# Describe a hydrogen-bond. What conditions must exist for a hydrogen-bond to form?

Apr 2, 2017

$\text{An hydrogen bond is an intermolecular bond................}$

#### Explanation:

That occurs when hydrogen is bound to a strongly electronegative element such as oxygen, nitrogen, or fluorine.

Now electronegative elements bound to hydrogen strongly polarize electron density towards themselves. And thus for $H - F$, we can describe the resulting dipole as ""^(+delta)H-F^(delta-), for $\text{ammonia}$, ""^(-delta)NH_3^(delta+), for $\text{water}$, ""^(-delta)OH_2^(delta+). When the dipoles line up in the condensed phase, this acts as AN EXTRA, POTENT, INTERMOLECULAR force that tends to elevate melting points, and boiling points, with the result that the boiling points of these hydrides are anomalously high.

What are the respective boiling points of each substance?

See here for another scenario.