Chemistry glossary Definition of electronegativity trend and examples
Electronegativity is the property of an atom which increases with its tendency to attract electrons from a bond . If two linked atoms have the same electronegativity values, they also share electrons in a covalent bond. However, usually the electrons in a chemical bond are more attracted to one atom (the more electronegative) than the other. This results in a polar covalent bond.
If the electronegativity values are very different, the electrons are not shared at all. One atom essentially takes the binding electrons from the other atom, forming an ionic bond.
Avogadro and other chemists studied electronegativity before being formally appointed by Jöns Jacob Berzelius in 1811. In 1932, Linus Pauling proposed a scale of electronegativity based on the energies of bonds. The electronegativity values on the Pauling scale are dimensionless numbers ranging from about 0.7 to 3.98. The values of the Pauling scale relate to the electronegativity of hydrogen (2.20). Although the Pauling scale is most often used, other scales include the Mulliken scale, the Allred-Rochow scale, the Allen scale and the Sanderson scale.
Electronegativity is a property of an atom in a molecule rather than an inherent property of an atom by itself. Thus, electronegativity actually varies depending on the environment of an atom. However, most of the time, an atom exhibits similar behavior in different situations.
Factors that affect electronegativity include the nuclear charge and the number and location of electrons in an atom.
Example of electronegativity
The atom chlorine has a higher electronegativity than the atoms of hydrogen , so that the electron binding will be closer than H Cl of the molecule HCl.
In the O 2 molecule , the two atoms have the same electronegativity. The electrons in the covalent bond are shared equally between the two oxygen atoms.
Most and least electronegative elements
The element the more electronegative on the periodic table is fluorine (3.98). The least electronegative element is cesium (0.79). The opposite of electronegativity is electropositivity, so you could just say that cesium is the most electropositive element. Note that older texts indicate both francium and cesium as the least electronegative (0.7), but the value for cesium has been experimentally revised to 0.79. There is no experimental data for francium, but its ionization energy is higher than that of cesium, so francium is expected to be slightly more electronegative.
Electronegativity as a trend of the periodic table
Like electron affinity, atomic / ionic radius and ionization energy, electronegativity shows a trend defined on the periodic table .
- Electronegativity generally increases from left to right over a period of time. Rare gases tend to be exceptions to this trend.
- The electronegativity generally decreases by descending from a group of periodic tables. This is correlated with the increase in the distance between the nucleus and the valence electron.
The electronegativity and the ionization energy follow the same tendency of the periodic table. Elements that have low ionization energies tend to have low electronegativity. The nuclei of these atoms do not exert a strong traction on the electrons. Likewise, elements which have high ionization energies tend to have high electronegativity values. The atomic nucleus exerts a strong traction on the electrons.
You may also look at
You may also look through