NF3 is the chemical formula for nitrogen trifluoride. It is a synthetic inorganic chemical formed by the reaction of HCl with NH3 and has a molar mass of 71 g/mol. NF3 is toxic, odorless, colorless, and non-flammable gas. It is primarily used in manufacturing semiconductor devices such as LCD displays, thin-film solar cells, etc.
To find out whether the nitrogen trifluoride (NF3) molecule is polar or non-polar, continue reading this article.
Is NF3 polar or non-polar?
Nitrogen trifluoride (NF3) is a polar molecule. NF3 consists of a nitrogen (N) atom and three fluorine (F) atoms. The nitrogen atom is present at the center of the molecule, while three fluorine (F) atoms occupy terminal positions, one on each side, making a trigonal pyramidal molecular shape.
An electronegativity difference of 0.94 units exists between nitrogen and fluorine atoms in each N-F bond in the NF3 molecule. Thus, all three covalent bonds are individually polar in NF3 and possess a specific dipole moment value (symbol µ).
The asymmetrical trigonal pyramidal shape and geometry of NF3 further enhance the polarity effect. The N-F dipole moments do not get canceled. The electron cloud distribution does not stay uniform thus, NF3 is overall polar (net µ =0.24 D).
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 nitrogen trifluoride (NF3) molecule is overall polar.
Factors affecting the polarity of NF3
Electronegativity
It is defined as the ability of an atom to attract a shared pair of electrons from a covalent chemical bond.
Electronegativity decreases down the group in the Periodic Table of elements while it increases across a period.
Greater the electronegativity difference between bonded atoms in a molecule, the higher the bond polarity.
Nitrogen (N) is present in Group V A (or 15) of the Periodic Table. The electronic configuration of nitrogen is 1s2 2s2 2p3. As per this 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 a nitrogen atom can achieve a complete octet electronic configuration.
Conversely, fluorine (F) is a halogen that belongs to a Group of VII A (or 17) of the Periodic Table. The electronic configuration of a fluorine atom is 1s2 2s2 2p5. Valence electrons in fluorine are total 7 in number. Therefore, an F-atom has a deficiency of only a single electron to complete its octet.
Hence in NF3, three F-atoms are single covalently bonded with the central N-atom, one on each side of the trigonal pyramidal shape. In this way, all four bonded atoms attain a complete octet configuration via chemical bonding in NF3.
One lone pair of electrons is present on the nitrogen atom that tries to repel the bonded pairs of electrons. Consequently, the adjacent atoms are pushed apart giving NF3 a trigonal pyramidal shape and geometry.
Atom
Electronic configuration
Valence electrons
Nitrogen (7N)
1s22s22p3
5
Fluorine (9F)
1s2 2s2 2p5
7
The electronegativity of the F-atom is 3.98 and of N-atom is 3.04. The electronegativity difference of 0.94 units is present between the bonded N-atom and F-atoms.
The more electronegative F-atom strongly attracts the shared electron cloud away from the central N-atom in each of the N-F single bonds present in NF3.
Thus, the nitrogen atom present at the center of NF3 gains a partial positive (Nδ+) charge, while each terminal fluorine atom obtains a partial negative (Fδ-) charge. As a result, each N-F bond is individually polar in the nitrogen trifluoride molecule.
Dipole Moment
The dipole moment is the product of electrical charge (Q) and bond length (r) between two bonded atoms. It is a vector quantity expressed in Debye (D) units.
It is represented by a Greek symbol µ and measures the polarity of a bond.
The dipole moment of a polar covalent bond conventionally points from the positive center to the center of the negative charge. So in NF3, the dipole moment of each N-F bond points from Nδ+ to Fδ- (as shown below).
Molecular geometry
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, NF3 is an AX3E1 molecule. To one N-atom at the center (A), three F-atoms (X) are attached, and there is one lone pair (E) on the central atom.
A lone pair of electrons on the central N-atom leads to strong lone pair-bond pair repulsions in addition to the N-F bond pair-bond pair repulsive effect. The strong repulsive effect distorts the shape and geometry of the molecule.
Thus, NF3 adopts an asymmetric trigonal pyramidal shape and molecular geometry. Each F-N-F bond angle is 101.9° in NF3.
It is due to this asymmetrical shape that the dipole moments of individually polar N-F bonds do not get canceled. The electron cloud stays non-uniformly distributed over the molecule. Thus, NF3 is overall polar (net µ = 0.24 Debye).
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), nitrogen trichloride (NCl3), nitrogen trifluoride (NF3), etc.
Examples include oxygen (O2), nitrogen (N2), methane (CH4), nitrate [NO3]– ion, etc.
NF3 has polar covalent bonds present due to a specific electronegativity difference of 0.94 units between the bonded nitrogen (E. N=3.04) and fluorine (E. N=3.98) atoms in each N-F bond.
NF3 is an asymmetrical trigonal pyramidal molecule. So the dipole moments of individually polar N-F bonds do not get canceled enhancing the polarity of the molecule.
Thus, NF3 is overall polar with the net dipole moment of µ = 0.24 Debye.
What causes the NF3 molecule to be trigonal pyramidal in shape, and how this shape affects the molecular polarity?
Bond polarity depends on the electronegativity difference between bonded atoms, while molecular polarity is governed by the overall shape of the molecule.
In NF3, there is a lone pair of electrons on the central N-atom that distorts the shape and geometry of the molecule.
It thus adopts an asymmetric trigonal pyramidal shape, which leads to an unequal charge distribution overall, thus contributing to overall molecular polarity.
Why NF3 is polar, but BF3 a non-polar molecule?
Nitrogen trifluoride (NF3) has an asymmetricaltrigonal pyramidal The dipole moments of individually polar N-F bonds do not get canceled in NF3; thus, it is polar (net µ > 0).
Zero formal charges is present on the central N-atom and also on each of the terminal F-atoms.
Thus, the overall charge present on the nitrogen trifluoride molecule is Zero.
Summary
Nitrogen trifluoride NF3 is a polar molecule.
It consists of polar N-F bonds due to the electronegativity difference of 0.94 units between nitrogen and a fluorine atom.
Nitrogen trifluoride NF3 has an asymmetrical trigonal pyramidal shape with a 101.9° bond angle due to a lone pair of electrons on the central N-atom in NF3.
The dipole moments of individually polar N-F bonds do not get canceled due to this asymmetrical shape.
The net dipole moment in NF3 is 0.24 Debye, so it is overall polar.
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/
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