The electronegativity of an element refers to the tendency of an atom of that element to attract a shared pair of electrons towards itself. It is affected by the atomic number of the element and also by the distance between the nucleus of the atom and its valence shell. Electronegativity can be considered the root cause of several phenomena. The inductive effect, which arises due to the difference in the electronegativities of chemically bonded atoms, can lead to the formation of a permanent dipole within the molecule.
The opposite of electronegativity is electropositivity, which refers to the tendency of an atom to donate electrons. In the periodic table of elements, the electronegativity of the elements generally increases from left to right along a period and decreases while traversing downward through a group. The most electronegative element is fluorine and the least electronegative (or most electropositive) element is cesium.
It is important to note that the electronegativity is the property of an atom in a molecule. Therefore, the electronegativity of an element can vary with different chemical environments. However, it is often calculated as a dimensionless quantity with the help of the Pauling scale. This scale ranges from the values 0.79 (cesium) and 3.98 (fluorine). The electronegativity of hydrogen on the Pauling scale is 2.2.
When predicting the shapes of molecules with the help of the VSEPR theory, the least electronegative atom must be selected as the central atom. This is because the electropositivity of the central atom enables it to share its electrons with the other atoms in the molecule.
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