Is NH3 polar or nonpolar? - Polarity of NH3 (Ammonia)
Are you familiar with that pungent smell that comes when working near the fume hood of your chemistry laboratory? Well, that typical pungent odor belongs to a chemical compound called ammonia.
NH3 is the chemical formula for ammonia, a colorless bad-smelling gas. NH3 is a very important molecule with intriguing chemical properties and several useful applications. This article is about a very important chemical property of NH3 i.e., its polarity.
So, is ammonia (NH3) polar or nonpolar? Let’s find out.
Is NH3 polar or non-polar?
Ammonia (NH3) is a polar molecule. Nitrogen (N) is more electronegative than hydrogen (H), therefore, charges over the nitrogen and hydrogen atoms are unequally distributed, also, NH3 has an asymmetric trigonal pyramidal geometry, thus, there will be a net dipole moment in the molecule, therefore, it is a polar molecule.
A covalent bond between two unlike atoms in which the electron pair is unequally distributed between the bonded atoms is called a polar bond.
In this case, the atoms acquire a partial positive and a partial negative charge.
Same as, in NH3, the electron cloud is unequally distributed between Nitrogen and hydrogen atoms, because, there is a large difference of electronegativity exists between them.
What is the polarity of molecules?
Molecules containing polar bonds if attain a symmetrical shape such that the overall electron density gets balanced about a plane perpendicular to the center of the axis of the molecule, then such a molecule is overall non-polar.
Contrarily, asymmetric electron density forms polar molecules.
Why is NH3 polar?
Nitrogen is more electronegative than hydrogen so each N-H bond in NH3 is polar. The asymmetric trigonal pyramidal shape of NH3 further endorses that polarities of N-H bonds(their dipole) will not cancel out, therefore, NH3 is an overall polar molecule with a net dipole moment greater than zero.
Let’s read in detail the polarity nature of NH3.
Factors that determine the polarity of NH3
You might have guessed from the discussion above that there are three main factors that influence the polarity of all molecules namely:
Electronegativity
Dipole moment
Molecular geometry or shape
Let’s discuss each of these factors one by one and see how these apply specifically to ammonia (NH3) in confirming that it is a polar molecule.
Electronegativity
Electronegativity is the ability of an atom to attract a shared pair of electrons in a covalent bond.
Nitrogen is a highly electronegative (E.N= 3.04) than hydrogen (E.N = 2.2) atom.
There is an electronegativity difference of 0.84 units between these two atoms.
In NH3, three hydrogens (H) atoms are bonded to a central nitrogen (N) atom through single covalent bonds. Nitrogen has 5 valence electrons; it completes its octet while each hydrogen achieves a duplet electronic configuration through NH3 formation.
Nitrogen more strongly attracts the shared electron cloud from each N-H bond. N obtains a partial negative charge (Nδ-) due to a slight excess of electrons while each hydrogen attains a partial positive charge (Hδ+) due to a slight deficiency of electrons. Thus, each N-H bond is polar.
Dipole moment
Dipole moment (µ) is a vector quantity. It is a measure of separation between two oppositely charged atoms in a polar bond.
It is represented as a vector sign, pointing from the positive to the negative center, and is calculated in Debye (D) units.
µ = Q . r
Q = charge and r= bond length. 1 Debye = 3.34 x 10-30 C.m.
Considering the electronegativity difference between N and H atoms, each N-H bond in the NH3 molecule is polar with a dipole moment of 0.84 D. The dipole moment of each N-H bond points from Hδ+ to Nδ-. The net dipole moment of three N- H bonds will add up to give 1.4D
Molecular geometry or shape
NH3 has trigonal pyramidal geometry. The nitrogen (N) atom lies at the apex while the three hydrogens (H) are each situated at the corners of the pyramid which has a triangular base.
According to the VSEPR theory, NH3 is an AX3E-type molecule. There are three bond pairs (X) and one lone pair (E) of electrons around the central nitrogen atom (A).
The central N is sp3 hybridized so the ideal electronic geometry of NH3 is tetrahedral.
But the lone pair of electrons repel the bonded electron pairs in such a manner that NH3 obtains a distorted tetrahedral geometry or a trigonal pyramidal shape.
H-N-H bond angle decreases from the ideal 109.5° to 107.8°. The N-H bond length is equal to 101.7 pm.
Trigonal pyramidal is an asymmetric shape, therefore, the dipole moments of individual N-H bonds are enhanced (The net dipole moment of three N- H bonds will add up) so the net dipole moment of the overall NH3 molecule is greater than zero (1.46 D) and NH3 becomes a polar molecule.
Difference between polar and non-polar molecules
Polar molecule
Non-polar molecule
Atoms having 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 0
Net dipole moment equals to zero
Examples include water (H2O), ethanol (CH3CH2OH), ammonia (NH3) and sulfur dioxide (SO2), etc.,
Examples include oxygen (O2), nitrogen (N2), methane (CH4), and sulfur trioxide (SO3).
In NH3, individual bonds are polar because of nitrogen atom is more electronegative than the hydrogen atom, so, the dipole moment is from H to N.
The shape of NH3 is asymmetrical, therefore, the three dipoles directed from H to N will not cancel out.
The three dipoles in one direction form a net dipole moment. The net dipole moment of three N- H bonds will add up to give 1.46 D, therefore, ammonia (NH3) polar molecule.
Does NH3 contain polar covalent bonds?
Yes, each N-H bond in the ammonia (NH3) molecule is polar due to a difference in electronegativities of N and H atoms of about 0.84 Debye units.
Is NH3 a polar molecule?
“Yes, NH3 (Ammonia) molecule is polar in nature because of its asymmetrical shape ie; trigonal pyramidal structure, and the difference in electronegativities of N(3.04) and H(2.2).”
NH3 is a polar molecule with a net dipole moment of 1.4 D. Ammonia has three dipoles and these dipoles will not cancel out, they will add up in one direction, because, of the asymmetric shape of NH3. So, there will be some net dipole moment in the molecule, hence, NH3 is said to be a polar molecule.
How to know if a covalent bond is polar or not?
If the bonded atoms have an electronegativity difference between 0.5 and 1.6 then the covalent bond is polar. At an electronegativity difference below 0.5, the covalent bond is nonpolar.
Electronegativity difference greater than 2.0 leads to ionic bond formation involving a complete transference of electrons.
In an NH3 molecule, the electronegativity difference between nitrogen and a hydrogen atom is 0.84, so, the difference in electronegativity in the N-H bond is between 0.5 and 1.6, therefore, the bond in NH3 is a polar covalent type.
Why is NH3 polar but BF3 a non-polar molecule?
Both NH3 and BF3 have polar bonds present due to the electronegativity difference between the bonded atoms. But NH3 is an asymmetric trigonal pyramidal molecule while BF3 is a symmetrical trigonal planar molecule.
Individual bond polarities stay intact in NH3 while they get canceled in opposite directions in BF3. So, NH3 is a polar molecule (net dipole moment > 0). BF3 is a non-polar molecule (net dipole moment = 0).
Why is NH3 polar, and CCl4 not polar?
NH3 is an asymmetrical trigonal pyramidal molecule with a net dipole moment greater than zero, so, it is a polar molecule. On the other hand, CCl4 also has polar bonds present but unlike NH3 there is no lone pair of electrons on the central C atom. All four electron pairs are involved in bonding.
CCl4 forms the typical tetrahedral molecular geometry or shape with bond angles of 109.5 °. The dipole moments of C-Cl bonds get canceled in opposite directions thus CCl4 is a non-polar molecule overall with a net dipole moment = zero.
Is ammonia soluble in water (H2O)?
Like dissolves like. Ammonia (NH3) being a polar molecule is highly soluble in water (H2O), another polar molecule. NH3 can develop hydrogen bonding with H2O molecules.
What is the molecular geometry and shape of NH3?
NH3 forms a trigonal pyramidal shape due to the presence of a lone pair on nitrogen. H-N-H bond angles are 107.8 ° while the N-H bond length is 101.7 pm.
The central nitrogen in NH3 is sp3 hybridized. It forms sp3 – s sigma covalent bonds with hydrogen atoms.
Is there a formal charge present on NH3?
No formal charge is present on NH3. The valency or oxidation state of N in NH3 is -3 while that of each H is +1. 3 H atoms means 3 (+1) = +3.
+3 gets canceled with -3 thus 0 or no formal charge is present on NH3.
Why is ammonia more soluble in water than nitrogen (N2)?
NH3 can form hydrogen bonds with water. The highly electronegative N atom in NH3 molecules forms H-bonds with the hydrogens of H2O and vice versa the electronegative O atom of H2O forms H-bonds with the hydrogens of NH3.
N2 is a molecule composed of identical N atoms with no electronegativity difference.
It is non-polar and cannot dissolve in a polar solvent like water, additionally, it cannot form any hydrogen bonds thus NH3 is highly water-soluble while N2 is not.
Summary
Ammonia (NH3) is a polar molecule.
NH3 has polar bonds present. Nitrogen is more electronegative than hydrogen, it strongly attracts the shared electron pair from each N-H bond so each N-H bond in NH3 is polar.
NH3 has sp3 hybridization. It has three bond pairs and one lone pair of electrons thus an asymmetric trigonal pyramidal shape with bond angles of 107.8°.
Due to this unsymmetrical arrangement of atoms, NH3 is an overall polar molecule with a net dipole moment of 1.46 D.
Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/
Topblogtenz is a website dedicated to providing informative and engaging content related to the field of chemistry and science. We aim to make complex subjects, like chemistry, approachable and enjoyable for everyone.
Molecular geometry or shape
This article is really very helpful.
Thanks!