[Chemistry Class Notes] on Electronegativity Chart Pdf for Exam

Wondering what keeps the water in its form? Well, it is the bonding between hydrogen and oxygen that forms the water. This bonding which is highly affected by electronegativity is something that holds it together. Oxygen with its high electronegativity and hydrogen with its high electropositivity tends to hold each other together resulting in the formation of water.

Electronegativity is one of the important properties of an element or atom as it gives information about the binding nature of an element or atom. 

 

What is Electronegativity? 

Electronegativity is the measure of an element’s ability to attract a bonding pair of electrons towards itself. It was first described by Linus Pauling. Pauling defined electronegativity as “the power of an atom in a molecule to attract electrons to itself.” Thus, we can say the electronegativity of an atom is of relative value concerning that other atom to which it is bonded. If two atoms are bonded together and one atom is more electronegative than another bonded atom, then the electron density of the bond will shift slightly towards the more electronegative atom. 

 

For example, if two atoms or elements A and B are bonded together and A is slightly more electronegative than B then the electron pair will slightly shift towards A and it will get a slightly negative charge( Aδ-)while B will get a slightly positive charge( Bδ+).      

                                                 

These types of bonds are called polar bonds or polar covalent bonds. If the electronegativity of both elements A and B are equal, then they form a normal shared covalent bond. While if the electronegativity difference is too high between A and B then A being more electronegative than B dragged the electron pair towards itself completely and has complete control of both electrons. A gets a negative charge while B gets a positive and irons are formed. In this way, ionic bonds are formed between them. 

 

Examples – In water molecules, oxygen is more electronegative than hydrogen. So, oxygen pulls bonded electrons towards itself and gets a slightly negative charge while both hydrogen atoms get a slightly positive charge. The electronegativity value of oxygen is 3.5 while hydrogen is 2.1. 

 

Another example is carbon tetrachloride. Carbon is less electronegative than chlorine. So, they form polar bonds between them. Shared electron pairs shift towards chlorine. 

 

Factors Affecting Electronegativity of an Atom (Element)

The electronegativity of an element depends upon the following factors –

• Hybridization – The state of hybridization affects the electronegativity of that element. For example, if a carbon atom is sp, sp2 and sp3 hybridized in three compounds A, B and C respectively then the order of electronegativity of carbon atom in these three compounds will be – sp> sp2> sp3

• Oxidation state – It is the number of electrons that an atom can lose, gain or share with another atom. The oxidation state of an element also affects its electronegativity. As the oxidation state of elements increases, their electronegativity also increases. 

• Nature of Substituent Attached to the Atom – If a carbon atom is attached to more electronegative atoms while another is attached to less electronegative elements then the carbon attached to more electronegative elements will have a greater positive charge. For example, carbon atoms in CF3I possess a greater positive charge than carbon atoms of CH3I.  

 

Determination of Electronegativity of an Element 

The Pauling scale is most commonly used for the determination of the electronegativity of elements. It was named after Linus Pauling who first defined electronegativity. He used experimental data and bond energies to define a mathematical equation to determine the electronegativity of elements. He stated that fluorine is the most electronegative element in the periodic table. He assigned it a value of 4.0. while 0.79 to caesium which is the least electronegative element in the periodic table. 

 

Other methods to determine electronegativity of elements are the Mulliken electronegativity method, Allred – Rochow electronegativity method etc. 

 

Electronegativity Chart and Electronegativity Trend in Periodic Table 

We are giving here electronegativity of all important elements concerning your Class XII examinations for your better understanding of compounds of these elements. 

 

 

Fluorine is the most and Cesium is the least electronegative element in the periodic table. So, in groups and periods electronegativity always increases towards fluorine. 

 

Let’s discuss its trend across a period and a group in detail –

 

Electronegativity Trend Across a Period – As we move across a period electronegativity increases. The graph below shows electronegativities from sodium to chlorine which is increasing. We didn’t include argon as it is an inert gas and don’t form bonds with other elements. 

 

Electronegativity Trend Across a Group – As we move down across a group, electronegativity decreases. While going up across a period electronegativity increases.

 

Electronegativity trends in transition metals

Even after researching and learning about the electronegativity trends seen in transition metals, it is not so clear as to what they consist of. These are the elements that are present in the periodic table that consist of the most notable gold which is an inert metal. These metals are also known for the sea of electrons they consist of and hence the idea of pulling the electrons from other atoms does not seem like valid reasoning. Electronegativity can hence be best explained for the s block metals and the nonmetals that are present excluding the noble gases.

The article is helpful for students to understand the trends of electronegativity in the periodic tables. This is all about the electronegativity chart.