Question

A hydrogen ion can bond to an ammonia molecule, \(\mathrm{NH}_{3}\), forming \(\mathrm{NH}_{4}^{+}\). Draw the electron dot formula for \(\mathrm{NH}_{4}^{+}\) and label a coordinate covalent bond.

Short answer

The coordinate covalent bond in \(\mathrm{NH}_{4}^{+}\) is formed when nitrogen donates its lone pair to the hydrogen ion.

Step-by-step solution

Understand the Target Molecules

The problem involves two species: - Ammonia, \(\mathrm{NH}_{3}\), which has a lone pair of electrons on the nitrogen atom.- Hydrogen ion, \(\mathrm{H}^+\), which has no electrons.

Draw Lewis Structure for NH3

For ammonia, \(\mathrm{NH}_3\), nitrogen has 5 valence electrons, and each hydrogen has 1 valence electron. When these are combined, nitrogen forms three single covalent bonds with three hydrogen atoms, and there is one lone pair of electrons on the nitrogen atom.

Form the Ammonium Ion

The \(\mathrm{H}^+\) ion can accept a pair of electrons to form a bond. Nitrogen's lone pair forms a coordinate covalent bond with \(\mathrm{H}^+\), creating \(\mathrm{NH}_{4}^{+}\).

Draw the Lewis Structure for NH4^+

In the \(\mathrm{NH}_{4}^{+}\) ion, nitrogen is surrounded by four hydrogen atoms with single bonds. The positive charge indicates one less electron. Typically, the nitrogen atom in \(\mathrm{NH}_{4}^{+}\) shares its lone pair with \(\mathrm{H}^+\), thus the lone pair is now represented as a bonding pair.

Label the Coordinate Covalent Bond

In the Lewis structure of \(\mathrm{NH}_{4}^{+}\), the bond formed by the nitrogen atom donating the entire pair of electrons to the \(\mathrm{H}^+\) is the coordinate covalent bond. This bond can be highlighted with an arrow pointing from nitrogen to the \(\mathrm{H}^+\).

Key concepts

Electron Dot Formula

The electron dot formula, also known as a Lewis structure, is a way to represent the valence electrons of an atom or a molecule. In these diagrams, each dot represents one valence electron. This type of formula helps visualize how atoms are bonded in a compound, showing single, double, or even triple bonds between atoms.
The Lewis structure is essential for understanding molecular geometry and predicting the behavior of molecules. When drawing a Lewis structure, you must know the total number of valence electrons available.
The goal is to arrange these electrons so that each atom achieves a full outer shell, typically guided by the octet rule, meaning eight electrons for elements in the main groups of the periodic table. However, some may have fewer or more, such as hydrogen, which requires only two electrons.

• To draw a Lewis structure: Count all valence electrons in the molecule.
• Place a pair of electrons between each pair of bonded atoms to form a bond.
• Distribute remaining electrons to fulfill the octet rule.
• If necessary, use double or triple bonds to fulfill octet rules.

Coordinate Covalent Bond

A coordinate covalent bond, sometimes called a dative bond, is a special type of covalent bonding where both electrons in the shared pair come from the same atom. These bonds occur when one atom donates a lone pair of electrons to an electron-deficient atom, like in the formation of the ammonium ion (\(\mathrm{NH}_{4}^{+}\)).
In the case of \(\mathrm{NH}_{3}\) and \(\mathrm{H}^{+}\), the nitrogen atom in ammonia uses its lone pair to bond with a proton. This results in the proton becoming bound to the molecule, changing \(\mathrm{NH}_{3}\) to \(\mathrm{NH}_{4}^{+}\). In diagrams, you can denote this bond by using an arrow pointing from the donor atom (nitrogen) to the accepter (hydrogen ion).
This type of bonding is critical in many reactions and complexes, helping to form stable compounds and ions in various chemical processes.

• Features of coordinate covalent bonds:
• Both electrons come from one atom.
• Usually indicated by an arrow in diagrams.
• Creates bonds between electron-rich atoms and electron-poor atoms.

Ammonium Ion

The ammonium ion (\(\mathrm{NH}_{4}^{+}\)) is a positively charged polyatomic ion. It's formed when a hydrogen ion (\(\mathrm{H}^{+}\)) interacts with ammonia (\(\mathrm{NH}_{3}\)). Ammonia has a lone pair of electrons on the nitrogen atom, which makes it possible to donate these electrons to the \(\mathrm{H}^+\), forming the ammonium ion.
When forming \(\mathrm{NH}_{4}^{+}\), the structure changes. Nitrogen, which typically has three hydrogen bonds in \(\mathrm{NH}_3\), acquires a fourth hydrogen through a coordinate covalent bond. This gives \(\mathrm{NH}_{4}^{+}\) a symmetrical, tetrahedral shape with all four N-H bonds equivalent once formed.
The positive charge of the ammonium ion comes from the single electron deficit, due to the nitrogen atom not regaining the electron it used to form the bond with the hydrogen ion.

• Key aspects of the ammonium ion:
• Positively charged due to the additional hydrogen ion.
• Forms when nitrogen donates a lone pair.
• Exhibits a tetrahedral shape.