Ammonia NH3 Ionic or Covalent/ Molecular Bond?


Ammonia occurs in a free as well as a combined state. In Free state: Ammonia is present in small amounts in the air and in traces in natural water. Whereas, in Combined state: In nature, ammonia occurs in combined form in many compounds such as ammonium chloride, ammonium sulfate, etc.

Ammonia and ammonium compounds being highly soluble in water, do not occur as minerals. It has a pungent smell which one encounters near a decaying heap of organic matter or a toilet is due to ammonia. It is produced due to bacterial decomposition of urea (NH2CONH2), present in the urine.

Is Ammonia Ionic or Covalent Bond?

Ammonia NH3 is surely a covalent bond. Three Hydrogen atoms share their outermost electrons with a nitrogen atom in order to complete the outermost octet. This results in achieving minimum energy and maximum stability. During the process, after becoming a covalent bond both atoms attain the nearest noble gas configuration.

Langmuir, in 1919 improved the Lewis concept. He suggests that only those atoms take part in a chemical combination that has short of electrons and wants to acquire the nearest noble gas configuration. They can share their electrons in order to complete their octets. Each atom contributes the same number of electrons to form common pairs which are then shared by both atoms.

molecular structure Ammonia NH3

As you can see from the diagram below, The shared pairs of electrons present between the atoms are called bond pairs because they are responsible for the bonding between the atoms.

On the other hand, the valence electrons which are not involved in bonding'(i.e. sharing) are shown called non-bonding or lone pairs or unshared pair of electrons.

Forms of Ammonia

Ammonia is used commonly in the following forms:

  1. Gaseous ammonia (dry ammonia gas)
  2. Liquid ammonia. When dry ammonia is liquefied by applying high pressure it is called liquid ammonia.
  3. Liquor ammonia fortis is a saturated solution of ammonia in water. It is called .880 ammonia. It has a relative density of 0.880. It is stored in tightly stoppered bottles in a cold place.
  4. Laboratory bench reagent : Dilute solution of liquor ammonia is used as a laboratory reagent.

Ammonia NH3 A Covalent/Molecular Bond

The explanations above, also clear that the

  • Single bond formation is represented by a single line (–).
  • Covalent bond may also be formed by the contribution of two or three electrons.

Let us examine the formation of an ammonia molecule NH3. In this case, the three hydrogen atoms with one nitrogen atom combine to produce ammonia.

NH3 Covalent bond

What we are seeing over here is– Each hydrogen atom (Z=1) is short of one electron to attain a stable configuration of helium. Whereas nitrogen having the atomic number Z= 7 needs three more electrons to have a stable configuration of argon. They can fulfill requirements if they make a covalent bond.

Each of them contributes one electron to form a commonly shared pair. By doing so, all three hydrogen atoms and one nitrogen atom complete their octet and are generally represented by and closing dots around the symbol by a circle or eclipse.

Overall, no doubt, the Lewis dot structure is a powerful method to understand the formation of a molecule to a greater extent. However, this structure has a number of limitations. Further scientists have improved the way of explaining the formation of molecules in their own developed methodology.

Advantages of Ammonia as refrigerant

  1. Ammonia is environmentally compatible. It does not deplete ozone layer and does not contribute the global warming.
  2. It has superior thermodynamic qualities as a result ammonia refrigeration systems use less electricity.
  3. Ammonia has a recognizable odour and so leaks are not likely to escape.

Ammonia has some disadvantages. It is not compatible with copper, so it cannot be used in any system with copper pipes. Ammonia is poisonous in high concentration although it is easily detectable due to its peculiar smell and also being lighter than air goes up in the atmosphere not affecting life too much on earth.

Ammonia solution is used as an important laboratory reagent in the qualitative analysis as it gives characteristic colored metallic hydroxide precipitates.

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