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

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is nh4+ polar or nonpolar

[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 moleculeAmmonium [NH4]+
Bond typePolar covalent
Molecular geometryTetrahedral
Polar or Non-polar?Overall Non-polar
Dipole moment0
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.

Nonpolar vs polar molecule

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]+.

What is NH4+ lewis structure

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 present in NH4+

AtomElectronic configurationValence electrons
Nitrogen (7N)

1s2 2s2 2p3

5
Hydrogen (1H)1s11

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 (Nδ-) charge while the hydrogen atoms in its surroundings obtain partial positive (Hδ+) charges.

NH4+ dipole charges

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

N-H bond is polar in NH4+

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).

what is dipole moment representation

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 Hδ+ to Nδ- (as shown below).

individual dipole moment of NH4+

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.

Why is NH4+ nonpolar molecule

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 moleculeNon-polar molecule
Atoms must have a difference in
electronegativity
Atoms may have the same or different electronegativity values
Unequal charge distribution overallEqual charge distribution overall
Net dipole moment greater than zeroNet 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 –

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+.

NH4+ is nonpolar but NH3 is polar

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.

polarity of NH4+

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).

polarity of N2H2

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.
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