I have a lot of confusion regarding atomic orbitals and I don't know if what I am having in mind is even correct or not.

The bond dissociation energy of H-H is greater than that of Cl-Cl and as far as I can make out, it is because in H-H, there is an s-s overlap whereas in Cl-Cl, there is a p-p overlap. Because s-s is more compact, therefore more energy is required to break the bond.

Assuming what I wrote above to be correct, this means an s-s bond is stronger than p-p bond. But then, bond strength of p-p is more than that of s-s because of greater extent of overlap.

So there is definitely something/everything wrong in what I am thinking.

In short, how is the bond strength related to other things like stability, energy, bond length (bond length of s-s < s-p < p-p?).

Kindly help because I cannot find any of my queries anywhere else.

  • 4
    $\begingroup$ I'm not sure that there's a good way to compare between H-H and Cl-Cl solely based on the type of orbital. Your rationalisation doesn't sound convincing at all to me. $\endgroup$ Commented Nov 21, 2016 at 17:46

2 Answers 2


There are several factors that affect bond disassociation energies (bond enthalpies) but one quick correlation you can make is bond distance vs bond strength. The interatomic distance of the H2 bond is 74 pm vs 199 pm in Cl2. The H2 bond consists of 1S electrons that are very close to the nucleus, giving a short bond. The valence electrons in Cl2 are 3p (relatively far away). This leads to other properties such as polarizability.

In short your first assumption is incorrect, the trend you are seeing has nothing to do with s or p bonds, but on the bond lengths. Therefore comparing s-s bonds and p-p bonds is meaningless unless you take into account the atomic orbital number and therefore an estimate of bond length.

For your final questions, the stronger the bond, the more stable, the higher energy, and the shorter the bond.

For more info this UF link has good information:http://www.science.uwaterloo.ca/~cchieh/cact/c120/bondel.html

  • $\begingroup$ The stronger the bond, the more stable, the higher energy, and the shorter the bond. So in this way, a 2s-2s bond is shorter than a 2p-2p bond, and also stronger? But then the strength of a p-p bond > s-s bond. Can you kindly explain? $\endgroup$ Commented Nov 22, 2016 at 2:29
  • $\begingroup$ @Cheapstrike a 2s-2s bond is practically impossible because you will run into p-orbitals (which are directional) on both atoms. $\endgroup$
    – Jan
    Commented Nov 23, 2016 at 0:06

There is a vague correlation between bond energy and length, but only in that longer bonds involving larger atoms are weaker. The figure shows some data. The data are for bonds between many different types of atoms and involve single, double and triple bonds. bond-energy-length

data from http://www.wiredchemist.com/chemistry/data/bond_energies_lengths.html and references therein.


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