Formation of hydrogen Molecule

Formation of hydrogen (H2) Molecule

Electronic configuration of hydrogen atom is 1s1

During the formation of H2 molecule, the 1s orbitals of two hydrogen atoms containing one unpaired electron with opposite spin overlap with each other along the internuclear axis. This overlap is called s-s overlap. Such axial overlap results in the formation of a σ-covalent bond.

Formation of fluorine molecule (F2):

Valence shell electronic configuration of fluorine atom : 2s2 2px2, 2py2, 2pz1

When the half filled pz orbitals of two fluorine overlaps along the z-axis, a σ-covalent bond is formed between them.

Formation of HF molecule:

Electronic configuration of hydrogen atom is 1s1

Valence shell electronic configuration of fluorine atom : 2s2 2px2, 2py2, 2pz1

When half filled 1s orbital of hydrogen linearly overlaps with a half filled 2pz orbital of fluorine, a σ-covalent bond is formed between hydrogen and fluorine.

Formation of oxygen molecule (O2):

Valence shell electronic configuration of oxygen atom : 2s2 2px2, 2py1, 2pz1

When the half filled pz orbitals of two oxygen overlaps along the z-axis (considering molecular axis as z axis), a σ-covalent bond is formed between them. Other two half filled py orbitals of two oxygen atoms overlap laterally (sideways) to form a π-covalent bond between the oxygen atoms. Thus, in oxygen molecule, two oxygen atoms are connected by two covalent bonds (double bond). The other two pair of electrons present in the 2s and 2px orbital do not involve in bonding and remains as lone pairs on the respective oxygen.