electronegativity indicates the tendency of an atom to attract a pair of electrons in a covalent bond, which occurs when this atom shares one or more pairs of electrons.
If two bonded atoms have the same electronegativity values, they share electrons equally in a covalent bond. However, usually the electrons in a chemical bond are more attracted to one atom (the most electronegative) than to the other.
If the electronegativity values are very different, the electrons will not be shared. An atom, in this case, monopolizes the bonding electrons of the other atom, forming an ionic bond.
Examples of electronegativity
An example of electronegativity is the Chlorine atom, which has a higher electronegativity than the Hydrogen atom. Therefore, the binding electrons will be closer to the Cl (chlorine) that from H (hydrogen) in the molecule of HCl (hydrochloric acid or hydrogen chloride).
Another example is what happens in the O2 (oxygen) molecule, where both atoms have the same electronegativity. That is, the electrons in the covalent bond are shared equally between the two oxygen atoms.
Electronegativity on the periodic table
It can be said that electronegativity is a periodic property that increases from left to right and from bottom to top on the Periodic Table.
Electronegativity and ionization energy follow the same trend as the periodic table, so elements that have low ionization energy tend to also have low electronegativity.
The nuclei of these atoms do not exert a strong attraction on electrons. Likewise, elements that have high ionization energies tend to have high electronegativity values, and the atomic nucleus exerts a strong influence on electrons.
Example of electronegativity in the periodic table, found in its greatest quantity in the elements from left to right.
The most electronegative element is the Fluorine (F) and the less electronegative (or more electropositive) elements are the francium (Fr) and the Cesium (Cs).
Noble gases, on the other hand, as they do not make chemical bonds, have zero or insignificant electronegativity.
Electronegativity Scale
THE Pauling scale is the most used to calculate electronegativity. It was created by Linus Pauling, who assigned the electronegativity of Fluorine as 4 and Francium as 0.7 and, then calculated the electronegativity of other elements between those numbers, using energies of Link.
However, when performing calculations on a wide range of compounds, an electronegativity of 3.98 is attributed to Fluorine. This is because this value gives better internal consistency.
Another scale is the Mulliken Scale, which bases the electronegativity values on the following equation: Electronegativity = 0.5 x (Ionization Potential + Electronic Affinity)
Electronegativity is a relative scale, that is, it is calculated and not measured.
Difference between electronegativity and electropositivity
In electronegativity, an atom can attract a shared pair of electrons in its combined state. In electropositivity, the atom can take out a shared pair of electrons in its combined state.
Note, then, that both are contradictory terms, that is, a more electronegative atom is, consequently, less electropositive and vice versa. Furthermore, these values depend on the atom to which it binds during covalent bonding.
See also the meaning of:
- Chemistry
- Linus Pauling diagram.