Fajan’s Rule
Fajan’s rule is postulated by Kazimierz Fajans in 1923. Fajans’ rule determines whether a chemical bond is covalent or ionic. He was able to predict ionic or covalent bonding at the time using X-ray crystallography and attributes such as ionic and atomic radius. The key points of Fajan’s rule are as follows:
- Polarizing Power: Fajan’s rule states that cations with a higher charge or smaller size have greater polarizing power. A cation with a higher charge density, resulting from a higher charge or smaller size, can pull the shared electrons in a bond closer to itself, creating a more polar bond.
- Polarizability: Fajan’s rule also considers the concept of polarizability, which refers to the ease with which the electron cloud of an atom or ion can be distorted. An anion with a larger size and more diffuse electron cloud is more easily polarized.
- Ionic Character: According to Fajan’s rule, a chemical bond between a cation and an anion with high polarizing power and high polarizability respectively exhibits a greater degree of ionic character. In other words, the electrons in the bond are more localized towards the cation, creating a polar covalent or even an ionic bond.
- Covalent Character: Conversely, a bond between species with low polarizing power and low polarizability tends to have a more covalent character. The electrons in the bond are more evenly shared between the atoms, resulting in a less polar or even nonpolar bond.
Examples of Fajan’s Rule
Some examples of Fajan’s Rule are as follows:
- Sodium chloride (NaCl) has a low polarizing power cation (Na+) and a small polarizability anion (Cl–). Therefore, NaCl has a high degree of ionic character.
- Magnesium oxide (MgO) has a high polarizing power cation (Mg2+) and a large polarizability anion (O2-). Therefore, MgO has a lower degree of ionic character and a higher degree of covalent character.
- Aluminum iodide (AlI3) has a very high polarizing power cation (Al3+) and a very large polarizability anion (I–). Therefore, AII3 has a very low degree of ionic character and a very high degree of covalent character.
Chemical Bonding
Chemical Bonding as the name suggests means the interaction of different elements or compounds which defines the properties of matter. Chemical bonds are formed when either at least one electron is lost to another atom, obtaining at least one electron from a different atom, or transferring one electron to another atom. In this article, we will learn about the theories of chemical bonding such as Lewis’s theory which explains the Lewis structure of any compound, Kossel’s Theory, and Fajan’s rule. So, let’s begin the journey of Chemical Bonding.
Contact Us