Sigma bonds are the strongest type of covalent bonds due to the direct overlap of orbitals, and the electrons in these bonds are sometimes referred to as sigma electrons.The symbol σ is the Greek letter sigma. The corresponding antibonding, or σ* orbital, is defined by the presence of one nodal plane between the two bonded atoms. The extent of this mixing (or hybridization or blending) depends on the relative energies of the MOs of like symmetry.įor homodiatomics (homonuclear diatomic molecules), bonding σ orbitals have no nodal planes at which the wavefunction is zero, either between the bonded atoms or passing through the bonded atoms. As a practical consequence of this mixing of diatomic molecules, the wavefunctions s+s and pz+pz molecular orbitals become blended. Quantum theory also indicates that molecular orbitals (MO) of identical symmetry actually mix or hybridize. By this definition, common forms of sigma bonds are s+s, pz+pz, s+pz and dz2+dz2 (where z is defined as the axis of the bond or the internuclear axis). In this formal approach, a σ-bond is symmetrical with respect to rotation about the bond axis. Sigma bonding is most simply defined for diatomic molecules using the language and tools of symmetry groups. They are formed by head-on overlapping between atomic orbitals. In chemistry, sigma bonds (σ bonds) are the strongest type of covalent chemical bond. Wikipedia Rate this definition: 0.0 / 0 votes
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