Is NH4+ polar or non-polar? - Polarity of NH4+

[NH₄]⁺ is the chemical formula for an ammonium ion. It is a positively charged cation with a molar mass of 18.04 g/mol. [NH₄]⁺ is an acid, and ammonia is its conjugate base.

It is used as an important nitrogen source for many plant species, particularly those that grow in hypoxic soils.

To find out whether the ammonium [NH₄] ⁺ ion is polar or non-polar, continue reading the article.

Is [NH₄]⁺ polar or non-polar?

Ammonium [NH₄]⁺ ion is a non-polar molecular ion. It consists of one nitrogen (N) atom and four hydrogens (H) atoms. The nitrogen is kept at the central position, and all hydrogen atoms are at the surrounding positions, making a tetrahedral molecular geometry and shape.

An electronegativity difference of 0.84 units exists between the bonded atoms of nitrogen and hydrogen in the N-H bond in [NH₄]⁺. Thus, each N-H bond is individually polar in [NH₄]⁺ and possesses a specific dipole moment value (symbol µ).

In the [NH₄]⁺ ion, the strongly electronegative nitrogen atom attracts the shared electron pair from each N-H bond to a greater extent as compared to the hydrogen atom. No lone pair of electrons is present on the central nitrogen atom. Hence, no distortion is witnessed in the shape and geometry of NH₄⁺.

The charged electron cloud stays uniformly distributed over the molecule. Due to the symmetrical tetrahedral shape of [NH₄]⁺, the dipole moments of the individually polar N-H bonds get canceled equally.

As a result, the [NH₄]⁺ ion is overall a non-polar molecular ion (net µ = 0).

Name of molecule	Ammonium [NH4]+
Bond type	Polar covalent
Molecular geometry	Tetrahedral
Polar or Non-polar?	Overall Non-polar
Dipole moment	0
Bond angle	∠H-N-H= 109.5°

What makes a molecule polar or non-polar?

A molecule is polar if there is a non-uniform charge distribution present in it. If the charge distribution gets equally balanced in different parts, then that molecule or molecular ion is considered non-polar.

The following three factors mainly influence the polarity of a molecule or molecular ion:

• The electronegativity difference between two or more covalently bonded atoms
• Dipole moment
• Molecular geometry or shape

Now, let us discuss the effect of the above three factors one by one to prove that the ammonium [NH₄]⁺ ion is, overall, a non-polar molecular ion.

Factors affecting the polarity of NH₄⁺

Electronegativity

It is defined as the ability of an elemental atom to attract a shared pair of electrons from a covalent chemical bond.

Electronegativity increases across a period in the Periodic Table while it decreases down the group.

Greater the electronegativity difference between bonded atoms in a molecule or molecular ion, the higher the bond polarity.

Nitrogen (N) is present in the Group VA of the Periodic Table. The electronic configuration of nitrogen is 1s² 2s² 2p³. As per the electronic configuration, an N-atom has a total of 5 valence electrons; it is thus short of 3 valence electrons that are required so that the nitrogen atom can achieve a complete octet electronic configuration.

Conversely, hydrogen (H) is present in Group IA of the Periodic Table. The electronic configuration of hydrogen is 1s¹. According to this electronic configuration, an H-atom has 1 electron in its valence shell and lacks one more electron to achieve a complete duplet.

The Lewis dot structure of NH4+ contains four N-H bonds making a tetrahedral molecular shape. All four valence electrons of nitrogen used in chemical bonding denote there is no lone pair on the central N-atom in NH4+.

In this way, all bonded atoms attain a completely stable electronic configuration via chemical bonding in [NH₄]⁺.

Due to the absence of any lone pair of electrons on the central N-atom in [NH₄] ⁺, there is no distortion in its symmetrical tetrahedral shape or geometry.

Atom	Electronic configuration	Valence electrons
Nitrogen (7N)	1s2 2s2 2p3	5
Hydrogen (1H)	1s1	1

The electronegativity difference in between an N-atom (E. N= 3.04) and an H-atom (E. N= 2.20) in each of the four N-H bonds present in NH₄⁺ ion is 0.84 units.

Hence, the central nitrogen atom with higher electronegativity gains a partial negative (N^δ-) charge while the hydrogen atoms in its surroundings obtain partial positive (H^δ+) charges.

As a result, in [NH₄ ]⁺, all N-H bonds are individually polar with an electronegativity difference of 0.84 units.

Dipole Moment

Dipole moment (μ) is a vector quantity that points from the positive pole to the negative pole of a bond or a molecule.

It is mathematically calculated as a product of the magnitude of charge (Q) and charges separation (r). The dipole moment is expressed in a unit called Debye (D).

The dipole moment of a polar covalent bond conventionally points from the positive center to the center of the negative charge.

So in polar bonds of [NH₄]⁺, the dipole moment of each N-H bond points from H^δ+ to N^δ- (as shown below).

Molecular geometry

According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, [NH₄]⁺ is an AX₄E₀ or simply AX₄-type molecular ion. To one N-atom at the center (A), four bonded atoms are attached (four H-atoms), and the central N-atom contains no lone pair (E).

The molecular geometry or shape of [NH₄]⁺ is tetrahedral, which is identical to its ideal electron pair geometry.

To minimize the repulsion and to attain stability in its tetrahedral structure, the bonded atoms in [NH₄]⁺ ion possess a bond angle of (∠H-N-H) 109.5°.

Due to the absence of any lone pair of electrons on the central N-atom, the [NH₄]⁺ ion has an identical molecular and electron geometry that is tetrahedral. The strongly electronegative N-atom attracts the shared cloud from each N-H bond. Hence, the N-H bonds are individually polar.

However, it is due to the symmetrical tetrahedral shape of [NH₄]⁺ that the net dipole moment of three upwards-pointing N-H bonds gets canceled with the dipole moment of a downwards-pointing N-H bond.

The electron cloud stays uniformly distributed as the dipole moments get canceled uniformly. Consequently, ammonium [NH₄]⁺ is overall a non-polar molecular ion (net µ = 0).

Difference between polar and nonpolar?

Polar molecule	Non-polar molecule
Atoms must have a difference in electronegativity	Atoms may have the same or different electronegativity values
Unequal charge distribution overall	Equal charge distribution overall
Net dipole moment greater than zero	Net dipole moment equals to zero
Examples include water (H2O), ethanol (CH3CH2OH), ammonia (NH3), sulfur dioxide (SO2), bromine trifluoride (BrF3), phosphorus trifluoride (PF3), nitrogen trifluoride (NF3), etc.	Examples include oxygen (O2), nitrogen (N2), methane (CH4), carbon disulfide (CS2), ethane (C2H6), ammonium ion [NH4]+, etc.

Also, check –

• NH₄⁺ lewis structure, molecular geometry, bond angle, hybridization
• How to tell if a molecule is polar or nonpolar?
• Is CH₂Cl₂ polar or nonpolar?
• Is CH₃F polar or nonpolar?
• Is NCl₃ polar or nonpolar?
• Is NO₃^– polar or nonpolar?
• Is BrF₅ polar or nonpolar?
• Is SF₄ polar or nonpolar?
• Is CO₂ polar or nonpolar?
• Is NH₃ polar or nonpolar?
• Is SO₂ polar or nonpolar?
• Is SO₃ polar or nonpolar?
• Is H₂O polar or nonpolar?
• Is H₂S polar or nonpolar?
• Is HCN polar or nonpolar?
• Is CCl₄ polar or nonpolar?
• Is XeF₄ polar or nonpolar?
• Is CH₂O polar or nonpolar?
• Is CHCl₃ polar or nonpolar?
• Is SF₆ polar or nonpolar?
• Is BF₃ polar or nonpolar?
• Is PCl₅ polar or nonpolar?
• Is CH₃Cl polar or nonpolar?

FAQ

Why is [NH4]+ a non-polar molecular ion?

[NH4]+ ion has four N-H bonds. The electronegativity difference between a bonded N-atom (E. N = 3.04) and H-atom (E. N= 2.20) is 0.84 units. Therefore, the N-atom gains a partial negative (δ–) charge while each H-atom gains a partial positive (δ+) charge. Each N-H bond thus possesses a particular dipole moment Hence, each N-H bond in [NH4]+ is individually polar. However, it is due to the symmetrical tetrahedral shape of [NH4]+ that the individual N-H dipole moments get canceled. The electron cloud stays uniformly distributed in the molecular ion overall. Thus, [NH4]+ is overall a non-polar molecular ion with net µ = 0.

Does [NH4]+ contain polar covalent bonds?

Yes, each N-H bond in the ammonium [NH4]+ ion is polar due to an electronegativity difference of 0.84 units between the bonded N-atom (E. N = 3.04) and H-atom (E. N= 2.20). Nitrogen more strongly attracts the shared electron cloud from each N-H bond as compared to hydrogen.

Why [NH4]+ is non-polar while NH3 is polar?

[NH4]+ has a symmetrical tetrahedral shape; the individual N-H dipole moments get canceled overall in the molecular ion. Hence, the electron cloud stays uniformly distributed in the molecular ion; thus, [NH4]+ is non-polar with a net dipole moment equal to zero. Contrarily, NH3 is an asymmetrical trigonal pyramidal molecule with a net dipole moment greater than zero, so it is a polar molecule. The dipole moments of individually polar N-H bonds do not get canceled equally in NH3, unlike NH4+.

How do you compare the polarity of NH4+ with N2H2?

The ammonium [NH4]+ ion is definitely non-polar (net µ = 0). It is due to the symmetrical tetrahedral shape of NH4+ that the dipole moments of individually polar N-H bonds get canceled uniformly on each side of the molecular ion. In contrast, there are two possibilities for diazene (N2H2). It also consists of polar N-H bonds. However, two geometrical isomers can be used to represent N2H2. Trans diazene is non-polar. A center of symmetry exits in the trans-form. The N-H dipole moments get canceled equally over this symmetrical center (net µ = 0). No such center of symmetry exists in cis-diazene. The N-H dipole moments do not get canceled equally in the bent shape of the molecule; thus, cis-diazene is overall polar (net µ > 0).

Is there a formal charge on the bonded atoms in the NH4+ molecule? Formal charge of an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)] For the central N-atom Valence electrons = 5 Bonding electrons = 8 Non-bonding electrons = 0 ∴ Formal charge on the central N-atom = 5 – 0 – 8/2 = 5 – 0 – 4 = 5 – 4 = +1 For H-atoms Valence electrons = 1 Bonding electrons = 2 Non-bonding electrons = 0 ∴ Formal charge on each H-atom = 1 – 0 – 2/2 = 1 – 0 – 1 = 1 – 1 = 0 In the [NH4]+ ion, each hydrogen atom obtains a formal charge equal to zero, while a +1 formal charge is present on the nitrogen atom. Hence overall charge present on the [NH4]+ ion is +1.

Summary

• Ammonium [NH₄]⁺ is a non-polar molecular ion.
• It consists of four polar N-H bonds.
• N-H bonds are highly polar due to an electronegativity difference of 0.84 units between the bonded N-atom (E. N= 3.04) and H-atom (E. N= 2.20).
• Ammonium [NH₄] ⁺ ion has a tetrahedral molecular and electron geometry with a bond angle of (∠ H-N-H) 109.5°.
• Due to the absence of any lone pair of electrons on the central N-atom, the [NH₄]⁺ ion has a symmetrical molecular shape, identical to its ideal electron pair geometry.
• The dipole moments of N-H bonds get canceled uniformly in this symmetrical tetrahedral shape leading to a net dipole moment μ in [NH₄]⁺ equals zero, so the ammonium ion is overall a non-polar molecular ion.