Question

Why are pi bonds formed?

Answer 1

pi bonds are used to form double and triple bonds covalent bonds between atoms

Explanation:

There is only one s orbital in any given energy level. Sharing the S orbital creates only one bond. To make a double bond the p bonds must be used.

The sharing of p orbitals creates pi bonds.

For example `N2` has three bonds. The triple bond requires the sharing of the one S orbital and two P orbitals . The S orbitals overlap directly forming a covalent bond. The two sets of p orbitals overlap side by side creating the pi bonds, which are also covalent bonds

Answer 2

π bonds are formed because the side-by-side overlap of `p` orbitals leads to a lower-energy state than if there were no overlap.

Explanation:

Consider the formation of ethylene, `"H"_2"C=CH"_2`.

The `"C"` atoms are `sp^2` hybridized.

The `"C-C"` σ bond is formed by the overlap of the `"C"` `sp^2` orbitals, and the `"C-H"` σ bonds are formed by the overlap of the `"H"` `1s` orbitals with the `"C"` `sp^2` orbitals.

This leaves an unhybridized p orbital containing one electron on each `"C"` atom.

When you have two `p` orbitals on adjacent `"C"` atoms, they can overlap sideways to form a region of electron density that is not directly between the two nuclear centres but which still contributes to bonding.

We call this a π bond.

It forms because the π electrons are as close as they can get to the two nuclei and are therefore in their lowest energy state.

A π bond can only form only after a σ bond has already formed. It is always part of a double or triple bond.