Explanation:
Pi-bonds are covalent bonds that are formed by the overlapping of p orbitals of two atoms. These bonds do not alter the shape of the molecule that is formed by the bonding atoms. The shape of the molecule is determined by the arrangement of the atoms and the lone pairs of electrons on the central atom.

Bond Length:
The bond length is the distance between the nuclei of two bonded atoms. The formation of pi-bonds shortens the bond length because the overlap of the p orbitals brings the nuclei of the bonding atoms closer together.

Bond Energy:
The bond energy is the amount of energy required to break a bond. The formation of pi-bonds increases the bond energy because the overlapping of the p orbitals results in the formation of a stronger bond.

Bond Angle:
The bond angle is the angle between the nuclei of two adjacent atoms in a molecule. Pi-bonds do not alter the bond angle because they are formed perpendicular to the plane of the atoms that are bonded, and so they do not affect the arrangement of the atoms in the molecule.

Bond Frequency:
The bond frequency is the frequency at which a bond vibrates. Pi-bonds do not alter the bond frequency because they do not affect the motion of the atoms in the molecule.

Conclusion:
Pi-bonds are important covalent bonds that are formed by the overlapping of p orbitals of two atoms. These bonds do not alter the shape of the molecule but they do shorten the bond length and increase the bond energy. The bond angle and bond frequency are not affected by the formation of pi-bonds.