A typical double bond consists of one sigma bond and one pi bond; for example, the C=C double bond in ethylene. A typical triple bond, for example in acetylene, consists of one sigma bond and two pi bonds in two mutually perpendicular planes containing the bond axis.
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Pi bonds are usually weaker than sigma bonds; the C-C double bond has a bond energy less than twice the C-C single bond bond energy; which leads to the conclusion that the p orbital overlap to form molecular orbitals is a weaker bond than when s orbitals overlap to form molecular orbitals.
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Pi bond. In chemistry, pi bonds are covalent chemical bonds where two lobes of one involved atomic orbital overlap two lobes of the other involved atomic orbital.
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Share. By Anne Marie Helmenstine, Ph.D. Definition: A pi bond is a covalent bond formed between two neighboring atom's unbonded p-orbitals. An unbound p-orbital electron in one atom forms an electron pair with a neighboring atom's unbound, parallel p-orbital electron. This electron pair forms the pi bond.
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(σ and π bonds), covalent chemical bonds characterized by a definite but varying spatial symmetry in the distribution of electron density. A covalent bond is formed as a result of the sharing of electrons between interacting atoms. The resultant electron cloud of the σ bond is symmetrical about the line of the bond, that is, the line connecting the nuclei of the interacting atoms (Figure l,a). Single bonds in chemical compounds are usually σ bonds. The electron cloud of the π bond is symmetrical about the plane passing through the inter-nuclear line (Figure l,b), and the electron density in this plane, called the nodal plane, is equal to zero.
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Definition. A molecular orbital in which the electron density is concentrated in the internuclear region. The energy of a bonding molecular orbital is lower than the energy of the separate atomic orbitals from which it forms.
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Pi-bonds are more diffuse bonds than the sigma bonds. Electrons in pi bonds are sometimes referred to as pi electrons. Molecular fragments joined by a pi bond cannot rotate about that bond without breaking the pi bond, because rotation involves destroying the parallel orientation of the constituent p orbitals.
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Polarizability. Definition. The ease with which the electron cloud of an atom or a molecule is distorted by an outside influence, thereby inducing a dipole moment. The ease with which the electron cloud of an atom or a molecule is distorted by an outside influence, thereby inducing a dipole moment.
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Schematic representation of the spatial orientation of orbitals in the formation of (a) σ bonds as a result of s-s, s -ρσ, and Pσ-Pσ interaction and (b) π bonds as a result of ρπ-ρπ, ρπ-dπ, and dπ-dπ interaction. The use of the Greek letters σ and π is related to their correspondence to the Latin letters s and p.
http://encyclopedia2.thefreedictionary.com/Sigma+and+Pi+Bonds
The same plane is also a nodal plane for the molecular orbital of the pi bond. Two p-orbitals forming a π-bond. The Greek letter π in their name refers to p orbitals, since the orbital symmetry of the pi bond is the same as that of the p orbital when seen down the bond axis. P orbitals often engage in this sort of bonding. D orbitals also engage in pi bonding, and form part of the basis for metal-metal multiple bonding.
https://en.wikipedia.org/wiki/Pi_bond
pi bond definition
A pi bond is a covalent chemical bonds where two lobes of one involved atomic orbital overlap two lobes of the other involved atomic orbital.   Pi bonds are covalent chemical bonds where two lobes of one involved atomic orbital overlap two lobes of the other involved atomic orbital.