The key difference between electronegativity and polarity is that electronegativity is the tendency of an atom to attract the electrons in a bond towards it, whereas polarity means the separation of the charges.
Polarity arises due to the differences in electronegativity. Therefore, these two terms are closely related terms. However, there is a distinct difference between electronegativity and polarity. One such difference between electronegativity and polarity is that electronegativity describes the attraction forces at the atomic level while the polarity describes the attraction forces at the molecular level.
CONTENTS
1. Overview and Key Difference
2. What is Electronegativity
3. What is Polarity
4. Side by Side Comparison – Electronegativity vs Polarity in Tabular Form
5. Summary
What is Electronegativity?
Electronegativity is the tendency of an atom to attract the electrons in a bond towards it. Basically, this shows the “likeness” of an atom towards the electrons. We can use the Pauling scale 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. From top to bottom, on a group, electronegativity decreases. Therefore, fluorine is the most electronegative element with a value of 4.0 on 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.
Figure 01: Electronegativity of Elements in the Periodic Table
Electronegativity is also important in determining the nature of bonds. If the two atoms in the bond have no electronegativity difference, then a covalent bond will form. If the electronegativity difference between the two is high, then an ionic bond will form.
What is Polarity?
Polarity arises due to the differences in electronegativity of atoms. When two of the same atom or atoms having the same electronegativity form a bond between them, these 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 participating in making the bond. Thus, it will result in an unequal distribution of electrons between the two atoms. Moreover, 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 partial positive charge. The atom with a higher electronegativity gets the partial negative charge, and the atom with the lower electronegativity will get the partial positive charge. Polarity refers to the separation of the charges. These molecules have a dipole moment.
Figure 2: Charge Separation in C-F Bond; Fluorine is more Electronegative than Carbon
In a molecule, there can be at least one bond or more. Some bonds are polar while some are non-polar. For a molecule to be polar, all the bonds should collectively produce an uneven charge distribution within the molecule.
Polar Molecules
Furthermore, 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. The dipole moment in these molecules is permanent because they have arisen due to the electronegativity differences. But, there are other molecules that can be polar only on certain occasions. A molecule with a permanent dipole can induce a dipole in another non-polar molecule, then that will also become temporary polar molecules. Even within a molecule, certain changes may cause a temporary dipole moment.
What is the Difference Between Electronegativity and Polarity?
Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons while polarity is the property of having poles or being polar. So, the key difference between electronegativity and polarity is that the electronegativity is the tendency of an atom to attract the electrons in a bond towards it, whereas polarity is the separation of the charges.
Moreover, an additional difference between electronegativity and polarity is that the electronegativity describes the attraction forces at the atomic level while the polarity describes the attraction forces at the molecular level. Therefore, the attraction between the atomic nucleus and outermost electrons is the reason for an atom to have an electronegativity value; thus, it determines the value of electronegativity. But, polarity is caused by the separation of charges in a bond due to the differences in electronegativity values of atoms.
Below infographic shows more details on the difference between electronegativity and polarity.
Summary – Electronegativity vs Polarity
Electronegativity and polarity are related terms; the electronegativity of atoms in a molecule determines the polarity of the molecule. The key difference between electronegativity and polarity is that electronegativity is the tendency of an atom to attract the electrons in a bond towards it, whereas polarity means the separation of the charges.
Reference:
1. Helmenstine, Anne Marie. “Electronegativity Definition and Examples.” ThoughtCo, Oct. 17, 2018, Available here.
Image Courtesy:
1. “Periodic table Pauling electronegatvity” By DMacks – (CC BY-SA 3.0) via Commons Wikimedia
2. “Carbon-fluorine-bond-polarity-2D” By Ben Mills – Own work (Public Domain) via Commons Wikimedia