# Why are single bonds weaker than double?

##### 1 Answer

Simply from how they're constructed. Since a *pure* double bond consists of **1** **1** **one** **bond's worth stronger** than a single bond.

All pure **single bonds** consist of **one** *head-on* orbital overlap.

Below is an example a constructive

#2p_z-2p_z# head-on overlap that forms a#sigma_(2p_z)# molecular orbital, where electron density lies in the white bulged region---betweenthe atoms.

A nice example is

the#\mathbf(sigma)# bond in#\mathbf("Cl"-"Cl")# .

All pure **double bonds** consist of an **additional** *sidelong* orbital overlap.

Below is an example of the

#2p_x-2p_x# constructive/bonding overlap, where electron density lies in the white bulged region (above the atoms).

An explicit

#pi# bond example isthe#\mathbf(pi)# bond in#\mathbf("O"="O")# , a product of either a#2p_x-2p_x# sidelong overlap, or a#2p_y-2p_y# sidelong overlap (but not both), that forms a#pi_(2p_(x"/"y))# orbital, depending on which pair overlaps.This

#pi# bond is madein addition tothe#sigma# bond that wasalreadymade upon forming the first#"O"-"O"# bond.

Therefore, since a *pure* double bond consists of **1** **1** **one** **bond's worth stronger** than a single bond.