Ammonia Lewis Structure

Ammonia Lewis Structure: NH₃ Lewis Structure, Trigonal Pyramidal Geometry, sp³ Hybridization & Polarity

Ammonia Key Facts

The ammonia Lewis structure is a central nitrogen bonded to three hydrogens with one lone pair on nitrogen (H₃N:); the molecule is trigonal pyramidal, nitrogen is sp³-hybridized, the H–N–H angle is about 107°, and because the pyramidal shape prevents dipole cancellation, NH₃ is polar.

Figure 1: Lewis Structure of Ammonia (NH₃)

Chemical Formula	NH₃
CAS Number	7664-41-7
Total Valence Electrons	8
Lewis Structure	Central N with 3 N–H bonds + 1 lone pair
Electron-Domain Geometry	Tetrahedral
Molecular Geometry	Trigonal pyramidal
Hybridization Model	sp³ (nitrogen)
H–N–H Bond Angle	≈ 107°
Polarity	Polar molecule

PubChem and NIST identify ammonia as NH ₃ with CAS 7664-41-7; PubChem lists a molecular weight of approximately 17.031 g/mol. View CAS 7664-41-7 dictionary details on Guidechem →

Applications of Ammonia (CAS 7664-41-7)

Ammonia is one of the most-produced chemicals in the world, almost entirely via the Haber–Bosch process from nitrogen and hydrogen. The majority is used in fertilizers (urea, ammonium nitrate, ammonium phosphate), underpinning modern agriculture and food production.

Beyond fertilizer, NH₃ is oxidized to nitric acid (Ostwald process), a precursor to explosives, nitrates and adipic acid; it is used as a refrigerant (especially in industrial and large-scale cooling), as a cleaning agent (ammonium hydroxide), and as a feedstock for nylon intermediates (caprolactam, adipic acid). Its alkaline, nucleophilic character makes it a versatile reagent across the chemical industry.

Fertilizers Urea, ammonium nitrate and ammonium phosphate — the backbone of synthetic nitrogen fertilizer.

Nitric Acid & Explosives Ostwald-process oxidation to nitric acid for nitrates, adipic acid and energetic materials.

Refrigeration & Cleaning Industrial refrigerant (R717) and ammonium-hydroxide cleaning/process chemistry.

Procurement Note Ammonia is supplied as anhydrous liquid (under pressure) or as aqueous ammonium hydroxide, in grades from agricultural to refrigeration/food/electronic. Because NH₃ is pungent, corrosive and a health hazard at high concentration, procurement must address storage, vapor management and material compatibility. Use CAS 7664-41-7 as the primary identifier and specify grade and concentration.

Step 1 - Valence Electrons & Central Atom

Count valence electrons for NH₃: nitrogen is in Group 15 and contributes 5 valence electrons. Each of the three hydrogens contributes 1 valence electron.

Valence-electron count

Total valence electrons = 5 from N + 3 × 1 from H = 8 electrons.

Step 2 - Lewis Structure & Electron Distribution

Place nitrogen at the center and attach the three hydrogens: H–N–H (with a third H). Three N–H single bonds consume 6 of the 8 electrons, leaving 2 electrons as one lone pair on nitrogen.

Nitrogen now shares three bonding pairs (6 electrons) plus one lone pair (2 electrons) = 8 electrons (octet); each hydrogen has its duet. The structure H₃N: has zero formal charge on every atom.

H
H – N – H
H

Central nitrogen bonded to three hydrogens (pyramidal)

3 N–H bonds + 1 lone pair on N = 4 electron domains

Octet Rule in Ammonia Nitrogen in NH₃ forms three N–H bonds (6 shared electrons) and retains one lone pair (2 electrons), giving a complete octet. Hydrogen atoms each achieve the duet. No expanded octet is needed; nitrogen is a second-row element and the standard Lewis structure satisfies the octet rule directly with zero formal charge.

Step 3 - VSEPR Theory & Geometry

The Lewis structure gives four electron domains around nitrogen: three bonding domains and one lone pair. Four domains adopt an approximately tetrahedral electron-domain geometry to minimize repulsion.

Because one domain is a lone pair (not a vertex of the molecule), the molecular geometry is trigonal pyramidal, not tetrahedral. The lone pair repels the N–H bonds more strongly, compressing the H–N–H angle from 109.5° to about 107°.

Repulsion hierarchy

The VSEPR ordering is lone pair–bonding pair repulsion > bonding pair–bonding pair repulsion. The nitrogen lone pair occupies more space and pushes the three N–H bonds downward, creating the pyramid and narrowing the bond angle slightly below the tetrahedral ideal.

Hybridization & Formal Charge

In the localized-bond model, nitrogen in NH₃ is described as sp³-hybridized: four electron domains correspond to four tetrahedral hybrids. Three form σ bonds to hydrogen and one holds the lone pair.

The lone pair occupies slightly more space than a bonding hybrid, which is why the geometry is pyramidal and the bond angle is slightly compressed relative to a perfect tetrahedron.

Formal-charge check

Formal charge = valence − nonbonding − ½ × bonding. Nitrogen in NH₃: 5 − 2 − ½×6 = 0. Each hydrogen: 1 − 0 − ½×2 = 0. Every atom has zero formal charge, confirming the H₃N: structure is dominant.

Modeling Note sp³ hybridization is a useful model for ammonia's four electron domains. Modern MO treatments describe the lone pair as largely localized on nitrogen with some s-character; the pyramidal geometry and ~107° angle are correctly predicted by the VSEPR/hybridization picture.

Is Ammonia Polar or Nonpolar?

Ammonia is polar. Each N–H bond is polar because nitrogen is more electronegative than hydrogen, and the molecule is trigonal pyramidal rather than planar.

The three N–H bond dipoles do not cancel; their vector sum points roughly along the C₃ symmetry axis toward the nitrogen lone pair, giving NH₃ a substantial dipole moment (about 1.47 D). This polarity underlies ammonia's solubility in water and its behavior as a base.

Expert Quote — Structural Chemistry Perspective

"Ammonia's polarity and basicity both trace to the same feature: the nitrogen lone pair. It defines the pyramidal geometry (so bond dipoles don't cancel) and it is the site that accepts a proton to form ammonium."

Interpretation consistent with VSEPR and Brønsted–Lowry base behavior of ammonia.

This lone-pair-driven polarity also explains why NH₃ is highly soluble in water, forms hydrogen bonds, and readily accepts a proton to give NH₄⁺ — the chemistry behind its use as a fertilizer nutrient and as a base in process chemistry.

Structural Comparison Table

Species	Formula	Central Atom	Electron Domains	Molecular Geometry	Polarity
Ammonia	NH₃	N	4	Trigonal pyramidal	Polar
Water	H₂O	O	4	Bent	Polar
Methane	CH₄	C	4	Tetrahedral	Nonpolar
Phosphine	PH₃	P	4	Trigonal pyramidal	Weakly polar
Ammonium ion	NH₄⁺	N	4	Tetrahedral	Ionic species

Practice question Add a proton to NH₃ to form NH₄⁺. How do the electron domains, molecular geometry and polarity change? Work from the Lewis structures rather than memorizing.

Looking for industrial bulk or specified-grade supplies of Ammonia (CAS 7664-41-7)? Browse Supplier on Guidechem →

FAQs

What is the Lewis structure of NH₃?

A central N with three N–H bonds and one lone pair (H₃N:). All 8 valence electrons are accounted for with zero formal charge.

Is NH₃ polar or nonpolar?

Ammonia is polar. Its pyramidal shape prevents the three polar N–H bond dipoles from canceling.

What is the bond angle in ammonia?

The H–N–H angle is about 107°. Four electron domains give a tetrahedral arrangement compressed slightly by the lone pair.

What is the hybridization of nitrogen in NH₃?

Nitrogen is sp³-hybridized. Four domains (3 bonds + 1 lone pair) correspond to four tetrahedral hybrids.

What is the CAS number of ammonia?

The CAS number is 7664-41-7. PubChem (CID 222) and NIST identify this with NH₃.

References

PubChem, Ammonia, CID 222. Molecular formula, CAS number and molecular weight (≈17.031 g/mol).
NIST Chemistry WebBook, SRD 69, Ammonia. Formula, CAS Registry Number, thermochemical and spectroscopic data.
IUPAC Gold Book, "lone pair" and "base (Brønsted)." Definitions underpinning the NH₃ structure and basicity.
Smil, V., Enriching the Earth. Haber–Bosch process and the role of ammonia in global fertilizer supply.
Atkins, P. & de Paula, J., Physical Chemistry. VSEPR, molecular symmetry and dipole moments of pyramidal molecules.

Technical scope: Lewis structures, VSEPR and hybridization are model-based descriptions for chemical communication; actual electronic structure is better described by molecular-orbital methods. Commercial ammonia is supplied as anhydrous liquid or aqueous solution in multiple grades; CAS 7664-41-7 identifies the substance, not a specific concentration or purity.

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Ammonia Lewis Structure

Ammonia Lewis Structure