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NH3 Lewis Structure & Molecular Geometry

Ammonia (NH3) is a colorless, pungent gas and is made up of nitrogen and hydrogen. In the NH3 Lewis structure, three hydrogen atoms are bound to a nitrogen atom. NH3 molecular geometry is trigonal-pyramidal.

Name of molecule Ammonia (NH3)
Bond Angles107.3 degrees
Molecular Geometry of NH3 Trigonal-Pyramidal
Hybridization of NH3 SP3 hybridization
Electronic configuration 1S22S22P3.
NH3 oxidation numberzero

NH3 molecular geometry

In ammonia molecular geometry, three hydrogen atoms are bonded to a nitrogen atom in the middle.
Nitrogen has 5 electrons in the valence shell, so it needs to combine with 3 hydrogen atoms to fulfill the octet rule.

NH3 has trigonal pyramidal geometry because of the presence of a lone electron pair with the central nitrogen atom. As a result, bonding pairs of electrons push away nonbonding pairs of electrons to form a pyramidal shape. The unbonded electrons are called lone pairs of electrons.

The arrangement of atoms in ammonia

The ammonia molecule is an inorganic compound with a trigonal pyramidal shape.
It contains three hydrogen atoms and an unshared pair of electrons attached to the nitrogen atom.
Strong intermolecular hydrogen bonding makes it highly associated.
It is a polar molecule. The compound ammonia is formed when three hydrogen atoms interact with one nitrogen atom.

Three hydrogen atoms share their electrons with the five outer electrons of nitrogen, essentially giving all four atoms full outer shells. Each hydrogen atom is one electron short of a noble gas structure (full shell), and nitrogen is three electrons short of a full outer shell (of eight).
Three hydrogen atoms and one nitrogen atom combine to form NH3 so that the hydrogen atoms are electronically like helium and the nitrogen atom becomes like neon.
The NH3 molecule is held together by the strong N–H nitrogen–hydrogen single covalent bonds by sharing electrons. The H–N–H bond angle is 107o.

Step by Step Construction of Lewis Structure

The following are the steps to construct the ammonia Lewis Structure.

Step-1: Count the Valence Electrons of Atoms

Ammonia contains two elements; hydrogen and nitrogen. Hydrogen is a Group IA element and has only one electron in its valence shell. Nitrogen is a group VA element in the periodic table and contains five electrons in its last shell. The table below shows the electronic configuration and valence electrons in hydrogen and nitrogen.

AtomElectronic ConfigurationValence Electrons (VEs)
7N1s22s22p35
1H1s11

VEs = VEs in three hydrogen atoms + VE in one nitrogen atom
Valence electrons = 3(1)+5 =8

Step-2: Determine the Central Atom

As per the rule, N is placed in the middle because it has the maximum number of valence electrons, which is five. Hydrogen has only one valence electron. 

Step-3: Place Electron Pairs Between the Atoms

We need to distribute the 8 valence electrons.
In the figure, one electron pair between two atoms is equivalent to one line. Out of eight electrons, six will be used in pairs between atoms. Now we have 2 valence electrons to distribute. In the ammonia Lewis structure, the hydrogen atoms are the outside atoms, and each one of them cannot keep more than two electrons in its last shell. Therefore, we will draw the remaining electron pair on the central nitrogen atom.

Electronic Configuration of Nitrogen in Ammonia

What is a Lone Pair of the Electron?

A lone pair of electrons refers to a pair of electrons that exist without bonding or sharing with other atoms.
A lone pair attracts one nucleus.
Therefore, it adopts a position effectively closer to that one nucleus than the bonding pairs of electrons.
In addition, the lone pair demands a greater angular range.
For instance, in ammonia, the lone pair makes room for itself by pushing the three hydrogen atoms together a little, and the H-N-H bond angles are slightly less (106.6°) than the ideal tetrahedral angle of 109.5°.

What is meant by Lewis structure?

The Lewis structure, also referred to as the electron-dot structure, is a structural formula in which electrons are represented by dots; two dots between two atoms represent a covalent bond. To draw the Lewis structure, we place a dot around the atom for each valence electron available.

Importance of Lewis Structure

Lewis structures are very important for predicting the geometry, polarity, and reactivity of (in)organic compounds. 

Rules for drawing Lewis dot structures

Octet rule

The octet rule states that in forming compounds, atoms tend to gain a stable electron configuration, the electron configuration of the nearest noble gas (8 valence electrons except for He with 2). When atoms have fewer than eight electrons, they tend to react and form more stable compounds.

Limitations of Octet Rule

NH3 Lewis Structure- Key Points

What is Ammonia?

Ammonia also referred to as hydrogen nitride, is a compound of nitrogen and hydrogen.
It is produced artificially by reacting natural gas, namely methane, with steam to form hydrogen in the primary reformer. In the secondary reformer, the air is added to the gas stream. In the converter, the remaining hydrogen and the nitrogen from the air combine in a ratio of 3:1 to produce ammonia. The uncombined gases are recycled back to the converter.

Molecular Geometry of NH3

NH3 molecular geometry is trigonal-pyramidal. The reason for this is that the nitrogen atom has a single non-bonding lone pair of electrons that serve as a repulsive force on the bonding orbitals.
The three hydrogen atoms are bonded to a nitrogen atom in the middle.
Since nitrogen has 5 electrons in its valence shell, it must interact with 3 hydrogen atoms to satisfy the octet rule and produce ammonia, a stable molecule.

Molar Mass of Ammonia

Molar mass of Nitrogen = 14.0067 g/mol.
The hydrogen molar mass is 1.00794 g/mol.
Molar mass of Ammonia (NH3)= 14.0067 g/mol + (3× 1.00794) g/mol = 17.03052 g/mol
= 17.03052 g/mol

Is Ammonia is a strong base?

Ammonia is a weak base. It itself doesn’t contain hydroxide ions, but it reacts with water to produce ammonium ions and hydroxide ions. A weak base is a base that does not completely dissociate into its constituent ions when dissolved in solutions.

Uses of Ammonia

  • Ammonia is used in the manufacture of explosives.
  • dye-making.
  • preparing medicines.
  • used in the production of fertilizers.
  • Ammonia is also used in household cleaning products.

Haber Process

Most of the commercial ammonia is obtained by Haber’s process.
In this process, 1 volume of nitrogen and 3 volumes of hydrogen of purified gases are mixed.
The mixed reactants are then compressed to 200–500 atm pressure by special pumps, injected into the heated reaction vessel, and then passed over the catalyst consisting of a mixture of Fe with a little Molybdenum (Mo) maintained at 400–500 °C.
The emerging reaction mixture (containing about 10% ammonia) is removed perpendicularly by liquefaction. The unreacted nitrogen and hydrogen are recycled. Excess nitrogen is used to favor the reaction to the right.

Haber Process Equation


N2 (gas) +3H2 (gas) → 2NH3(gas).

The chemical reaction between N2 and H2 is exothermic, reversible, and spontaneous. According to the Lechatlier principle, high pressure and low temperature are favorable conditions for the high yield of ammonia.

NH3 Polar Nature

The NH3 molecule is polar. The electronegativity difference between N (3.04) and H ((2.2) makes the N–H bond polar. The difference in their electronegativities causes three dipole moments from the three N-H bonds in one direction.
The three dipoles in one direction form a net dipole moment that makes it a polar molecule.
In addition, the lone pair on the nitrogen atom exerts an outward force on the bond due to which the shape of NH3 becomes unsymmetrical.

Summary

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Frequently Asked Questions (FAQs)

Below are some of the frequently asked questions

1. What is the oxidation number of NH3?

Ammonia is made up of one nitrogen atom and three hydrogen atoms (NH3). The NH3 oxidation number is zero because the sum of the individual oxidation values of the atoms nitrogen (oxidation number =-3) and hydrogen (oxidation number =1) is zero.

3. What is CLF3 molecular geometry?

CLF3 has a T-shaped molecular geometry and trigonal bipyramidal electron geometry. According to the ClF3 Lewis structure, this molecule has two lone pairs and three bound pairs. ClF3 is a polar compound.

Exposure to 300 ppm is dangerous to life and health (IDLH) and can be fatal within a few breaths. Ammonia is corrosive to the skin, eyes, and lungs.

NH3 (ammonia) is a toxic gas.
Ammonium is a nontoxic salt. It is the ionized form of ammonia.
Its ions are produced during ammonification.

Ammonia can irritate the respiratory tract and can cause coughing and shortness of breath. Its inhalation can also cause nose and throat irritation.

Ammonia consists of one negatively charged nitrogen ion and three positively charged hydrogen ions. The pH of standard ammonia is about 11.

Bottom Line

This article explains the steps to draw the Ammonia Lewis structure, the molecular geometry and arrangement of atoms in NH3, the definition of Lewis structure, and the definition of lone pair of electrons. Please feel free to comment if you have any questions.

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Author
Ms. Sana Javed
Sana has been working at Whatsinsight since 2020 as a content writer.
She has an MPhil degree in pharmaceutics.

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