Draw some molecules of ammonia, \(\mathrm{NH}_{3}\), and use dotted lines to show the hydrogen bonding between them.

Understanding the chemical bonds in ammonia is crucial for explaining its physical and chemical properties. Ammonia (H_{3}) is a compound consisting of one nitrogen atom bonded to three hydrogen atoms. The nitrogen-hydrogen (N-H) bond is a covalent bond, where the two atoms share electrons. However, the shared electrons are not evenly distributed between the nitrogen and hydrogen atoms.

Nitrogen, being more electronegative, attracts the shared electrons more strongly, causing a partial negative charge on the nitrogen and a partial positive charge on the hydrogen. This difference in electronegativity is the key to hydrogen bonding. When a hydrogen atom is attached to a highly electronegative atom, such as nitrogen, and comes near another electronegative atom with a lone pair of electrons (like another nitrogen atom), a hydrogen bond is formed. This bond, represented by dotted lines in molecular diagrams, is weaker than a covalent bond but is significant in determining the molecule's properties.

The hydrogen bonds in ammonia result in higher boiling points compared to other molecules of similar size and contribute to ammonia's distinctive physical characteristics, such as its ability to act as a solvent for many ionic compounds.

Ammonia's molecular structure is fascinating and plays a critical role in its ability to form hydrogen bonds. The molecule adopts a trigonal pyramidal shape, with the nitrogen atom at the apex and three hydrogen atoms at the corners of the pyramid base. This shape arises due to the repulsion between the lone pair of electrons on the nitrogen and the bonding pairs in the N-H bonds.

The presence of a lone pair on the nitrogen atom not only gives the molecule its distinctive shape but also introduces a region of high electron density that can serve as the site for hydrogen bonding with neighboring molecules. The bond angles in ammonia are approximately 107°, slightly less than the ideal 109.5° for a regular tetrahedron, due to the lone pair electron cloud repelling the bonding hydrogen atoms more strongly than the bond pairs repel each other.

Due to its shape, the nitrogen atom is able to participate in hydrogen bonding, and these interactions are essential for the physical properties of liquid ammonia, such as its relatively high boiling point for a molecule of its size.

The concept of lone pair electrons is pivotal in chemistry, particularly in the context of molecules like ammonia. Lone pairs refer to pairs of valence electrons that are not involved in chemical bonding; instead, they reside on an atom and contribute to its overall electron density. In the case of ammonia, the nitrogen atom has one lone pair.

The presence of this pair of non-bonding electrons creates an area on the nitrogen atom that can attract the positively charged hydrogen atoms of nearby ammonia molecules, leading to the formation of hydrogen bonds. The lone pair electrons are also responsible for the shape of the ammonia molecule, as their repulsion against the N-H bonding pairs leads to the trigonal pyramidal geometry.

Lone pair electrons not only influence the structural aspect but also affect reactivity. Molecules with lone pairs can act as Lewis bases, donating electron pairs to form additional chemical bonds. This ability is central to many reactions involving ammonia, such as its reaction with hydrogen ions to form ammonium ions (H_{4}^+). Overall, the concept of lone pair electrons is integral to understanding chemical reactivity and intermolecular forces in substances like ammonia.