[Michael]

hi guys,

I'm quite confused in the interaction that presents in water ?! I'm confused between dipole-dipole interaction and hydrogen bond. so which of them and why its not the other!

thanks in advance

[Yggdrasil]

A hydrogen bond is a type of dipole-dipole interaction, but it is much stronger than a typical dipole-dipole interaction.  Beacuse of the ease with which hydrogens can dissociate with F, O, and N atoms (think: acid/base chemistry), hydrogen bonds have a slight covalent character (as seen by the prefered geometries of hydrogen bonds).  Most other dipole-dipole interactions have no covalent character and are typically much weaker than hydrogen bonds.

[Michael]

Most other dipole-dipole interactions have no covalent character

could you please explain this sentence little bit more ?? especially " have no covalent character "

if it doesn't have covalent character, which character does it have? with examples please

appreciate it

[Yggdrasil]

In a covalent bond, electrons are shared between two atoms.  For example, in H₂, each hydrogen atom donates an electron to form a single bond consisting of two electrons.  These two electrons reside in a molecular orbital (as opposed to an atomic orbital) which lies in between the two hydrogen atoms.

In dipole-dipole interactions, there is no sharing of electrons.  The interaction is an electrostatic interaction (i.e. an attraction between a positive and negative charges).  It is similar to the attraction between Na⁺ and Cl^- in the ionic bonds of table salt, but dipole-dipole interactions are much weaker because molecules with dipoles do not carry full positive or negative charges.  For example, in acetone (which has a dipole), the oxygen carries a slight negative charge while the carbonyl carbon carries a slight positive charge.

In water, some electrons are shared between the lone pair of the oxygen in the hydrogen-bond acceptor and the hydrogen in the hydrogen-bond donor.  So instead of being just a weak electrostatic interaction between the slight positive charge of the hydrogen and the slight negative charge of the oxygen, the bond is said to have characteristics of a covalent bond because of the sharing of electrons.  Since covalent bonds are very strong, this slight covalent character greatly strengthens the interaction between water molecules.

[Michael]

everything is clear now!

Thanks ever so much for your help, I really appreciate it