# Question 5f606

Apr 19, 2016

Here's what I got.

#### Explanation:

In order for a hydrogen bond to form, you need to have two things

• a hydrogen atom bonded to one of the three most electronegative atoms, $\text{N}$, $\text{O}$, or $\text{F}$
• an electronegative atom that has one or more lone pairs of electrons

A hydrogen atom bonded to a very electronegative atom will act as a hydrogen bond donor. The electronegative atom that has lone pairs of electrons to spare will act as a hydrogen bond acceptor.

When nitrogen, oxygen, or fluorine bond to hydrogen atoms, the significant difference in electronegativity between these atoms and hydrogen causes partial charges to form.

More specifically, the more electronegative atoms will develop a partial negative charge and the hydrogen atom will develop a partial positive charge.

The partial positive hydrogen atom will then form a hydrogen bond with one lone pair present on another electronegative atom. This happens because the partial positive charge present on the hydrogen atom is attracted to the concentrated negative charge of the lone pair of electrons.

You're dealing with a molecule of urea, "CO"("NH"_2)_2#, which contains two $- {\text{NH}}_{2}$ groups and one carbonyl group, $\text{C=O}$.

In order to find the atoms that can form hydrogen bonds with the partial positive hydrogen atoms of a water molecule, you must look for electronegative atoms that have lone pairs of electrons present.

As you can see, the oxygen atom present on the carbonyl group has two lone pairs of electrons, so it can act as a hydrogen bond acceptor for two partial positive hydrogen atoms, one for each lone pair.

Likewise, the two nitrogen atoms can act as hydrogen bond acceptos because they each have one lone pair of electrons present.

In order to find the atoms that can form hydrogen bonds with the partial negative oxygen atom of a water molecule, you must look for hydrogen atoms bonded to one of the three aforementioned electronegative elements.

As you can see, each $- {\text{NH}}_{2}$ group has two hydrogen atoms bonded to nitrogen, which means that it has two partial positive hydrogen atoms that can act as hydrogen bond donor to the partial negative oxygen atom in a water molecule.

Therefore, an urea molecule has three atoms that can act as hydrogen bond acceptors, and four atoms that can act as hydrogen bond donors.