Electronegativity vs Polarity
Electronegativity is the tendency of an atom to attract the electrons in a bond towards it. Simply, this shows the “likeness” of an atom towards the electrons. Pauling scale is commonly used to indicate the electronegativity of elements. In the periodic table, electronegativity changes according to a pattern. From left to right, on a period, electronegativity increases. And from top to bottom, on a group, electronegativity decreases. Therefore, fluorine is the most electronegative element with the value of 4.0 in the Pauling scale. Group one and two elements have less electronegativity; thus, they tend to form positive ions by giving electrons. Since group 5, 6, 7 elements have a higher electronegativity value they like to take electrons in and from negative ions. Electronegativity is also important in determining the nature of bonds. If the two atoms in the bond have no electronegativity difference, then a pure covalent bond will result. If the electronegativity difference between the two is high, then an ionic bond will result.
Polarity arises due to the differences in electronegativity. When two of the same atom or atoms having the same electronegativity form a bond between them, those atoms pull the electron pair in a similar way. Therefore, they tend to share the electrons and this kind of nonpolar bonds is known as covalent bonds. However, when the two atoms are different, their electronegativities are often different. But the degree of difference may be higher or lower. Therefore, the bonded electron pair is pulled more by one atom compared to the other atom that is participating in making the bond. This will result in an unequal distribution of electrons between the two atoms. And these types of covalent bonds are known as polar bonds. Because of the uneven sharing of electrons, one atom will have a slightly negative charge whereas the other atom will have a slightly positive charge. At this instance, we say that the atoms have obtained a partial negative or positive charge. The atom with a higher electronegativity gets the slight negative charge, and the atom with a lower electronegativity will get the slight positive charge. Polarity means the separation of the charges. These molecules have a dipole moment. Dipole moment measures the polarity of a bond, and it is commonly measured in debyes (it also has a direction).
In a molecule, there can be at least one bond or more than that. Some bonds are polar, and some are non-polar. For a molecule to be polar, all the bonds collectively should produce an uneven charge distribution within the molecule. Further, molecules have different geometries, so the distribution of bonds also determines the polarity of the molecule. For example, hydrogen chloride is a polar molecule with only one bond. Water molecule is a polar molecule with two bonds. And ammonia is another polar molecule. The dipole moment in these molecules is permanent because they have arisen due to the electronegativity differences. But there are other molecules, which can be polar only in certain occasions. A molecule with a permanent dipole can induce a dipole in another non-polar molecule and then that will also become temporary polar molecules. Even within a molecule certain changes may cause a temporally dipole moment.
What is the difference between Electronegativity and Polarity?
• Electronegativity is the tendency of an atom to attract the electrons in a bond towards it. Polarity means the separation of the charges.
• Polarity arises due to the differences in electronegativity.
• Polarity also depends on the molecular shape, whereas it doesn’t affect for electronegativity.