Difference Between Ammonia and Ammonium

Main Difference – Ammonia vs  Ammonium

Ammonia and ammonium are nitrogen-containing compounds. Both are polyatomic compounds that are composed of more than two atoms per molecule or ion. Ammonium is derived from ammonia. Ammonia can be found as a gas while Ammonium can be found in all three phases of matter. Though they have nearly similar chemical compositions, there are many differences between ammonia and ammonium. The main difference between ammonia and ammonium is that ammonia is a neutral compound whereas ammonium is a cation.

Key Areas Covered

1. What is Ammonia
     – Definition, Chemical Structure, Properties
2. What is Ammonium
    – Definition, Chemical Structure, Properties
3. What are the Similarities Between Ammonia and Ammonium
    – Outline of Common Features
4. What is the Difference Between Ammonia and Ammonium
     – Comparison of Key Differences

Key Terms: Ammonia, Ammonium, Ammonium Salt, Azane, Azanium, Cation, Lone Pair, Polyatomic

What is Ammonia

Ammonia is an inorganic compound having the chemical formula NH3. It is a gaseous compound. The molar mass of ammonia is 17.031 g/mol. This compound is alkaline and has a characteristic pungent odor. The IUPAC name of ammonia is azane.

The geometry of ammonia is trigonal pyramidal. Here, the trigonal pyramid is composed of three N-H bonds and a lone electron pair on the nitrogen atom. Although the bond angle of a molecule with typical trigonal pyramidal structure is 109o, due to the presence of a lone pair, the bond angle in ammonia molecule has been reduced to 107o.

Figure 1: Chemical Structure of Ammonia

The melting point of ammonia is -77.73oC and the boiling point is about -33.34oC. When considering the density of ammonia, it is lighter than air. Since there are N-H bonds in this compound, ammonia is easily liquefied into ammonia liquid. This is because N-H bonds can form strong hydrogen bonds with each other. When liquid ammonia is frozen to its melting point, it starts to form white crystals.

Ammonia is miscible with water due to the ability to form hydrogen bonds with water molecules. Boiling aqueous ammonia can expel ammonia from water since ammonia has a very low boiling point when compared to the boiling point of water. Ammonia may undergo combustion in the presence of oxygen. The combustion of ammonia can be observed as a pale-yellow colored flame.  

What is Ammonium

Ammonium is a cation having the chemical formula NH4+. Ammonium ion is an inorganic ion composed of one nitrogen atom and four hydrogen atoms. It has four N-H bonds. Ammonium ion is a polyatomic on. The molar mass of this cation is 18.039 g/mol. The IUPAC name of ammonium ion is azanium.

Ammonium ion has a trigonal pyramidal structure. Here, the four N-H bonds are arranged in trigonal pyramidal structure. Since all the bonds are similar in this molecule, the bond angle is 109o. The molecule is formed when the lone pair on the nitrogen atom of an ammonia molecule is donated to a proton. The proton causes the molecule to have a positive charge. The oxidation number of nitrogen of ammonium ion is -3.

Figure 2: Chemical Structure of Ammonium Ion

Ammonium ion is slightly acidic. It can react with bases and form ammonia gas. When ammonia is dissolved in water, it can form ammonium ions. It is an equilibrium reaction and is highly dependent on the pH of the solution. The reaction is as follows.

H2O    +    NH3     ⇌    OH−    +   NH+4

Ammonium ion can be found commonly in ammonium salts. An ammonium salt is a chemical compound composed of ammonium cation and an inorganic anion. Some examples of ammonium salts include ammonium chloride, ammonium sulfate, and ammonium carbonate. These salt compounds are highly water soluble.

Similarities Between Ammonia and Ammonium

• Both compounds are composed of nitrogen and hydrogen atoms
• Both are polyatomic compounds
• The nitrogen atom has +3 oxidation number in both compounds
• Both have trigonal pyramidal geometry

Difference Between Ammonia and Ammonium

Definition

Ammonia:  Ammonia is an inorganic compound having the chemical formula NH3.

Ammonium:  Ammonium is a cation having the chemical formula NH4+.

Lone Electron Pairs

Ammonia:  Ammonia has a lone electron pair.

Ammonium: Ammonium ion has no lone electron pairs.

IUPAC

Ammonia:  The IUPAC name of ammonia is azane.

Ammonium: The IUPAC name of ammonium ion is azanium.

Nature

Ammonia:  Ammonia is an alkaline compound.

Ammonium:  Ammonium ion is slightly acidic.

Bond Angle

Ammonia:  Bond angle in ammonia is 107°.

Ammonium: Bond angle in ammonium ion is 109°.

Molar Mass

Ammonia:  Molar mass of ammonia is 17.031 g/mol.

Ammonium: Molar mass of ammonium ion is 18.039 g/mol.

Electrical Charge

Ammonia:  Ammonia is a neutral compound.

Ammonium: Ammonium ion has +1 electrical charge.

Conclusion

Ammonia and ammonium are two related compounds composed of nitrogen and hydrogen atoms. Ammonium ion is derived from ammonia. The main difference between ammonia and ammonium is that ammonia is a neutral compound whereas ammonium is a cation.

References:

1. “Ammonium.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, Available here.
2. “Ammonia.” Wikipedia, Wikimedia Foundation, 2 Dec. 2017, Available here.
3. “Ammonia.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, Available here.

Image Courtesy:

1. “Ammonium-2D” By Lukáš Mižoch – Own work (Public Domain) via Commons Wikimedia
2. “Ammonia lone electron pair” By Booyabazooka (vectorization) – Own work (Public Domain) via Commons Wikimedia

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