Question

Define sigma and pi bonds.

Answer 1

Sigma$\left(\mathrm{\sigma }\right)$ bonds:

• A sigma bond is defined as a covalent bond formed by axial overlapping of axial orbitals.
• This strong greater than pi bonds.
• As an example, methane molecule contains $4$ $\mathrm{C}-\mathrm{H}$ bonds, covalent bonds by the overlapping of bonding orbitals along internuclear axis end to end orbitals known as head overlapping.
• These are the overlapping orbitals: s-s, s-p, and p-p overlapping.
• s-s overlapping: Two half-filled s orbital which interact along the internuclear axis.
• s-p overlapping: Take between half-filled s orbitals of one atom and half-filled p-orbitals.
• p-p Overlapping: Overlapping between half-filled p-orbitals.
• These bonds exist independently and free rotation is seen in them.
• It is involved in the control of geometry.
• One sigma bond is involved in pi bond and triple bonds.
• These bonds are reactive and the shape of a molecule is determined by these bonds.

Pi $\left(\mathrm{\pi }\right)$bonds:

• A pi bond is defined as an atomic orbital intersecting positive directional to the internuclear axis.
• The atomic orbitals converge axis parallel to each other and perpendicular to the central axis.
• These are formed through lateral overlap half-filled atomic orbitals.
• Two pure or unhybridized orbitals are alternating orbitals.
• It also exists along with sigma bonds.
• No rotation exists in these bonds.
• It is less strong than sigma bonds.
• It is not involved in the control of geometry.
• One pi bond is observed in double bonds and in a triple bond, there are two pi bonds.
• They are less reactive than the sigma bond.