HOCN lewis structure, Characteristics:13 Facts You Should Know


In this article, we should discuss a moderately strong acid HOCN lewis structure and its characteristics facts in detail. Let’s start with the article.

Cyanic acid or HOCN lewis structure consists of electronegative radical cyanide. Due to the partial triple bond character present in cyanide, it has resonance stabilization. That makes the HOCN lewis structure a strong acid. H is attached here electronegative O atom and for this reason, the releasing of H in the HOCN lewis structure is very easy.

The shape of the HOCN lewis structure is linear, as the central C atom is sp hybridized. Due to sp hybridized this C has a more electronegative character. The bond angle is nearly 1800.

Some facts about HOCN

The physical state of cyanic acid is liquid. It has no characteristic color it is colorless. The molecule has a molar mass value of 43.025 g/mol. The boiling point and melting point of the nitrous acid are 296.6 K and 187 K respectively.

Cyanic acid can be prepared by the protonation of cyanate ions like the salt of alkali metal by the gaseous state of hydrochloric acid.

H+ + NCO = HOCN

It is also prepared by the thermal decomposition of a trimer of cyanuric acid.

C3H3N3O3 = 3 HOCN

1.    How to draw the HOCN lewis structure

As HOCN is a covalent molecule so we have to draw the HOCN lewis structure. With the help of the HOCN lewis structure we can predict the bond pair, lone pairs, and different covalent characters of HOCN.

HOCN lewis structure
HOCN Lewis Structure

Step 1–  In the first step of the HOCN lewis structure,  we have to calculate the valence electrons for the individual atoms which are present in the HOCN lewis structure and then added together to get the whole valence electrons for the HOCN lewis structure.

The first atom in the HOCN lewis structure is C which is a group IVA and P block element having electronic configuration [He]2s22p2. So, from its electronic configuration, we can see that the outermost shell for C is 2s and 2p orbitals and there are four electrons present. So, for C the valence electrons are four.

Now come for another atom N, which is group VA and also p block element and having electronic configuration [He]2s22p3. So, from the electronic configuration, it is evident that the valence shell for N are 2s and 2p orbitals and they contain five electrons so all the five electrons are valence electrons for N.

Another atom in the HOCN lewis structure is O, which is also a p block element. O is a group VIA element and its electronic configuration is [He]2s22p4. So, O has six electrons in the outer shell and those six electrons are the valence electrons for the O.

The last atom for the HOCN lewis structure is H and it has only one electron in its 1s orbital.

So, the total valence electrons present in the  HOCN lewis structure are 4+5+6+1 = 16 electrons.

Step 2- In the 2nd step, we have to select the central atom for the HOCN lewis structure based on size and electronegativity.

The size of C is the largest among all atoms in the HOCN lewis structure and the electronegativity of C is lesser than N and O. as we know from left to right across a period the size decreases, so C is larger than N and O. The size  H is very small, so keep all the consent C is considered the central atom of HOCN lewis structure.

Step 3-  Every s and p block element of the periodic table should obey the octet rule by completing their valence shell by accepting a suitable number of electrons and gaining stability like the nearest noble gas.

In the HOCN lewis structure, every atom is from the s and p block, so they have to obey the octet rule for gaining stability. The octet rule for the s clock element is complete their valence orbital by two electrons as the s orbital can occupy a maximum number of two electrons.

 For the p block elements, they have to complete their valence shell by eight electrons, as the p orbital can contain a maximum number of six electrons and every p block element can also contain an s orbital which can accumulate two electrons.

So, according to the octet rule, the electrons needed for the HOCN lewis structure for the stability are 2+(8*3) =26 electrons. but the valence electrons for the HOCN lewis structure are 16 electrons, so 26-16 =10 electrons are accumulated by 10/2 = 5 bonds. So, octet in HOCN lewis structure should be followed by the adding required number of bonds between atoms.

Step 4 – In this step, we should add the required number of bonds between the atoms in the HOCN lewis structure. There should be one bond between C and O and one bond between O and H. so the valency of O should be satisfied and the monovalency of H is also satisfied.

One bond between C and N, but the rest of the two bonds are also available and those two bonds are added between C and N, so the trivalency of N and tetravalency of C should be satisfied.

Step 5 – After adding the required number of bonds if any atoms in the HOCN lewis structure are not fulfilled its octet then we should add multiple bonds and add lone pairs if available.

 The valence electrons for O are six, and only two electrons are used for two bond formation so the rest of the four electrons are added to the O as lone pairs. N has five valence electrons after forming a triple bond it should contain lone pair.

Even there are triple bonds between c and N for completing their octet and valency.

2.    HOCN lewis structure shape

The shape of a very covalent molecule depends on the VSEPR theory and the surrounding atoms present in it. So, based on VSEPR theory and the surrounding atom the shape of the HOCN lewis structure is linear.

HOCN Shape

According to the VSEPR (Valence Shell Electrons Pair Repulsion) theory, if a molecule type of AX2 has no lone pairs over the central atom should adopt linear geometry with an 1800 bond angle, to get a stable structure. In the HOCN lewis structure, the linearity is also conserved due to the triple bond between C and N atoms, so the rigidity of the bond increases.

But the geometry around O atoms is slightly changed, as O has two pairs of lone pairs and is adopt net geometry like a water molecule, but concerning the central C atom, the shape of the molecule is linear. The shape of the molecule is also confirmed by the sp hybridization and bond angle value.

3.    HOCN valence electrons

Every covalent molecule has some number of valence electrons, and with the help of valence electrons we can predict the nature of bond angle, shape, and many more covalent characters should be predicted. In the HOCN lewis structure, the number of valence electrons is 16, which is the summation of individual atoms’ valence electrons.

The valence electrons for C are 4, as it is a group IVA element. The valence electrons for N and O atoms are 5 and 6 respectively as they are group VA and VIA elements. H has only one valence electron in its 1s orbital.

So, the total valence electrons present in the HOCN lewis structure is 1+4+5+6 =16 electrons.

4.    HOCN lewis structure lone pairs

Lone pairs are one kind of valence electrons, they are present in the valence shell of each atom but do not participate in the bond formation but can be satisfied by the octet rule count. In the HOCN lewis structure, N and  O contain lone pairs.

After adding the required number of bonds between all atoms in the HOCN lewis structure, we should check if all the atoms are satisfied by the octet or not.

N and O have five and six electrons respectively. But N formed a triple bond with C in the HOCN lewis structure, so the remaining two electrons of N exist as lone pair over the N atom.

O forms two single bonds with C and H atoms. O has six valence electrons so the rest of the four electrons exist in the valence shell as lone pairs, O Contains two pairs of lone pairs in its valence shell.

C is tetravalent and all the four electrons are used in the bond formation also for H one electron is used for bond formation with O. SO, H, and C have no lone pair in the HOCN lewis structure.

5.    HOCN lewis structure formal charge

HOCN is a neutral molecule but if there any kind of charge appears or not is predicted by the formal charge, which is a hypothetical concept considering the same electronegativity for every atom in the HOCN lewis structure.

Formal charge formula is, F.C. = Nv – Nl.p. -1/2 Nb.p.

Where Nv is the number of electrons in the valence shell or outermost orbital, Nl.p is the number of electrons in the lone pair, and Nb.p  is the total number of electrons that are involved in the bond formation only.

In the HOCN lewis structure, there are four different atoms are present so, we have to calculate the formal charge for every atom separately.

The formal charge of C is, 4-0-(8/2) = 0

The formal charge of N is, 5-2-(6/2) = 0

The formal charge of O is, 6-4-(4/2) = 0

The formal charge of H is, 1-0/(2/2) = 0

So, from the individual formula charge value, it is evident that there is no charge is appear in the HOCN lewis structure.

6.    HOCN lewis structure octet rule

Every atom in the molecule after bond formation should follow the octet rule by competing for their valence shell and gaining the nearest noble gas configuration. In the HOCN lewis structure, all the atoms present in it follow the octet rule.

The electronic configuration of C is [He]2s22p2, so it has two electrons in its p shell, but the p orbital can accumulate six electrons, so C needs six more electrons to complete its octet. C formed a bond with O and N by sharing electrons. It formed a four bond by sharing eight electrons involving its s and p orbital. So, after bond formation, it can complete its octet.

The electronic configuration of N is [He]2s22p3, so it needs three more electrons in its p orbital to complete its octet. N formed triple bonds with C, by sharing all the three electrons from its p orbital and its p orbital is filled by three bond pair and it has already a lone pair in its s orbital. Now it has eight electrons and it completes its octet.

In the case of O, it has an electronic configuration [He] 2s2p4. So, it needs two more electrons in its 2p orbital to complete six electrons in the valence shell. Those two electrons are accumulated by O via two bond formation and the rest of the electrons exist as lone pairs. So, O also completes its octet via bond formation.

H has only one electron and it formed with o via sharing one electron and completing its s orbital.

So, all the atoms in the HOCN lewis structure complete their octet by sharing electrons via a covalent bond.

7.    HOCN lewis structure angle

For the linear shaped molecule, the bond angle is normally 1800. So, the bond angle of the HOCN lewis structure is also 1800, as the HOCN lewis structure is also a linear molecule.

HOCN Bond Angle

The bond angle N-C-O is 1800 because the geometry around the central C atom is linear. The value of the bond angle is also predicted from the hybridization value of the central atom.

According to the VSEPR theory, the AX2 type of molecule should adopt linear geometry and if there is no deviation factor present then the bond angle is perfectly 1800. We can discuss it briefly in the hybridization section.

8.    HOCN lewis structure resonance

HOCN lewis structure itself is not a good resonating structure but its conjugate base cyanate is more resonance stabilized.so, we discuss the resonance structure of cyanate instead of the HOCN lewis structure.

HOCN Resonating Structures

All the above structures are the resonance structure of cyanate which is the conjugate base of the HOCN lewis structure. Among all the structures I is more stable as it contains a higher number of covalent bonds, also structure II has the same number of covalent bonds, but in structure I the negative charge is on the electronegative O atom, whereas in structure II the negative charge is on electropositive N atoms.

Structure III has a lower number of the covalent bond and positive charge on O and two negative charges on the N atom which is a destabilization factor.

9.    HOCN hybridization

In the HCON lewis structure, the central atom C is sp hybridized.

We used the formula to predict the hybridization of the HOCN lewis structure is,

H = 0.5(V+M-C+A), where H= hybridization value, V is the number of valence electrons in the central atom, M = monovalent atoms surrounded, C=no. of cation, A=no. of the anion.

The hybridization of central C in the HOCN lewis structure is, ½(4+0+0+0) = 2 (sp hybridized)

N and O both are not monovalent atoms.

Structure           Hybridization value  State of hybridization of central atom       Bond angle
Linear   2sp /sd / pd      1800
Planner trigonal3sp2                  1200
Tetrahedral      4sd3/ sp3      109.50
Trigonal bipyramidal5sp3d/dsp3               900 (axial), 1200(equatorial)
Octahedral      3sp3d2/ d2sp3              900
Pentagonal bipyramidal  7sp3d3/d3sp3                  900,720

      

From the hybridization value it is evident that if the number of hybrid orbital involed is equal to two then central atom should be sp hybridized.

Let’s understand the hybridization of C in details,

From the hybridization value, it is evident that we should only consider the sigma bond, not the π bonds.

Now we can calculate the bond angle from the hybridization value by bent’s rule.

According to Bent’s rule COSθ =s/s-1, where s is the % of s character in hybridization and θ is the bond angle.

In the sp hybridization, the % of s character is 50 or 1/2th.

COSθ = (1/2)/[(1/2)-1] = -1

Θ = 1800.

So, from the hybridization value, we can also predict the value of the bond angle for the HOCN lewis structure.

10.  Is HOCN polar or nonpolar

HOCN is a polar molecule.

Although HOCN is a linear and symmetric molecule, the two ends of the molecule are different so making the molecule is non-zero dipole-moment and also making the molecule polar.

11.  HOCN solubility

HOCN is soluble in,

  • Benzene
  • Water
  • Carbon tetrachloride
  • Diethyl ether

12.  Is HOCN soluble in water

Yes, HOCN is soluble in water.

HOCN is a polar molecule and water is also a polar protic solvent so it is obviously soluble in water (like dissolves like).

13.  IS HOCN a strong acid?

Yes, HOCN is a moderately strong acid.

The presence of more electronegative substituent makes the acid strong and also its conjugate base is highly resonance stabilized.

Conclusion

HOCN is a strong acid and a polar molecule. Cyanic acid also has a tautomer form name isocyanide acid and the character is almost the same.

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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