Electronegativity

Electronegativity is a measure of the extent to which an atom attracts electrons towards itself. It is one of the factors that causes molecules of different elements to combine.

A molecule is known as a group of two or more atoms held together by forces called chemical bonds. Chemical bonds are the result of electrons being shared between two or more atoms and causing them to attract each other. The stronger the attraction between the atoms, the stronger the bond. In general, covalent bonds form when there is little difference in electronegativities and ionic bonds form when there is a large difference in electronegativities.

The Pauling scale was devised by American chemist Linus Pauling in 1932 as a way of grading electronegativities from 0 (the least electronegative) to 4 (the most electronegative). It is an important property of a molecule that it contains the maximum possible number of covalent bonds. It also has an electronegative atom situated in the middle so that other atoms feel a strong pull towards it and thereby avoid forming covalent bonds with each other.

Periodic Trends

The value of electronegativity can be considered, to some degree, as a measure of how strongly the electrons in an atom are attracted to the protons in the nucleus. The bigger the number, the smaller the radius of the electron cloud surrounding the nucleus, and therefore, the stronger they are attracted to it.

The main trend is that as we move across a period of elements in a modern periodic table from left to right, the nuclear charge increases and therefore so does the strength with which electrons are attracted to protons. For example, across period 3 in the periodic table above, this trend appears by comparing two adjacent elements: boron and aluminum. As we move from left to right along this period (from boron to aluminum) the value of electronegativity increases:

Boron has an electronegativity value of 1.9

Aluminum has an electronegativity value of 2.5

This increase can be explained by considering that as we move from left to right along period 3 from boron to aluminum, one proton has been added to each nucleus [note 1]. This means that each time an extra proton has been added to a nucleus, it attracts one more electron (i.e. increases). 

Most and Least Electronegative elements

The periodic table has been established in such a way that the elements are arranged in order from left to right based on their electronegativity value. The elements with higher electronegativity values are placed before those with lower electronegativity values.  These elements have a positive value for electronegativity: H, Li, Na, K, Rb, Cs, F, Cl and Br. These elements have a negative value for electronegativity: He, Be, B, Al, Ga, In, Tl and Pb.

Electronegativity is the tendency of an atom in a molecule to attract electrons. The higher the electronegativity of an element, the more negative its charge. Electronegativity can be determined by dividing the atomic weight of an element by its valence electrons.

To compare elements we use a scale known as Pauling’s scale, in which oxygen has a value of 4.0 and fluorine has 3.98.

Fluorine is known as the most electronegative element on the periodic table. Its electronegativity value is 3.98. Cesium is known as  the least electronegative element. Its electronegativity value is 0.79. Electro positivity is the exact opposite of electronegativity, therefore, we can say that Cesium is the most electropositive element.

How does it affect Covalent bonds? 

The strength of a covalent bond is reliant upon the electronegativity of its atoms. A covalent bond is one in which the electrons are being shared by two atoms, as opposed to an ionic bond in which the electrons are being held in place by electrostatic attraction towards a particular atom. The strength of a covalent bond is highly dependent on the electronegativities of the two bonded atoms (especially their difference) and also on how far apart they are.

The term “electronegativity” is used to describe how strongly one atom can attract electrons from other atoms when it forms a chemical bond. In this way, electronegativity depends on how willing an atom is to share or donate its electrons in a bond. The more willing it is, the higher its electronegativity and therefore the stronger its bonds will be.

Homonuclear diatomic molecules feature relatively ‘pure’ covalent bonds since the electronegativities of both bonded atoms are purely the same (resulting in the bonded pair of electrons being almost equidistant from both bonded nuclei). Examples of such covalent bonds can be seen in H2 molecules, Cl2 molecules, and O2 molecules.

Electronegativity Table

Electronegativity is a nuclear property of an atom that indicates the power of that atom to attract electrons toward itself. When atoms are bonded together in molecules, the sharing of electrons is unequal, thus giving the molecule a net charge. Electronegativity is a scale that compares how much more strongly one element attracts electrons than another element does. This scale runs from about 0.7 for hydrogen (H), the least electronegative element, to about 4.0 for fluorine (F), the most electronegative element.

Electronegativity is an important factor in determining the strength and polarity of chemical bonds between atoms. The higher an atom’s electronegativity, the more likely it will attract bonding electrons from other atoms with which it forms a bond. This means that electronegativity is an important factor in determining whether an atom will have a metallic or covalent character in its compounds. It is also used to determine whether one atom will be oxidized or reduced when two different species come together during a redox reaction.

Tungsten, for example, has an electronegativity of 5.5 while carbon’s is 2.5. Because they have similar size and shape, both elements often find themselves living in the same chemical environment. If you compare tungsten and carbon at their respective positions in the periodic table (element 40 and 6), you’ll notice that tungsten has five times as many electrons in its outer shell as does carbon. Tungsten can pull them all into a single covalent bond (a shared pair of electrons), while carbon must use two covalent bonds to do so (a shared pair and another lone electron). 

Conclusion

In this material, we discussed the concept of electronegativity and how it was developed. Along with that, we also discussed the electronegativity table and which elements are the most and least electronegative