Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The Pauling scale is the most commonly used. Fluorine (the most electronegative element) is assigned a value of 4.0, and values range down to caesium and francium which are the least electronegative at 0.7
What happens if two atoms of equal electronegativity bond together?
Consider a bond between two atoms, A and B. Each atom may be forming other bonds as well as the one shown - but these are irrelevant to the argument.
If the atoms are equally electronegative, both have the same tendency to attract the bonding pair of electrons, and so it will be found on average half way between the two atoms. To get a bond like this, A and B would usually have to be the same atom. You will find this sort of bond in, for example, H2 or Cl2molecules.
Electronegativity, symbol X, is a chemical property that describes the tendency of an atom or a functional group to attract electrons (or electron density) towards itself. An atom's electronegativity is affected by both its atomic number and the distance at which its valence electrons reside from the charged nucleus. The higher the associated electronegativity number, the more an element or compound attracts electrons towards it.
Factors affecting electronegativity
The Size of an Atom
A larger atomic size will result in less value of electronegativity. It happens because electrons being far away from the nucleus will experience a lesser force of attraction.
The Nuclear Charge
A larger value of nuclear charge will result in a greater value of electronegativity. It happens because an increase in nuclear charge causes electron attraction with greater force.
Effect of Substituent
The electronegativity of an atom depends on nature of the substituent attached to that atom. The difference in electronegativity of an atom caused by substituents results in different chemical behaviour of that atom.
Least Electronegative Elements
Cesium is the least electronegative element having electronegativity value is 0.79. Electro positivity is the exact opposite of electronegativity, means Cesium is the most electropositive element.
Most Electronegative Elements
Fluorine is the most electronegative element on the periodic table. Its electronegativity value is 3.98.