The CN- is the chemical formula of cyanide. It comes under the functional group cyano which is a pseudohalide anion.
Cyanide compound contains carbon and nitrogen and has various forms like sodium cyanide, potassium cyanide, hydrogen cyanide, etc. It is a colourless gas and released by various ways like plant decay products, various microorganisms like bacteria, algae, fungi, etc. In contact with acids it becomes most dangerous. In this editorial we are learning about CN- lewis structure and its detailed facts.
How to draw lewis structure for CN-?
The points while drawing lewis structure to be noted as:
- Calculation of total valence electrons present on structure.
- Select the element with lowest electronegativity for central position in structure.
- Do bonding between all the elements present in structure.
Chemical formula for cyanide is CN-.
Molecular weight of CN- is 26.02 g mol-1.
Molecular geometry of CN- is linear in shape.
CN- has sp hybridization.
CN- is polar in nature.
There are two elements involves in the formation of CN- lewis structure i.e. nitrogen (N) and carbon (C) which is connected by triple bonds. In CN- lewis structure, it has two lone electron pairs one each on carbon and nitrogen atoms.
- Total valence electrons of CN-.molecule calculation
Let us first calculate the total valence electrons available on CN- molecule. As per the periodic table, carbon atom comes under 14th group of periodic table and nitrogen atom comes under 15th group of periodic table. So, both carbon and nitrogen atoms have 4 and 5 valence electrons respectively.
While calculating valence electrons on CN- lewis structure, we have to add 1 for minus (-) charge on CN- ion.
Therefore, Carbon atoms valence electrons = 4
Nitrogen atoms valence electrons = 5
Total CN- valence electrons = 4 (C) + 5 (N) + 1 (-) = 10
Hence, CN- lewis structure has ten valence electrons total.
- Element with lowest electronegativity for central position
In CN- lewis structure we don’t have to find the elements with lowest electronegativity. As CN- molecule involves only two elements carbon and nitrogen. So, there is no need of central position in compounds containing only two elements. We can place them besides each other.
- Bonding between all elements
In this step we have to create bonding between all the elements present in the structure. So, in CN- molecule we have to just make a single bond within carbon and nitrogen to connect them with each other.
Therefore, we engaged two electrons out of ten valence electrons of CN- ions in bonding the elements. As the two electrons becomes bond pair electron out of ten electrons, so now only eight electrons get remains for distribution in CN- lewis structure.
CN- lewis structure octet rule
To follow the octet rule we have to distribute all the remaining valence electrons within carbon and nitrogen atoms of CN- lewis structure. Fill the electrons first on the most electronegative atom of the CN- lewis structure. Here, N is more electronegative in nature than C, so start putting electrons on nitrogen atom first.
Nitrogen atom already has two electrons in a single bond pair with C atom it needs more six electrons to fill its octet. So after filling six electrons on N atom there are only two electrons get remain for further sharing with carbon atom.
So, the remaining two electrons get placed on carbon atom, we will get the following structure after putting all the eight electrons on CN- lewis structure.
In the above structure N seems satisfied as it has eight electrons in its outer shell i.e. complete octet but carbon atom is not satisfied as it has only four electrons. So, we have to satisfy both the C and N atoms by equal distribution of electrons to complete its octet.
So, for that we have to make more covalent bonds between C and N atoms to fulfil its octet. As the carbon atom has less electrons so we have to transform lone electron pairs of nitrogen into bond pairs to get covalent bonds. Now, we get the following structure.
So, in the above structure two lone electron pairs of nitrogen get converted into two bond pairs to complete the octet of carbon. Now both the carbon and nitrogen atoms of CN- lewsi structure have complete octets.
CN- lewis structure formal charges
If the atoms have little formal charges in any lewis structure then the there is more stability in lewis structure. The calculative formula for formal charge calculation of any atoms in lewis diagram is as follows:
Formal charge = (valence electrons – non-bonding electrons – ½ bonding electrons)
Let us calculate the formal charges on CN- lewis structure. So first just we have to calculate the carbon atom formal charge.
Carbon atom: Valence electrons on Carbon = 04
Non-bonding electrons on Carbon = 02
Bonding electrons with Carbon =06
Formal charge on carbon = (4 – 2 – 6/2) = -1
Thus, there is -1 formal charge on carbon atom.
Nitrogen atom:Valence electron on nitrogen atom = 05
Non-bonding electron pair on nitrogen atom = 02
Bonding electrons on nitrogen atom =06
Formal charge on nitrogen = (05 – 02 – 6/2) = 0
Hence, the nitrogen atom of CN- lewis structure has zero formal charge.
So, this concludes that CN- lewis structure has -1 formal charge on it.
CN- lewis structure lone pairs
In CN- lewis structure, there are total two lone electron pairs are present i.e. one on carbon atom and one on nitrogen after the complete distribution of valence electrons in CN- molecule.
Hence, the total two lone electron pairs are present on CN- lewis structure.
CN- lewis structure shape
To determine the shape of any lewis structure we have to follow the notations of VSEPR theory when there are more than two elements present in any molecular diagram. Here, in CN- lewis structure there are only two essential elements are present i.e. carbon and nitrogen. The generic formula for CN- lewis structure is AXE.
According to geometry of ions in VSEPR theory the CN- ion comes under linear shape. In CN- lewis structure, there is a symmetrical valence electrons distribution on both carbon and nitrogen atoms to form an anion. CN- molecule also has same lone electron pairs. Therefore to maintain the stability of structure and to decrease the repulsion between atoms the linear shape is most suitable for CN- lewis structure.
So, the CN- lewis structure is linear in shape as per VSEPR theory.
We have already discussed about CN- molecules electronegativities, formal charges and its molecular geometry and shape. Now we are discussing about the hybridization of CN- ions.
If we see the CN- lewis structure, the formation of a triple bond has been seen to us within carbon atom and nitrogen atom, which indicates the presence of one sigma (σ) bond and two pi (π) bonds in CN- structure. The pi bond is not involved in the hybridisation of CN- structure as its formation is done by p orbitals side-to-side overlap. Sigma (σ) bond has the end-to-end overlap of 2 orbitals.
The hybridisation of any structure is based on its steric number. Hybridization of CN- lewsi structure is based on the steric number of both carbon atom and nitrogen atom.
The addition of total number of bonded elements associated with central atom and its lone electron pairs is the steric number.
Steric number of CN- = (no. of bonded elements or atoms attached central element + central atom having lone pair of electrons)
As there is no central atom in CN- structure and presence of only one sigma bond and one lone electron pair for both elements of CN- molecule i.e. C and N.
So, the Steric number for CN- = 1 (σ) + 1 (lone pair electron of c and N)
CN- lewis structure resonance
CN- lewis structure can show two possible resonance structures. We already know that CN- molecule have ten valence electrons i.e. four electrons from C, five electrons from N and extra one electron for negative charge of CN-. So, the two possible resonance structure of CN- ion may be as shown below.
The left hand side resonance structure has a triple bond between C and N and also has a lone electron pair on each both atoms. There is a zero formal charge on N and -1 formal charge on C, as N requires 5 electrons and which it gets total 5 from two lone electron pair and three bond pairs. Similarly C requires 4 electrons, but it also gets total 5 i.e. two from lone electron pair and one from each three bond pairs.
The right hand side resonance structure shows a double bond within C and N with two lone electron pairs on N and one lone electron pair on C. In this structure N atom has -1 formal charge as it has total six electrons i.e. two from bond pairs and four from lone electron pairs.
If we compare both the resonance structures, the first left hand side structure contribute more to the resonance rather than it has a negative charge on the C atom which is less electronegative than N. This negative occurs due to the formation of triple bond within C and N atoms which is its great factor for stability.
But as per the resonance structure rule, the maximum covalent bonds should be there in a stable resonance structure with the full octet of all elements present.
Thus the structure on left hand side is more stable in nature than right hand side structure as it has more covalent bonds.
CN- polar or nonpolar
Now, let us discuss the polar/ non-polar nature of CN- structure. If we see the electronegativity difference of C and N atom, the C atom has electronegativity 2.55 and nitrogen atom has electronegativity 3.04, so the difference of electronegativities is 0.49.
So according to Paulings rule, if the electronegativity difference between 0.4 to 1.7 then the bond comes under polar nature. Even the C atom bears a partial positive charge on it and becomes slightly more electropositive compare to nitrogen as nitrogen has partial negative charge on it.
The triple bond of CN- ion slightly act as polar bond and CN- molecules ionic nature gives it the capacity to interact with other polar solvents like H2O, etc. So, CN- lewis structure shows polar nature.
CN- lewis structure bond angle
CN- lewis structure has equal distribution of valence electrons and lone pair electrons on both carbon and nitrogen atom to form stable. Also the molecular geometry and shape of CN- lewis structure is linear.
So, the bond angle of CN- lewis structure is 180 degree.
- Cyanide is used in paper industry.
- Cyanide is used in textiles industry.
- Cyanide is used in making plastics.
- Cyanide is used in photograph developing chemicals.
- In metallurgy, cyanide salts are used as metal cleanser, for electroplating, etc.
- Cyanide is also used to remove gold from its ore.
- Cyanide gas is used to eliminate insects and pests from buildings, houses and ships.
- Zyklob B which is the form of hydrogen cyanide was used by Germany in WW-II as a genocidal agent.
- Hydrogen cyanide gas with some other chemicals was used in Iran – Iraq war in 1980’s
- Some cyanide is used in industries of jewellery making and food additives.
- Cyanide cannot use as a common chemical as it is very dangerous to human body to inhale.