Back Pi-binding AF رابطة باي Arabic পাই বন্ধন Bengali/Bangla Pi-veza BS Enllaç pi Catalan Vazba pí Czech Pi-binding Danish Π-Bindung German Δεσμός π Greek Pi bond English
In chemistry, a pi bond (π bond) is a covalent chemical bond where the orbital path of one electron crosses (overlaps) with the path of another. The electrons have a lobe shaped figure of eight path (see picture). There are two areas of overlap as the paths overlap on both lobes. Only one of the orbital's nodal planes passes through both of the involved nuclei.[1]
The Greek letter π in their name refers to p orbitals. The orbital symmetry of the pi bond looks the same as the p orbital when seen down the bond axis. P orbitals usually have this sort of bonding. D orbitals are also assumed to use pi bonding but this is not necessarily what happens in reality. The idea of bonding d orbitals fits in with the theory of hypervalence.
Pi bonds are usually weaker than sigma bonds. Quantum mechanics says this is because the orbital paths are parallel so there is much less overlap between the p-orbitals.
Pi bonds happen when two atomic orbitals are in contact through two areas of overlap. Pi-bonds are more spread out bonds than the sigma bonds. Electrons in pi bonds are sometimes called pi electrons. Molecular fragments joined by a pi bond cannot rotate about that bond without breaking the pi bond. The rotation destroys the parallel paths of the two p orbitals.[2]