NO3 (Nitrate) is a tetrahedral compound having trigonal planar molecular geometry, making it a stable compound because of the presence of a double bond between one of the three N-O bonds. As the nitrates are highly soluble and biodegradable in nature, it is one of the most preferred fertilizers used around the globe.
As the toxicity level of nitrate is low, there has been a substantial disagreement about the risk against long-term exposure to nitrate. It might be interesting to know that even the nitrate (NO3) may not be harmful to human beings, it is a precursor of acid rain.
The atmospheric reactions of same are mentioned down below:
NO2 + O3 ——> NO3 + O2
NO2 + NO3 + (M) <==> N2O5
N2O5 + H2O(s) —–> 2 HNO3
NO2 + OH + M —–> HNO3 + M
It is always that studying the molecular geometry of nitrate makes students think about their polarity behavior. It is so because, even after having a double bond, covalent sharing of valence electrons, nitrate (NO3) is an exception to the rules of polarity molecules follow.
The exception is discussed as down below:
So, is NO3 polar or non-polar? NO3 is a non-polar molecule because of the symmetrical structure irrespective of the presence of a double bond, which cancels out all the dipole moments inside the molecule. As there is no net dipole moment, there will be no separation of charges between the two ends of the molecule and hence no polarity.
Why NO3 is a non-polar molecule?
Despite having a double bond in the structure, the non-polar behavior of the NO3 confuses many students. To understand this problem in the detail, we need to study the Lewis structure of NO3 first.
It is to be analyzed that irrespective of having a double bond between one of the three N-O bonds, all the three N-O bonds are located at an equal distance from one another making the three-dimensional structure symmetrical.
Through the valence shell electron pair repulsion theory (VSEPR) theory we know, the three symmetrical bonds and the O-N-O bond angle of 120° give rise to trigonal planar symmetry.
Hence, the NO3 molecule is symmetrical which in result becomes non-polar, as there is no separation of charges in a symmetrical molecule.
What are polar and non-polar molecules?
Polar molecules are asymmetrical molecules that have electric poles because of which separation of charges occurs at the ends. Where one end comprises of positive charge while the other gets collected by the negative only.
This separation of charges compels the molecule to strongly attract the other polar molecules nearby with the help of hydrogen bonds.
Moreover, it is this separation of charge which generates the net dipole moment on the molecule making it highly reactive.
One of the most suitable examples of polar molecules is Water (H2O). Read out the polarity of H2O.
Non-polar molecules, on the other hand, are symmetrical molecules that do not have electric poles because of which no separation of charges occurs at the ends. Due to this, there are no electric poles in the non-polar molecules and to undergo a bond formation with other molecules, weak Van der Waal interaction is formed upon.
Because of the formation of weak bonds and no charge distribution, the net dipole moment remains zero making non-polar molecules, weakly reactive.
One of the most prominent examples of non-polar molecules is Oil, as they do not readily with almost anything.
Check out the article written on the polarity of Oil.
What makes NO3 a non-polar molecule?
It is the presence of the negative charge on the overall NO3 molecule which makes the molecule non-polar in nature.
Irrespective of having three identical N-O bonds, there exists a delocalized electron system originating because of the combination of formal charges of oxygen with -2/3 of a charge and the nitrogen with +1 of a charge.
While we add up both the charges, (3* -2/3) + 1 = -1, we get -1 as the formal negative charge on one nitrate ion, making the NO3 molecule non-polar in nature.
Electronegativity of atoms in Nitrate (NO3)
Electronegativity is a mathematical way of determining the ability of an atom to attract shared electrons towards itself.
As the atom’s ability to attract, depends upon its atomic number and the distance at which valence electrons are available, the electronegativity is directly proportional to both the properties of an atom.
This means, higher the electronegativity number is, the more the atom will attract the shared electrons.
As the non-polar molecules do not attract shared electrons toward themselves, the electronegativity value tends to remain on the lower side.
For the non-polar molecules, the electronegativity difference between the two participating atoms must be lower than 0.5.
In the case of nitrate (NO3), the electronegativity value of nitrogen is 3.04 and that of oxygen is 3.44. The difference between both the values is 0.4 which is lower than 0.5, confirming that the NO3 molecule is non-polar in nature.
Why NO3 is not ionic but has a covalent bond?
Ionic bonds are generally formed between a metal and a non-metal where one donates the valence electrons while the other accepts them.
Whereas, the covalent bonds are generally formed between two non-metals where both the molecules share the valence electrons.
Usually, there exists some polarity in the covalent bonds because of the shared pair of valence electrons. But, nitrate (NO3) is one exception where besides having covalent bonds, the molecule is non-polar in nature.
From the above-mentioned Lewis structure, it can be seen that there is no complete transfer of valence electrons between the nitrogen and oxygen, participating atoms.
As there occurs a sharing of valence electrons, covalent bond forms in the NO3 molecule. In the case of ionic bonds, one atom loses the valence electrons completely to become a positively charged cation, whereas the other atom accepts those valence electrons to become negatively charged anions.
As this situation is not arising in the nitrate (NO3) molecule, so it is forming a covalent bond. It might be interesting to see know that, only by looking that the type of bond formation, the polar behavior of the nitrate (NO3) can be concluded upon.
How to determine the polar behavior of a molecule?
The polarity concept is dedicated to the covalent bonds and can be confirmed by studying the value of electronegativity of a molecule (which must be less than 0.4 to be non-polar).
Another method is of studying the molecular geometry through the valence shell electron pair repulsion theory (VSEPR) theory which helps with determining the structure and bond angle.
The industrial relevance of nitrate (NO3)
Even though nitrates are naturally occurring and of the least danger to human beings, in general, because of their highly oxidizing nature, nitrates are used to make explosives like gun powder, where explosion leads to oxidation of carbon and its compounds releasing a large number of gases.
Besides this, nitrates are also used as potential fertilizers in agriculture as they are highly biodegradable and can react with atmospheric gases to form another compound.
Nitrate (NO3) in news
Nitrate (NO3) being a precursor of acid rain, is a major reason for rock weathering occurring throughout the globe.
It has been recently figured out that the dual isotopic compositions; δ15N NO3- and δ18O-NO3- from the rainfall reached the groundwater because of the acid rain.
Nitrate (NO3) is a non-polar molecule due to the presence of a negative formal charge overall on the molecule.
Due to this negative charge, no polar ends form on the NO3 molecule and the molecule does not attract any other polar molecule.
This can be confirmed with the help of the valence shell electron pair repulsion theory (VSEPR) theory which says the molecular geometry of the NO3 molecule is trigonal planar with the O-N-O bond angle to be 120°. Such structure can give rise to non-polar molecules only.