Orthonitrate (NO43-) ion Lewis structure, molecular geometry or shape, electron geometry, bond angles, formal charges, hybridization, polar or nonpolar
The chemical formula NO43- represents the orthonitrate ion, a unique oxyanion of nitrogen and conjugate base of orthonitric acid (H3NO4).
Sodium orthonitrate (Na3NO4) and potassium orthonitrate (K3NO4) are two common salts of the otherwise uncommon orthonitrate ion.
This implies that NO43- (molar mass = 78.006 g/mol) is a relatively unstable anion.
In this article, you will learn to draw the Lewis dot structure of NO43-. Moreover, we will also discuss the molecular geometry or shape of NO43-, its electron geometry, bond angles, hybridization, formal charges and polarity.
So for all this valuable information, continue reading!
The Lewis structure of the NO43- ion comprises a nitrogen (N) atom at the center. It is single-covalently bonded to three O-atoms and double-covalently bonded to the fourth O-atom at the sides. There is no lone pair of electrons on the central N-atom. However, the peripheral O-atoms carry 3 or 2 lone pairs, respectively, in the NO43-Lewis structure.
You can easily draw the Lewis dot structure of the orthonitrate ion with us by following the simple steps given below.
Steps for drawing the Lewis dot structure of NO43-
1. Count the total valence electrons present in NO43-
The two distinct elements present in NO43- are nitrogen and oxygen.
Nitrogen (N) is located in Group VA (or 15) of the Periodic Table of Elements, containing a total of 5 valence electrons in each N-atom.
In contrast, oxygen (O) is present in Group VI A (or 16) of the Periodic Table. Thus, it has a total of 6 valence electrons in each oxygen atom.
Total number of valence electrons in nitrogen = 5
Total number of valence electrons in oxygen = 6
The NO43- ion comprises 1 N-atom and 4 O-atoms.
An important point to remember is that the NO43- ion carries a negative three (-3) charge, which means 3 extra valence electrons are added in this Lewis structure.
∴ Therefore, the total valence electrons available for drawing the Lewis dot structure of NO43- = 1(5) + 4(6) = 29 + 3 = 32 valence electrons.
2. Find the least electronegative atom and place it at the center
By convention, the least electronegative atom out of all those available is chosen as the central atom while drawing the Lewis structure of a molecule or molecular ion.
The least electronegative atom can easily form covalent bonds with other atoms by sharing its electrons.
Nitrogen (E.N = 3.04) is less electronegative than oxygen (E.N = 3.44).
Therefore, the N-atom is chosen as the central atom in the NO43- Lewis structure, while the four O-atoms are spread around it, as shown below.
3. Connect the outer atoms with the central atom
In this step, the outer atoms, i.e., 4 O-atoms, are joined to the central N-atom using single straight lines.
A straight line represents a single covalent bond, i.e., a bond pair containing 2 electrons.
In the above structure, there are a total of 4 single bonds, i.e., 4(2) = 8 valence electrons are already consumed out of the 32 initially available.
Now let’s see in the next steps where to place the remaining 24 valence electrons in the NO43- Lewis dot structure.
4. Complete the octet of the outer atoms
An O-atom needs a total of 8 valence electrons in order to achieve a stable octet electronic configuration.
An N-O bond represents 2 valence electrons already present around each of the four oxygen atoms.
Therefore, to complete its octet, the remaining 6 valence electrons are placed as 3 lone pairs on each O-atom, as shown below.
5. Complete the octet of the central atom
Total valence electrons used till step 4 = 4 single bonds + 4(electrons placed around each O-atom, shown as dots) = 4(2) + 4(6) = 32 valence electrons.
Total valence electrons – electrons used till step 4 = 32 -32= 0 valence electrons.
As all the valence electrons initially available for drawing the NO43- Lewis structure are already consumed so there is no lone pair of electrons on the central N-atom.
The good thing is that the central N-atom already has a complete octet as per four N-O single bonds, i.e., 4(2) = 8 valence electrons surrounding it.
But is this Lewis structure stable? Let’s find out in the next step by applying the formal charge concept.
6. Check the stability of Lewis’s structure using the formal charge concept
The less the formal charge on the atoms of a molecule or molecular ion, the better the stability of its Lewis structure.
The formal charges can be calculated using the formula given below.
Formal charge = [valence electrons- nonbonding electrons- ½ (bonding electrons)].
Now let us use this formula and the Lewis structure obtained in step 5 to determine the formal charges present on the NO43- bonded atoms.
As per the calculation shown above, in the Lewis structure drawn till yet, the central N-atom carries a +1 formal charge while each of the 4 O-atoms carries a -1 formal charge. +1 + 4(-1) makes a total of -3, i.e., the overall charge present on the orthonitrate anion.
But as discussed already, the lower the formal charges on individually bonded atoms, the greater the stability of a Lewis structure.
So now let’s see how we can reduce the formal charges on NO43- bonded atoms by converting a lone pair into an additional covalent chemical bond.
7. Minimize formal charges by converting a lone pair into a covalent bond and again check the stability of Lewis’s structure
To reduce the formal charges, a lone pair from one of the four terminal O-atoms is converted into an additional covalent bond between the central N-atom and the corresponding O-atom, as shown below.
This results in a total of 10 valence electrons surrounding the central N-atom in the NO43- Lewis structure which apparently violates the octet rule. However, the orthonitrate ion is an exception and thus acceptable.
The hyper valency of NO43- is better explained by the molecular orbital theory (MOT) of chemical bonding.
MOT states that electrons keep revolving throughout the molecule, which overpowers the claim of particular atomic orbitals holding a set number of electrons.
Now let us again check the stability of NO43- Lewis structure by applying the formal charge concept.
For nitrogen atom
Valence electrons of nitrogen = 5
Bonding electrons = 3 single bonds + 1 double bond = 3(2) + 4 = 10 electrons
Non-bonding electrons = no lone pair = 0 electrons
The above calculation shows that the formal charges present on the central N-atom and N=O bonded O-atom are reduced to zero.
Contrarily, a -1 formal charge is present on each single-bonded O-atom, leading to an overall formal charge of 3(-1) = -3 on the orthonitrate (NO43-) Lewis structure.
Also, note that any one O-atom out of all four available can form a double bond with the central N-atom in NO43- Lewis structure. Consequently, the following resonance structures are possible for representing the orthonitrate ion.
The actual NO43- structure is a hybrid of all the possible resonance forms, known as the resonance hybrid.
Now let us discuss the molecular and electron geometry of NO43-.
What are the electron and molecular geometry of NO43-?
The molecular geometry or shape of orthonitrate (NO43-) is identical to its ideal electronic geometry, i.e., tetrahedral. The absence of any lone pair of electrons on the central N-atom implies that no distortion is witnessed in the molecular ion’s shape and geometry.
Molecular geometry of NO43-
The molecular geometry or shape of the orthonitrate (NO43-) ion is tetrahedral.
There is no lone pair of electrons on the central N-atom in the NO43- ion. Thus, no lone pair-lone pair or lone pair-bond pair electronic repulsions exist in the molecular ion. The oxygen atoms bonded to the central N-atom occupy positions such as the four corners of a regular tetrahedron, as shown below.
Electron geometry of NO43-
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, the ideal electronic geometry of a molecule or molecular ion containing 4 electron density regions around the central atom is tetrahedral.
Four N-O bonds and no lone pair make a total of 4 electron density regions surrounding the central N-atom in NO43-. Hence its electron geometry is also tetrahedral.
An easy trick to finding a molecule’s electron and molecular geometry is using the AXN method.
AXN is a simple formula representing the number of bonded atoms and lone pairs present on the central atom.
It is used to predict the shape and geometry of a molecule or molecular ion using the VSEPR concept.
AXN notation for NO43-
A in the AXN formula represents the central atom. In NO43-, a nitrogen (N) atom is present at the center, so A = N.
X denotes the atoms bonded to the central atom. In NO43-, 4 O-atoms are directly bonded to the central N-atom. So X = 4 for NO43-.
N stands for the lone pairs present on the central atom. As per the Lewis structure of NO43-, the central N-atom has no lone pair of electrons. Thus, N = 0 for NO43-.
As a result, the AXN generic formula for NO43- is AX4N0 or simply AX4.
Now, you may have a look at the VSEPR chart below.
The VSEPR chart confirms that a molecule or molecular ion with an AX4 generic formula is identical to its electron geometry, i.e., tetrahedral, as we already noted down for the orthonitrate (NO43-) ion.
Hybridization of NO43-
The central N-atom is sp3 hybridized in NO43-.
The hybridization present in a molecule or molecular ion can be determined using its steric number against the table given below.
The steric number of the central N-atom in NO43- is 4, so it has sp3 hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The bond angles of NO43-
The ideal bond angle in a tetrahedral molecule is 109.5°. Therefore, all O-N-O bond angles equal 109.5° in the NO43- ion. Conversely, each N-O bond length equals 139 pm in the orthonitrate ion.
As per Pauling’s electronegativity scale, a polar covalent bond is formed between two dissimilar atoms with an electronegativity difference between 0.4 and 1.6 units.
An electronegativity difference of exactly 0.4 units is present between the covalently bonded atoms in each N-O bond of NO43-.
Therefore, all four covalent chemical bonds present in the orthonitrate anion are individually polar.
However, it is due to the symmetrical tetrahedral shape of the orthonitrate ion that the net effect of three downwards-pointing N-O dipole moments gets canceled with an upwards-pointing N=O dipole moment.
The charged electron cloud stays uniformly distributed, which leads to an overall non-polar molecular ion, i.e., NO43- (net µ = 0).
What is the molecular shape of the unfamiliar orthonitrate (NO43-) ion?
The molecular geometry or shape of the orthonitrate (NO43-) ion is tetrahedral. Four O-atoms are covalently bonded to the central N-atom like four vertices of a tetrahedron.
There is no lone pair of electrons on the central N-atom; thus, no distortion is present in its overall molecular shape.
Is the shape of NO43- ion the same as its electron geometry?
Yes. The orthonitrate (NO43-) ion possesses an identical electron and molecular geometry or shape, i.e., tetrahedral.
The absence of any lone pair of electrons on the central N-atom implies that no lone pair-lone pair or lone pair-bond pair electronic repulsions exist in NO43-. Thus, its molecular geometry and shape stay undistorted.
How does the shape of nitrate (NO3–) ion differ from that of orthonitrate (NO43-)?
In contrast, the shape of NO43- is tetrahedral as four O-atoms are covalently bonded to the central N-atom.
How is the shape of NH4+ similar to that of NO43-?
Both NH4+ and NO43- possess a similar tetrahedral shape.
To a nitrogen atom at the center, four atoms are attached like four corners of a tetrahedron, and there is no lone pair of electrons on the central N-atom.
How are the shapes of nitrite (NO2–) and orthonitrate (NO43-) ions the same or different?
The molecular shapes of the nitrite and orthonitrate ions are quite different from each other.
In NO2–, two O-atoms are directly attached to an N-atom at the center. There is 1 lone pair of electrons on the central N-atom, which leads to strong lone pair-bond pair electronic repulsions.
The molecular ion thus occupies a bent, angular, or V-shape, unlike the tetrahedralshape ofNO43-which contains no lone pair on the central N-atom.
The total number of valence electrons available for drawing the orthonitrate (NO43-) ion Lewis structure is 32.
The molecular geometry or shape of NO43- w.r.t the central N-atom is identical to its ideal electronic geometry, i.e., tetrahedral.
The central N-atom is sp3 hybridized in NO43-.
NO43- is a non-polar molecular ion as the equal and opposite N-O dipole moments get canceled uniformly.
Zero or no formal charges are present on the central N-atom or the N=O bonded O-atom in NO43- while the other three O-atoms carry a formal charge of -1 each.
3(-1) makes an overall charge of -3 on the orthonitrate ion, ensuring we have drawn the NO43- Lewis structure correctly in this article.
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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