Covalent vs Polar Covalent
As proposed by the American chemist G.N.Lewis, atoms are stable when they contain eight electrons in their valence shell. Most of the atoms have less than eight electrons in their valence shells (except the noble gases in the group 18 of the periodic table); therefore, they are not stable. These atoms tend to react with each other, to become stable. Thus, each atom can achieve a noble gas electronic configuration. Covalent bonds are a major type of chemical bonds, which connect atoms in a chemical compound. There are two types of covalent bonds as non polar and polar covalent bonds.
Polarity arises due to the differences in electronegativity. Electronegativity gives a measurement of an atom to attract electrons in a bond. Usually Pauling scale is used to indicate the electronegativity values. In the periodic table, there is a pattern as to how the electronegativity values are changing. From left to right through a period, the electronegativity value increases. Therefore, halogens have larger electronegativity values in a period, and group 1 elements have comparatively low electronegativity values. Down the group, the electronegativity values decrease. 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 bonds is known as non polar covalent bonds.
When two atoms having similar or very low electronegativity difference, react together, they form a covalent bond by sharing electrons. Both atoms can obtain the noble gas electronic configuration by sharing electrons in this way. Molecule is the product resulted by the formation of covalent bonds between atoms. For example, when the same atoms are joined to form molecules like Cl2, H2, or P4, each atom is bonded to another by a covalent bond.
Depending on the degree of electronegativity difference, the covalent character can be changed. This degree of difference may be higher or lower. Therefore, the bond electron pair is pulled more by one atom compared to the other atom, which 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 covalent 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).
What is the difference between Covalent and Polar Covalent?
• Polar covalent bonds are a type of covalent bonds.
• Covalent bonds, which are non-polar, are made by two atoms with similar electronegativities. Polar covalent bonds are made by two atoms with different electronegativities (but the different shouldn’t be exceeding 1.7).
• In non polar covalent bonds, electrons are equally shared by the two atoms participating in making the bond. In polar covalent, electron pair is pulled more by one atom compared to the other atom. So the electron sharing is not equal.
• Polar covalent bond has a dipole moment, whereas a non polar covalent bond doesn’t.