thus be less attracted to it.

• Charge of nuclear: When the nuclear charge is higher, the electronegativity will be higher. As the nuclear charge increases, stronger electron attraction occurs.

• Substituent effect: An atom’s electronegativity is determined by the kind of substituent attached to it. As a result of substituents, an atom has a different electronegativity and behaves chemically differently.

Element’s electronegativity values are usually found in the periodic table. Fluorine electronegativity is the greatest in the periodic table. As the periodic table moves toward fluorine, the electronegativity value rises. In the Periodic table, we can also observe some electronegativity trends. Moving left to the right in the Periodic table increases electronegativity while moving top to bottom decreases it. Furthermore, you can also create the electronegativity chart according to the periodic table. 

Other calculation methods

• Pauling Electronegativity: Originally, electronegativity was described by Linus Pauling. In Pauling’s definition, electronegativity is an atom’s ability to attract electrons. The higher an element’s electronegativity, the more those atoms attempt to pull electrons toward themselves and away from other atoms they bond with.

• Mulliken Electronegativity: According to Mulliken, an atom’s tendency to attract electrons should be measured by the arithmetic mean of its first ionization energy plus its electron affinity. Mulliken electronegativity is sometimes mentioned as being the negative of chemical potential.

• Allred-Rochow Electronegativity: The charge an electron encounters on the surface of an atom is what causes electronegativity, according to both of them. The presence of a large charge on an atom’s surface increases its ability to attract electrons.

• Sanderson Electronegativity: A connection between Mulliken electronegativity and atomic size was observed by Sanderson. He proposed a reciprocal calculation of atomic volume as a method for calculating it. With Sanderson’s model, bond energies for a wide variety of compounds can be calculated with the knowledge of bond lengths.

• Allen Electronegativity: By Leland C. Allen, electronegativity is defined as the valence electron’s average energy in a free atom. This is perhaps the most straightforward and straightforward definition.

Conclusion:

As opposed to being a property of atoms by themselves, electronegativity is a property of atoms within molecules. An atom’s electronegativity is determined by its environment. Generally, an atom behaves the same way no matter its situation. Numerous factors influence electronegativity, including nuclear charges and the number and location of atom electrons. Atoms with a greater electronegativity difference form chemical bonds that are more polar. Fluorine is the most electronegative element compared to francium, which is the least electronegative element.