FCN Lewis Structure, Characteristics : 19 Facts You Should Know

This article shall discuss FCN lewis structure, its characteristics, ways to represent lewis dot structure and other relevant facts.

FCN lewis structure, also known by the chemical name as cyanogen fluoride, is an inorganic molecule with a molecular weight of 45.016 g/mol.

Some facts about FCN lewis structure :

  • Molar mass/Molecular weight = 45.016 g/mol.
  • Boiling point = -46.17 0C , Melting point = – 82 0C .
  • Colorless and possesses pungent smell.
  • Toxic gas.
fcn lewis structure
3D representation of FCN lewis structure (cyanogen fluoride) from wikipedia

FCN lewis structure :

FCN Lewis structure or Lewis dot structure is an electronic representation of a molecule representing its bonds orientation along with the formal charge acquired by each constituent atom comprising the molecule.

In short, it briefs about the molecular representation. Knowing the lewis dot structure of a molecule is the first and foremost step towards decoding the physical and chemical properties and characteristics of a molecule.

Steps to draw a Lewis Structure of FCN :

  • The first step involves counting total number of electrons available. Fluorine atom ( F ) belongs to 17th group of the periodic table and contains 7 total valence electrons. Carbon atom belongs to group 14th ( C ) and has a total of 4 valence electrons and Nitrogen atom ( N ) belongs to group 15th and has a total of 5 valence electrons. This makes a total of 16 valence electrons available from each constituent atoms to construct FCN Lewis Structure.
  • The next step involves choosing the central atom based on their electronegativity difference. The least electronegative C atom with X = 2.55  is chosen as the central atom. F has electronegativity X = 3.98 and N has electronegativity X = 3.04 ( X = Magnitude of electronegativity difference )
  • Each constituent atom tries to accommodate 8 electrons in its surrounding to comply the octet rule. Firstly, all the atoms with its respective valence electrons are drawn. Next, each atom is aligned in a way that they can accommodate 8 electrons around themselves and with the neighbouring atoms by either sharing electrons covalently or datively.
  • C is tetravalent in nature and it forms 4 bonds with the other two atoms. It shares 4 of its valence electrons with F and N. N shares 3 of its valence electrons forming a triple bond with C and remaining two electrons stay as lone pair of electrons on N. F shares 1 valence electron with C forming a single bond and remaining 6 valence electrons stay as lone pair of electrons on F.
  • In doing so, we get a linear shaped cyanogen fluoride molecule that follows octet rule dutifully.

Schematic representation of FCN is shown below :

FCN Lewis structure

FCN lewis structure resonance :

Resonance structures are other representation of lewis dot structure showing all the possibilities of electronic distributions, those representation that acquires the highest energy and those which attains the lowest stable energy is well observed through resonance.

Since the triple bond involves a pi electron cloud that can get delocalized, hence FCN lewis structure shows resonance.

One of the pi bonds get delocalized on N atom resulting in a negative charge and the C acquires a positive charge. The overall charge separation is zero due to charge cancellation and attaining neutrality.

FCN lewis structure resonance.

FCN lewis structure shape :

FCN lewis structure adopts a linear shape. This is in accord with VSEPR theory. Since C has sp hybridization, it is most stable as all the electrons are at maximum distance from one another i.e., at 1800 angle.  

The structure is shown in FCN hybridisation section.

FCN hybridization :

Ground state electronic configuration of C: [He]2s22px12p1y2pz

Excited state electronic configuration of C: [He]2s12px12p1y2p1z

Ground state electronic configuration of F : [He]2s22px22p2y2p1z       

Ground state electronic configuration of N : [He]2s22px12p1y2p1z

C undergoes sp hybridization where two of the four unpaired electrons in the excited state pair up with N and F. They form sigma bonds by bonding and overlapping along their internuclear axis.

The remaining two unpaired electrons in the unhybridized p subshells of C forms two pi bonds by sidewise overlapping with the unshared pi electron cloud of nitrogen. F undergoes sp3 hybridisation with C forming a sigma bond and the remaining 6 electrons stay as 3 lone pairs of electrons on F atom.

FCN lewis structure hybridisation.

FCN valence electrons :

Ground state electronic configuration of C: [He]2s22px12p1y2pz

Ground state electronic configuration of F : [He]2s22px22p2y2p1z       

Ground state electronic configuration of N : [He]2s22px12p1y2p1z

Valence electrons are the outermost electrons residing in the subshells that participates in chemical bond formation or ionization.

Here, C has 4 valence electrons. F has 7 valence electrons. N has 5 valence electrons

Therefore, FCN lewis structure has a total of 16 valence electrons.

FCN lewis structure lone pairs :

FCN lewis structure has a total of 4 lone pairs of electrons. 3 lone pairs of electrons reside on F atom and 1 lone pair resides on N atom.

Lone pairs of electrons are those valence electrons that do not participate in any covalent bond formation.

FCN lewis structure formal charge :

Formal charge is a way of assigning charge on each constituent atom that briefs about the complete charge acquired by the molecule.

Mathematically, it can be represented as :

Formal charge = (Number of valence electrons in a free atom of the element) – (Number of unshared electrons on the atom) – (Number of bonds to the atom)

In addition, Charge on the molecule= sum of all the formal charges.

Formal charge of F = 7 – 6 – 1 = 0

Formal charge of C = 4 – 0 – 4 = 0         

Formal charge of N = 5 – 2 – 3 = 0

FCN lewis structure formal charge

FCN lewis structure octet rule :

Octet rule is the general rule followed by a chemist to construct a lewis dot structure which states that each atom tries to accommodate 8 electrons in its valence shell to acquire a noble gas configuration for maximum stability.

FCN lewis structure follows octet rule where every constituent atom has 8 electrons in its valence shell.

F has 8 electrons around itself including the bond pairs, C has 8 electrons including the single and triple bonds and N has 8 electrons around itself including the triple bond and the lone pairs of electrons.

Also, it is to be noted that both the bond and lone pairs of electrons are to be counted while calculating the octet electrons.

FCN solubility :

FCN lewis structure is more soluble in solvents bearing less dielectric constants. Few are the solvents mentioned below for reference :

FCN solubility in different solvents.

Is FCN linear ?

FCN lewis structure is a linear molecule. This is in accord with the VSEPR theory.

Linear shape is adopted by a triatomic molecule to have maximum distance between the lone pairs or the bond pairs and minimum repulsion between them thus giving maximum geometrical stability.

Is FCN tetrahedral ?

No, FCN lewis structure is not a tetrahedral molecule. The basic understanding of a tetrahedral molecule involves 4 atoms in tetrahedral arrangement.

Is FCN ionic ?

FCN lewis structure is ionic in nature. This is because it involves charge separation as observed in one of the resonance structures.

FCN molecule involves 3 different atoms ( F, C, N ) with a wide electronegativity difference, also involving a triple bond that has pi electron cloud.

As a result, electrons can be delocalized resulting in partial charge separation that can form dipoles between the ends of the molecule.

But it is to be noted that all the 3 atoms are non-metals so it has some covalent character as indicated by Fajan’s rule.

Is FCN polar or non polar ?

FCN lewis structure can be identified as a non-polar molecule if we consider it to be a perfectly symmetrical molecule. However, FCN with F and N at its ends are not identical which differs in their electronegativity difference.

Hence, some amount of polarity is present in the molecule as the magnitude of the dipole moment will not be similar across the ends.

It has ample amount of polarity but not sufficient enough to be called a perfectly polar molecule.

FCN dipole moments represented by the arrows.

Is FCN paramagnetic or diamagnetic ?

FCN lewis structure is paramagnetic in nature due to the presence of unpaired electrons in the p subshells of N atom. They remain in their triply excited state.

They are attracted by magnetic field. The unpaired electrons that stays as lone pair of electrons on nitrogen do not pair up but stay as unpaired electron in different subshells.

FCN lewis structure angle :

Bond angle is defined as the angle between the central atom and the bonded atoms. Here, in FCN lewis structure, the bond angle is among the three atoms i.e., F-C-N .

Since, C has sp hybridization with N atom and sp3 hybridisation with F atom, the bond angle is not exactly close to 1800 but close to it.

Is FCN a reducing agent ?

FCN lewis structure is a strong reducing agent. The anion, fluoride ion, is a strong reducing agent in a redox couple reactions.

They are called as reductant.

Is FCN a oxidizing agent ?

 FCN lewis structure is not an oxidizing agent. They are called as reductant and not an oxidant.

Is FCN symmetrical or an asymmetrical ?

FCN lewis structure is a symmetrical molecule. This is because it is a linear triatomic molecule with infinite sigma planes that is identical to the molecular plane that contains all the atoms in a plane.

Since it possesses infinite molecular planes, Coo axes , hence, it is a symmetrical molecule.

Note : Molecular plane is the plane that contains all the atoms along with the internuclear axis.

Uses of FCN :

  • It can be used as a sensitizer, insecticides, manufacturing of dyes, polymers.
  • Since it condenses to polymeric forms in room temperature, it has been used as a symmetrical network of polymers.
  • It is used as a fluorinating and nitrilating agent.

Conclusion :

FCN lewis structure is a hot topic due to its polymerisation tendency in today’s research, which through the following article, it is learnt that it is a linear triatomic molecule used for industrial purpose with a very pungent and toxic smell.

Nandita Biswas

Hello. I am doing my Masters in Chemistry with specialisation in organic and physical chemistry. Also, I have done two projects in chemistry- One dealing with colorimetric estimation and determination of ions in solutions. Other in Solvatochromism study of fluorophores and their uses in the field of chemistry alongside their stacking properties on emission. I have also specialised in Resin chemicals.

Recent Posts