Lewis Theory | Chemical bonding of Lewis Theory |.
In 1916 W. Kossel and G.N. Lewis put forward the electronic theory of chemical bonding. It was suggested that in a chemical reaction, the atom of an element adjusts their electronic configuration to that of the nearest noble gas. The atoms acquire two electrons, duplet configuration, or eight electron octet structure. For example, H, Li, and Be acquire ns2, and all other atoms tend to attain ns2 np6 configuration. On the basis of this octet theory, the chemical bonds have been divided into the following three types:
- Ionic or Electrovalent Bond.
- Covalent Bond.
- Co-ordinate bond.
The bond formed by the complete transference of one or more electrons from one atom to another atom is called the ionic or electrovalent bond. This is formed between the elements of low ionization potential values (i.e., elements of group I-A and II-A) and the elements with a high electron affinity values such as the element of Group Vi and Vii-A.
- Sodium loses one electron to attain the electronic configuration of neon,1s², 2s², 2p⁶.
- Chlorine gains one electron to acquire the electronic configuration of argon ( 1s² 2s² 2p⁶ 3s² 2p⁶)
- The oppositely charged ions formed in this way are held together by the electrostatic force of attraction.
- Calcium loses two-electron to form Ca2+ ions and acquires electronic configuration of argon ( 1s² 2s² 2p⁶ 3s² 3p⁶)
- These two electrons are taken up by two chlorine atoms to form Cl− ions.
- Due to the electrostatic force of attraction, these ions pack themselves in a crystal lattice.
“A bond formed by the mutual sharing of electrons between two atoms is called Covalent Bond“. The atoms with zero or low electronegativity differences usually form covalent bonds.
Formation of H2:
- Two hydrogen atoms share their electrons and attain be a configuration of helium, (1s²)
- Two hydrogen atoms attain the configuration of Helium (1s²) and oxygen acquires Neon configuration (1s² 2s² 2p⁶), in the formation of H2O.
- Similarly, in the formation of NH3. each atom tends to acquire noble gas configuration
Coordinate covalent Bond.
“A covalent bond in which both in electrons are donated by one of the atoms is called Co-ordinate covalent bond. The atom which donates the electron pair is called the donor atom and the atom which accepts than for bond formation is called the acceptor. This bond is represented by an arrow that runs from donor to acceptor atom.
Formation of NH+4 :
- Lone pair electron of nitrogen is donated to H+ to form a Co-ordinate covalent bond.
Formation of H3O+:
- Lone pair of electron on oxygen forms a coordinate covalent bond with H+.