NCO- Lewis Structure & Characteristics: 11 Complete Facts


NCO- is an ambidentate ligand that can coordinate with a different metal atom having a molecular mass of 41.053 g/mol.  Let us discuss the NCO- lewis structure in brief.

NCO- is an sp hybridized molecule with linear geometry having a negative charge present over N and O on basis of the electron resonance. It can donate electrons from either N or the O site, so it is known as an ambidentate ligand. So, it can bind from the N site as well as the O site also.

The nature of this ligand changes based on its coordination site. If it coordinates with metal via N then it is soft otherwise it can behave as a hard ligand. In this article, we should explore shape, angle, hybridization and many more about the NCO-.

1.     How to draw NCO- lewis structure

The lewis structure of NCO- gives us a clear idea of bonding mode detail. Now we should learn how to draw the NCO- lewis structure in few steps in the following section.

Counting the valence electrons

The total valence electrons for the NCO- are 16. This value of valence electrons is the summation of the individual valence electrons of the atoms. The valence electrons of N, C, and O are 5,4, and 6 respectively, which are confirmed by their electronic configuration. for negative charge one is added.

Choosing the central atom

It’s very important to select the central atom for a molecule to predict the geometry or other nature. On the basis of size and electronegativity, C is chosen as central in NCO-. The size of C is larger than N and O. Also, C is more electropositive than N and O.

Satisfying the octet

C, N, and O all the atoms are satisfied by the octet in the NCO-.  They all atoms complete their valence orbital by four, three, and two electrons respectively. The needs of electrons are decided by the availability of the valence electrons and all the atoms satisfied the octet by the eight electrons.

Satisfying the valency of each atom

After satisfying the octet we should check the stable valency of every atom in the NCO-. Nis trivalent, C is tetravalent and O is divalent. All the valency of the respective atoms is satisfied by the required number of bonds, ½[(8*3) -16] = 4 bonds. For the octet, needs of electrons are 8*3 =24.

Assign the lone pairs

After satisfying the octet and valency of each atom, if non-bonded electrons are remaining then they are assigned as lone pairs to the respective atoms.  C formed four bonds by its tetravalent so it has a lack of lone pairs, N and O contain one pair and three pairs of lone pairs after forming the bonds.

2.     NCO- lewis structure shape

The shape of the molecule is decided by the VSEPR theory and the hybridization value. Let us discuss about the NCO- shape in detail.

The shape of NCO- is linear. The geometry is dependent on the hybridization value. Also, as per VSEPR theory, AX2 molecules without lone pairs of central atoms always adopt linear geometry. The linearity is not disturbed because there is no repulsion.

NCO- Shape

The linear geometry is also maintained by the triple bond between N and C. So, there is no chance of free rotation of the bond around the central atom and the lone pairs of N and lone pairs of O are far away. So, there is no chance of deviation.

3.     NCO- valence electrons

The valence electrons are those electrons present in the outermost orbital of each atom. Now calculate the total valence electrons for the NCO- molecule.

The total valence electrons of NCO- is 16. This number is the total number of valence electrons that are present in the valence orbital of every individual atom present in the NCO- molecule. Each atom has a different number of electrons in their respective valence orbital and they are contributed.

Let us calculate the total valence electrons for the NCO-

  • The valence electrons for the C is 4
  • The valence electrons for the N is 5
  • The valence electrons for the O is 6
  • For negative charge, the electron count is 1
  • The total number of valence electrons for NCO- is 4+5+6+1 = 16

4.     NCO- lewis structure lone pairs

Lone pairs are the non-bonded electrons present in the outermost orbital of each atom but not involved in the bond. Now we learn about the lone pairs of NCO- in detail.

N and O contain lone pairs, and C lacks lone pairs. N and O have more electrons in the valence orbital after the bond formation. Those non-bonded electrons exist as lone pairs of that particular atom. C has only four electrons that are already involved in the bond formation so it has no lone pairs.

  • The lone pair of C is 4-4 = 0
  • The lone pair over N are 5-3 = 2 electrons which means 1 pair of lone pair.
  • The lone pairs over the O atom are 7 -1 = 6 electrons which means 3 pairs of lone pairs.
  • Due to the negative charge over O its valence electrons become 7.

5.     NCO- lewis structure angle

The bond angle is that particular angle which makes by the atoms present in a molecule to maintain the best geometry.  Let’s discuss the bond angle of NCO-.

The bond angle of NCO- around central atom C is 1800. The value of the bond angle also interns the hybridization value of the central atom. This is an AX2 type of molecule and for this type of molecule, the best bond angle is 1800 according to the VSEPR theory which makes the molecule linear.

NCO- Bond Angle

The value of the bond angle has merged with the geometry of the molecule which is linear. For linear molecules, the bond angle always is 1800. If there is no deviation factor present then the bond angle is always equal to 1800.

6.     NCO- lewis structure formal charge

The formal charge is a hypothetical concept for a molecule to check whether it is charged or neutral or which atom carries the charge. Let us calculate the formal charge of NCO-.

The formal charge of NCO- is not zero. Because there is already a negative charge present. Now we have to check by the formal charge formula which atom bears the negative charge. In the calculation of formal charge, we have to assume equal electronegativity for N, C, and O also.

The formula being used for the formal charge is, F.C. = Nv – Nl.p. -1/2 Nb.p.

  • The formal charge present over the N is 5-2-(6/2) =0
  • The formal charge present over the C is 4-0-(8/2) =0
  • The formal charge present over the O is 6-6-(2/2) =-1
  • So, from the above data, we can conclude that O contains the negative charge, but due to resonance the negative charge is replaced over N.

7.     NCO- lewis structure octet rule

The octet rule is the completion of the valence orbital atom by accepting suitable number of electrons to gain noble gas stability. Let us learn about the octet of NCO-.

To complete the octet N and C makes triple bonds between them. N, C, and O all are the p block element and according to the octet rule, they need eight electrons in the valence shell. From the electronic configuration of each atom, it is evident that C needs 4, N and O need 5 and 2 electrons respectively.

The stable valency of O is two, but here O formed one bond because it already carries a negative charge, so by forming one bond it can obey the octet. N and C follow octet by sharing electrons in their triple bonds.

8.     NCO- lewis structure resonance

By the concept of resonance, we can predict the delocalization of electron clouds among different skeleton forms. Now we learn more about the resonance of NCO-.

There is the possibility of resonance for the NCO- molecule. Because there is a triple bond and a negative charge already present so it can able to delocalize the negative charge between the double bond through different skeleton forms of the molecule.  The negative charge over O is more stable than N.

NCO- Resonating Structures

Structure I is the most stable and highest contributing structure because it has more number of covalent bonds and also O gets a negative charge. Structure II has also the same number of covalent bonds but N gets a negative charge and for III it has two negative charges over N which is the least favorable.

9.     NCO- hybridization

Hybridization is the mixing of atomic orbitals of different energy to form new hybrid orbital of equivalent energy. Let us understand the hybridization of NCO- in detail.

As NCO- is sp hybridized, the hybridization is presented in the following table.

Structure   Hybridization value State of hybridization of central atom     Bond angle
1. Linear    2sp /sd / pd 1800
2. Planner trigonal  3sp2       1200
3. Tetrahedral 4sd3/ sp3    109.50
4. Trigonal bipyramidal 5sp3d/dsp900 (axial), 1200(equatorial)
5. Octahedral  6sp3d2/ d2sp3     900
6. Pentagonal bipyramidal  7sp3d3/d3sp3     900,720
Hybridization Table

               

                                                      

NCO- Hybridization

From the above diagram, we can say that the s and one p orbital of C are involved in the hybridization, so the mode of hybridization is sp. Again, from the formula, H = 0.5(V+M-C+A), it is calculated that the hybridization value of C is 2 (sp). In the hybridization, consider the sigma bond, not the π bonds.

10. Is NCO- a solution?

A homogeneous mixture of two components in equal ratios maintaining a particle size less than 1 mm is called a solution. Let us see whether NCO- is the solution or not.

NCO- is not a solution because it is not a homogeneous mixture, here three types of elements are present. It is a ligand or molecule based on the reactivity center. It can be used as solute and gets soluble in a particular solution.

Why and how NCO- is not a solution?

NCO- is formed by the covalent interaction between C, N, and O atoms. It is a molecule or compound that can be soluble in different solutions under experimental conditions. So, it can behave as a solute for a particular solution. It is not a mixture rather it is a combination of three different elements.

11. Is NCO- ionic or covalent?

No molecule is pure covalent, it has some % of ionic character or vice versa – Fajan’s rule. Now discuss whether NCO- is covalent or ionic.

NCO- is a covalent molecule. The nature of the bond makes by the N, C and O are sharing electrons between them. Although there is a negative presence over the molecule but based on the ionic potential and polarizability we can say that NCO- is a covalent molecule.

Why and how NCO- is covalent?

NCO- is made by the sharing of electrons which makes it covalent. Let us explain below.

The ionic potential of the central C atom is very low, also the polarizability of N as well as O is very low. So, the anions were polarized by the cation. Lower the polarizability and ionic potential lower will be the ionic nature.

Although there is a charge present over the molecule, that negative charge is stabilized on the electronegative O atom because O has a greater affinity toward negative charge and it can draw the orbital electronegativity toward itself.

12. Is NCO- polar or non polar?

Whether a molecule is polar or not is dependent on the value of dipole-moment present in the molecule. Now discuss the polarity of the NCO- molecule.

NCO- is a non-polar molecule. The main reason behind its non-polarity is the shape of the molecule. The shape of the molecule is linear and due to the symmetric shape, there is no dipole moment existing in the molecule which makes a non-polar.

Why and how NCO- is non-polar?

The linear molecule is always non-polar due to its symmetric shape. Let us discuss the non-polarity of NCO- in the following section.

The cancellation of the dipole moment makes the value zero. The flow occurred from C to N and C to O, the direction of these two dipole-moment is just opposite because of the symmetric shape. The resultant of these two dipole-moment is nearly the same because the electronegativity of N and O are nearly equal.

Conclusion

NCO- is a non-polar covalent ambidentate ligand. Due to no -polar it has low solubility in water. It can bind from both sites to a metal center based on the oxidation of the metal center. Low oxidation metal prefers the N site whereas higher oxidation metal prefers the O site to bind and formed a stable metal-ligand complex.

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Biswarup Chandra Dey

Hi......I am Biswarup Chandra Dey, I have completed my Master's in Chemistry. My area of specialization is Inorganic Chemistry. Chemistry is not all about reading line by line and memorizing, it is a concept to understand in an easy way and here I am sharing with you the concept about chemistry which I learn because knowledge is worth to share it.

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