UNIT 4 CHEMICAL BONDING AND MOLECULAR STRUCTURE
IONIC OR ELECTROVALENT BOND
The bond formed, as a result of the electrostatic attraction between the positive and negative ions was termed as the electrovalent bond. The formation of ionic compounds primarily depends on:
Lattice enthalpy: The lattice enthalpy of an ionic solid is defined as the energy required to completely separate one mole of a solid ionic compound into gaseous constituent.
THE VALENCE SHELL ELECTRON PAIR REPULSION (VSEPR) THEORY
The main postulates of the VSEPR theory are:
VALENCE BOND THEORY
VBT discusses bond formation in terms of overlap of orbitals. Because of orbital overlap the electron density between the nuclei increases which helps in bringing them closer. However, the actual bond enthalpy and bond length values are not obtained by overlap alone and other variables have to be taken into account.
Molecular Orbital Theory
The MO theory describes bonding in terms of the combination and arrangement of atomic orbitals to form molecular orbitals that are associated with the molecule as a whole. The number of molecular orbitals is always equal to the number of atomic orbitals from which they are formed. Bonding molecular orbitals increase electron density between the nuclei and are lower in energy than the individual atomic orbitals. Anti-bonding molecular orbitals have a region of zero electron density between the nuclei and have more energy than the individual atomic orbitals.