Have you ever done an experiment where you dip a flower in a cold substance and shatter it on a table like glass? That was liquid nitrogen. Even the foods you eat that can last for a long time was undoubtedly preserved with nitrogen gas. However, when we look at the chemical structure of N2, a common question a new chemist may have is if N2 is polar or nonpolar. Let’s explore a few topics about N2’s structure and reactivity to find the answer!
So, is N2 polar or nonpolar? N2 is a nonpolar molecule because of its linear geometrical structure and it is a diatomic molecule. As a result, both atoms have equal electronegativity and share an equal proportion of charge and the overall molecule result in a net-zero dipole moment making it a nonpolar molecule.
Nitrogen, or N2, is a very abundant and necessary chemical for biological life and industrial processes. Nitrogen makes up 78% by volume of the air we breathe every day, and it is found in compound form in all living things.
Nitrogen is also plentiful in industrial chemistry, including fertilizers, dyes, nylon, and explosives. Most commonly, any cleaning supplies you’ve used with ammonia, NH3, was made with molecular nitrogen.
Polarity Based on Electronegativity
When atoms form bonds to create molecules, we can determine the level of polarity the molecule will exhibit. Ionic bonds completely transfer valence electrons between atoms to form a charge for both atoms.
For example, when sodium (Na) bonds with chlorine (Cl), sodium gives up its one valence electron to chlorine, forming Na+and Cl-, the most stable form of these atoms.
However, we’re discussing covalent bonds, which share electrons between atoms. These bonds occur between nonmetals, and covalent bonds can either be polar or nonpolar.
When covalent bonds occur, there is a transfer of electron density from one atom to another. If the electronegativities of the atoms are not equal, the electrons will not be shared equally, forming partially ionic charges on each atom.
A great example of this is the formation of hydrochloric acid or HCl.
Electronegativities are typically provided for the element you are using, so I will provide them here. Hydrogen (H) has an electronegativity of 2.1, while Chlorine (Cl) has an electronegativity of 3.0; the higher the electronegativity, the more negative an atom will be when it’s stable.
Hydrogen has one valence electron and wants two to complete its valence shell; chlorine has seven electrons and wants eight to complete its valence shell. Thus, they will share their one electron, forming a covalent bond.
However, the chlorine will take up more electron density since its electronegativity is higher than that of hydrogen.
This means chlorine is going to show a partial negative charge from its increased electron density. Conversely, hydrogen develops a partial positive charge due to its lack of electron density.
This creates a dipole moment, which directs the electron density to the more electronegative molecule.
Therefore, a hydrochloric acid molecule is going to be polar because there is a difference in electronegativities and a molecular dipole moment.
Here is the article to check out the polarity of HCl.
Why is N2 a nonpolar molecule?
Let’s apply this logic to N2. Nitrogen atoms have an electronegativity of approximately 3.04. But in nitrogen gas, it is a homonuclear molecule, meaning it is two of the same atoms bonded together.
There would be no difference in electronegativity between the two nitrogen atoms, which means they would share electron density equally.
If the electron density is shared equally between the two atoms, no dipole moment can form. Thus, we can assume that N2 is nonpolar.
Lewis structure of N2
A Lewis Structure is a very simple representation of the valence, or outermost, electrons in a molecule. It does not explain the geometry of the molecule, but it is a step forward in approaching the geography.
But to find out if N2 is polar or nonpolar, the Lewis Structure can reveal the best electron makeup of the molecule.
Nitrogen is a member of the Group 5A on the periodic table, meaning its outermost shell has five electrons. The Lewis structure of a single nitrogen atom is below.
Nitrogen, like most elements on the periodic table, follows the octet rule, meaning it wants eight electrons in its outer shell.
So, it will seek out other atoms that also want to complete the octet rule so they can share valence electrons. For example, Ammonia is a compound made of one nitrogen and three hydrogen molecules.
The goal is to create electron pairs: at the top of the lewis structure for a nitrogen atom, there is already a pair of electrons or a lone pair, so they are not available for bonding.
The other three single electrons are available to make covalent bonds or bonds that share the electrons between two atoms, with other atoms that have single electrons.
Hydrogen has one electron, and only needs two electrons to complete its outer shell; thus, nitrogen has room for three hydrogen atoms.
As shown below, Nitrogen now has eight electrons surrounding it, in the form of one lone pair and three single bonds.
Now nitrogen’s octet rule is complete, and hydrogen has the two electrons needed for a complete valence shell.
This leaves us with Ammonia’s Lewis structure, which matches its molecular formula, NH3. Check out the article for the polarity of NH3.
Now let’s take nitrogen’s molecular formula, N2. Nitrogen is a diatomic molecule, which means at standard temperature and pressure (1 atm at 25°C), Nitrogen atoms naturally bond with another nitrogen atom to fulfill both atom’s octet rule.
Nitrogen exists in this family with other diatomic molecules, such as oxygen, hydrogen, and the four halogens (fluorine, chlorine, iodine, and bromine). So, what is N2’s Lewis Structure?
Well, remembering that nitrogen has five valence electrons, with two of these electrons forming a lone pair, they need to complete the octet rule by binding their other three free electrons.
As shown in the figure above, one electron from one nitrogen molecule will form a single bond with another electron from the other nitrogen.
For both nitrogen atoms to fulfill the octet rule, all three of the free electrons will form bonds, creating a triple bond. Thus, a nitrogen molecule exists in nature with a triple bond, making it low in energy and stable in nature.
Molecular Geometry of N2
Now that we’ve covered the Lewis structure, we can explore the molecular geometry for N2.
You can typically predict the structure of the molecule from the Lewis Structure, but the Lewis structure can direct us to the valence-shell electron-pair repulsion, or VSEPR theory.
VSEPR theory works on the assumption that a molecule’s geometry will minimize the repulsion between electrons in a valence shell of that atom.
Remember that electrons are negative, and, much like magnets, they will repel each other if they get too close to one another, creating a strain on the molecule. So, we want to minimize that strain.
We know that nitrogen gas exists as a diatomic molecule, and the Lewis Structure shows only two atoms participating in its structure.
According to VSEPR theory, the only structure N2 could take is linear, or just a straight line. This means that the two atoms are apart at a 180° angle., as seen below.
Typically, linear molecules will be nonpolar, but that is not always the case (see: hydrochloric acid, hydrofluoric acid, carbon monoxide), so we cannot assume N2 to be nonpolar on this alone.
For this, we will have to dive a little deeper into electron density and electronegativity as discussed above already.
Nitrogen as a compound is tremendously abundant in our every day lives. As a diatomic, homonuclear molecule, we can determine its polarity from its structure, geometry, and electron density.
We found that nitrogen gas forms a strong triple bond, is linear in geometry with 180° between nitrogen atoms, and shares its electron density equally among nitrogen atoms. Therefore, we can determine that nitrogen gas is nonpolar.