Electronegativity Chart of Elements: Periodic Trend

The measure of an element's ability to attract a pair of bonding electrons towards itself is known as electronegativity. As per Linus Pauling, electronegativity is "the power of an atom in a molecule to attract electrons to itself." Hence, the relative value of an atom, with respect to its other bonding atom is called the electronegativity of that atom. The electronegativity chart shows the elements and their value in ascending order. 

Read Also : Periodic Classification

According to the electronegativity chart, if one atom is less electronegative than its counterpart, its electron density shifts, inching closer towards the more electronegative atom. For example, in a sequence where elements A and B are bonding together, and B is slightly less electronegative than A, then the electron pair will move towards A. turning it in a negative charge; whereas B will turn to acquire a positive charge.

Bond Between Two Atoms

Consider two atoms, A and B, with a tendency to attract bonding pairs of electrons, bond together. Here's how they would look with their respective electronegative values:

1. When the two atoms bonding together have equal electronegativity

           

2. When element B is slightly more electronegative than element A:

         

3. When element A is slightly more electronegative than element B:

        

Factors Affecting the Electronegativity of an Atom

Following are the factors that affect the electronegativity of an atom:
 

1. Hybridization: The state of hybridization influences to a great extent the electronegativity of that element. For instance, if a carbon atom sp, sp², and sp³ are hybridized in three compounds A, B, and C respectively, then, in these three compounds the order of electronegativity of carbon atom will be –

          sp> sp²> sp³

2. Oxidation state: It is the state that implies the number of electrons that an atom can lose, gain or share with another atom. This state of an element also influences its electronegativity. The electronegativity also increases as the oxidation state of elements increases.
3. Nature of Substituent Attached to the Atom: The carbon attached to more electronegative elements will possess a greater positive charge if a carbon atom is attached to more electronegative atoms while another is attached to less electronegative elements.

Determination of Electronegativity of an Element

There are numerous ways to determine electronegativity, namely the Mulliken electronegativity method, Alfred-Rochow electronegativity method, and the Pauling Scale. The most commonly used method is the Pauling Scale, named after American Chemist and lead researcher Linus Pauling, who developed a scale in 1932. Pauling's measurement scale is built on the findings of the Valence Bond Theory which entangle the relationship between different chemical properties. It is also based on the covalent bonds of different elements and their bond energy calculations. Linus Pauling used bond energies and experimental data to assess a mathematical equation, which helps in determining the electronegativity of an element.

As per Pauling's findings, Caesium, at 0.79, is the least electronegative element, whereas Fluorine, at 4.0, is the most electronegative element in the periodic table. 

It must be noted that the electronegativity of an element is dependent on the distinct properties of individual elements, and hence it can never be measured independently. Several methods to measure electronegativity have been introduced, produced almost similar numerical values and periodic trends.

Uses of the Measurement of Electronegativity Values

1. Electronegativity measurement is used to predict whether an atom will form a covalent bond or an ionic bond.
2. It is also used to predict whether the resultant molecule will take the form of polar or nonpolar. 

Electronegativity Chart and Electronegativity Trend in the Periodic Table

Most periodic tables display the electronegative values of individual elements that can be easily found, as they are placed adjacent to other properties. The electronegative trends reflect in the placement of the elements of the table. The electronegativity increases as we move from left to right, whereas there is a decline in the electronegative values as we read the table from top to bottom. Likewise, to read the chart, point towards the element fluorine, as the value increases in the lead up to the highest value element. 

Read more : Noble Gases

A periodic table can also be prepared in accordance with the electronegativity chart. Here's a periodic table reflecting Pauling's electronegativity scale.

Here is the Electronegativity Chart, depicting values of crucial elements:

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Things to Remember

• Electronegativity isn't just a property of an atom, it's actually the discovered property of an atom in a molecule.
• An atom's electronegativity has a strong correlation to its first ionization energy, meanwhile, it serves a negative correlation with the atom's electron affinity. 
• The electronegativity of an element varies according to the chemical environment it is in, but it comes under the rules of transferable property.
• The difference between the electronegativity bonds leads to the formation of bonds.
• When the difference between the electronegativity is small, a polar covalent bond is formed.
• When the difference between the electronegativity is large, an ionic bond is formed.