Why are hydrogen bonds so strong relative to other dipole-dipole bonds?

[TJ Lai 2H]

Why are hydrogen bonds uniquely strong among dipole-dipole forces? For example, why are dipole-dipole bonds involving H so much stronger compared to dipole-dipole bonds involving an element that is even less electronegative, such as Si, or approximately the same electronegativity, such as P? Also, what is unique about N,O,& F and hydrogen bonds? Why would hydrogen bonds not form between an H atom and a Cl atom?

[Gabby Magat 3F]

I think it's because the difference in electronegativity between H and N/O/F bonds is so much larger than those in dipole-dipole bonds. Hydrogen bonds are stronger because the H-N/O/F bonds have the strongest permanent dipoles (this makes sense when you consider other possible dipoles, and a bond between H and N/O/F will always have the greatest electronegativity difference).

[EmilyC_3D]

I would agree with what other people said! F-O-N are some of the most electronegative atoms so would have the strongest dipole moment. I could be wrong but I remember hearing that, in a Hydrogen bond, the electrons are also attracted much closer to the nucleus due to less orbitals in the atom. This might apply to something else though so I'm not sure!

[Nina Tartibi 1F]

Hydrogen bonds are the strongest bond because N,O, and F are the most electronegative elements on the periodic table, and H is one of the least, so there is a large difference in electronegativity, which causes the strongest dipole moment --> strongest IMF

[Khoa Vu 3l]

Hydrogen bonding is so strong among dipole-dipole interactions because it itself is a dipole-dipole interaction with one of the strongest possible electrostatic attractions. Remember that hydrogen bonding cannot occur unless hydrogen is covalently bonded to either oxygen, nitrogen, or fluorine. This is because by covalently bonding to these elements, hydrogen will then bear the largest possible positive partial charge given that oxygen, nitrogen, and fluorine are the most electronegative and, therefore, become some of the most partially negatively charged atoms. With its high partial positive charge in one molecule, hydrogen's strong partial positive charge will be electrostatically attracted to the strongest partially negative charge of oxygen, nitrogen, and fluorine on other molecules, forming the intermolecular force that we know as hydrogen bonding.

[Susanna Givan 2B]

The strength in hydrogen bonding largely depends on the large difference in electronegativity, correct?

[Izamary Marquez 2H]

Are hydrogen bonds ALWAYS present in N,O,F atoms? or is this just likely where they are to be found?

[Manseej Khatri 2B]

Are hydrogen bonds ALWAYS present in N,O,F atoms? or is this just likely where they are to be found?

Hydrogen bonds occur when a hydrogen is covalently bonded to a N, O, or F and is close to an N, O, or F with a lone pair present. If it is not, the it experiences the other intermolecular forces I believe.

[Ayesha Aslam-Mir 3C]

Hydrogen bonding is so strong among dipole-dipole interactions because it itself is a dipole-dipole interaction with one of the strongest possible electrostatic attractions. Remember that hydrogen bonding cannot occur unless hydrogen is covalently bonded to either oxygen, nitrogen, or fluorine. This is because by covalently bonding to these elements, hydrogen will then bear the largest possible positive partial charge given that oxygen, nitrogen, and fluorine are the most electronegative and, therefore, become some of the most partially negatively charged atoms. With its high partial positive charge in one molecule, hydrogen's strong partial positive charge will be electrostatically attracted to the strongest partially negative charge of oxygen, nitrogen, and fluorine on other molecules, forming the intermolecular force that we know as hydrogen bonding.

This is a really good explanation, but to simplify it I like to think of water being a polar molecule (thinking of that dipole moment), and how the electronegativity difference between O and H, and how it gives water unique properties!

[TJ Lai 2H]

Thanks for everyone's responses! I still don't really understand why hydrogen bonds are unique in that they are so much stronger relative to other dipole-dipole bonds (-20 kJ/mol vs. -2 kJ/mol). It doesn't totally make sense to me that hydrogen bonds are 10X stronger than other dipole-dipole bonds only because there is a great electronegativity difference between H atoms and NOF atoms, because there are many elements that are just as electronegative (e.g. P), or even more electronegative (e.g. Si) relative to H. Thanks!

[Wasila Sun 2I]

Thanks for everyone's responses! I still don't really understand why hydrogen bonds are unique in that they are so much stronger relative to other dipole-dipole bonds (-20 kJ/mol vs. -2 kJ/mol). It doesn't totally make sense to me that hydrogen bonds are 10X stronger than other dipole-dipole bonds only because there is a great electronegativity difference between H atoms and NOF atoms, because there are many elements that are just as electronegative (e.g. P), or even more electronegative (e.g. Si) relative to H. Thanks!

Not only is their a greater electronegativity difference between H and N,O,F, but compared to P, S, Cl, etc. the atoms are smaller. A smaller atom means that the electron's attraction or effective nuclear charge is greater to the protons in the nucleus. The electrons are more tightly held in N, O, and F which makes the resulting bond to Hydrogen much, much stronger (because the pull towards the more electronegative atom's nucleus is greater). In the larger atoms that you mentioned, the pull is much weaker not only in terms of electronegativity but the electrons are held less tightly (larger atomic radius) and experience less pull towards the nucleus' protons. So, the resulting bond would not be as strong and the bond would have to be longer given their larger size. Longer bonds are inherently weaker.

[Jaden Kwon 3C]

Compared to other dipole-dipole bonds, the electronegativity difference between hydrogen and O/F/N is very high which makes for stronger bonds which play a huge role in biological and chemical molecules such as DNA.