Lewis structure of SCN-

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The Lewis structure of SCN^– contains two double bonds, with carbon in the center, and sulfur and nitrogen on either side. There are two lone pairs on the sulfur atom and nitrogen atom, and the carbon atom does not have any lone pair.

Plus, there is a negative (-1) charge on the nitrogen atom.

Steps

By using the following steps, you can easily draw the Lewis structure of SCN^–:

#1 Draw skeleton
#2 Show chemical bond
#3 Mark lone pairs
#4 Complete octet on central atom
#5 Calculate formal charge and check stability

Let’s one by one discuss each step in detail.

#1 Draw skeleton

In this step, first calculate the total number of valence electrons. And then, decide the central atom.

• Let’s calculate the total number of valence electrons

We know that… sulfur is a group 16 element, carbon is a group 14 element, and nitrogen is a group 15 element. Hence, sulfur has six valence electrons, carbon has four valence electrons, and nitrogen has five valence electrons.

Now SCN^– has one sulfur atom, one carbon atom, and one nitrogen atom.

So the total number of valence electrons = valence electrons of sulfur atom + valence electrons of carbon atom + valence electrons of nitrogen atom

And SCN^– has a negative (-1) charge, so we have to add one more electron.

Therefore, the total number of valence electrons = 6 + 4 + 5 + 1 = 16

• Now decide the central atom

The atom with the least electronegative value is placed at the center. By looking at the periodic table, we get the electronegativity values for sulfur, carbon, and nitrogen as follows:

Electronegativity value of sulfur = 2.58
Electronegativity value of carbon = 2.55
Electronegativity value of nitrogen = 3.04

Obviously, carbon is less electronegative than sulfur and nitrogen. Hence, assume that carbon is the central atom.

So now, put carbon in the center and sulfur and nitrogen on either side. And draw the rough skeleton structure for the Lewis structure of SCN^– something like this:

Also read: How to draw Lewis structure of HNO₃ (5 steps)

#2 Show chemical bond

Place two electrons between the atoms to show a chemical bond. Since carbon is surrounded by sulfur and nitrogen, use four electrons to show two chemical bonds as follows:

#3 Mark lone pairs

As calculated earlier, we have a total of 16 valence electrons. And in the above structure, we have already used four valence electrons. Hence, twelve valence electrons are remaining.

Two valence electrons represent one lone pair. So twelve valence electrons = six lone pairs.

Note that chlorine is period 3 element, so it can keep more than 8 electrons in its last shell. And both (carbon and nitrogen) are the period 2 elements, so they can not keep more than 8 electrons in their last shell.

Also, make sure that you start marking these lone pairs on outside atoms first. And then, on the central atom.

The outside atoms are sulfur and nitrogen, so sulfur and nitrogen will get three lone pairs. And the central atom (carbon) will not get any lone pair, because all six lone pairs are used.

So the Lewis structure of SCN^– looks something like this:

In the above structure, you can see that the octet is completed on the outside atom. But, the central atom (carbon) doesn’t form an octet.

So in the next step, we have to complete the octet on the central atom.

Also read: How to draw Lewis structure of CH₃NH₂ (4 steps)

#4 Complete octet on central atom

Remember that carbon is a period 2 element, so it can not keep more than 8 electrons in its last shell.

Now carbon already has four valence electrons. Hence, carbon needs four more valence electrons to complete its octet.

So convert one lone pair from the sulfur atom and nitrogen atom to make a new bond with the carbon atom. And then, the Lewis structure of SCN^– looks something like this:

In the above structure, you can see that the octet is completed on the central atom (carbon), and also on the outside atoms. Therefore, the octet rule is satisfied.

After completing the octet, one last thing we need to do is, calculate the formal charge and check the stability of the above structure.

Also read: How to draw Lewis structure of CH₃Cl (4 steps)

#5 Calculate formal charge and check stability

The following formula is used to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

Collect the data from the above structure and then, write it down below as follows:

• For sulfur atom

Valence electrons = 6
Nonbonding electrons = 4
Bonding electrons = 4

Formal charge = 6 – 4 – ½ (4) = 0

• For carbon atom

Valence electrons = 4
Nonbonding electrons = 0
Bonding electrons = 8

Formal charge = 4 – 0 – ½ (8) = 0

• For nitrogen atom

Valence electrons = 5
Nonbonding electrons = 4
Bonding electrons = 4

Formal charge = 5 – 4 – ½ (4) = -1

Mention the formal charges of atoms on the structure. So the Lewis structure of SCN^– looks something like this:

In the above structure, you can see that the formal charges of atoms are closer to zero. Therefore, this is the most stable Lewis structure of SCN^–.

And each horizontal line drawn in the above structure represents a pair of bonding valence electrons.

Now SCN^– is an ion having a negative (-1) charge, so draw brackets around the above Lewis structure and mention that charge on the top right corner. And then, the Lewis structure of SCN^– looks something like this:

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Related

• Lewis structure of HNO₃
• Lewis structure of CH₃NH₂
• Lewis structure of CH₃Cl
• Lewis structure of SiO₂
• Lewis structure of ethanol

External links

• SCN- lewis structure, molecular geometry, bond angle, hybridization – Topblogtenz
• Chemical Bonding: SCN- Lewis Structure – The Geoexchange
• SCN- Lewis Structure in 6 Steps (With Images) – Pediabay
• Lewis Structure and Resonance Structures of SCN – Chemistry School
• Draw the Lewis structure of SCN- and identify its geometry – Homework.Study.com
• SCN- Lewis Structure, Molecular Geometry, Hybridization and Shape – Geometry of Molecules
• SCN- Lewis Structure (Thiocyanate Ion) – Pinterest
• Write the possible Lewis structures for the thiocyanate anion SCN – Studocu
• From a consideration of the Lewis structure of the thiocyanate ion, SCN–, in which carbon has a double bond with both the sulfur and nitrogen atoms, what are the formal charges on the sulfur, carbon, and nitrogen atoms? – Socratic
• Thiocyanate Ion (SCN-) Formal Charge – Chemistry Learner
• What is the most “important” resonance structure of SCN – Chemistry Stack Exchange
• We can draw three inequivalent Lewis structures for the thiocyanate ion, SCN – Chegg
• Three inequivalent Lewis structures for the thiocyanate ion, SCN- – Numerade
• From a consideration of the lewis structure of the thiocyanate ion, scn-, in which carbon has a double bond with both the sulfur and nitrogen atoms, the formal chareges on the sulfur, carbon, and nitrogen atoms are, respectively – Brainly
• Thiocyanate, SCN- is a fun ligand. Draw the Lewis structure and all of the possible resonance structures. List all of the ways you can describe the ligand – Bartleby
• SCN- (Thiocyanate) Oxidation Number – ChemicalAid
• Thiocyanate, SCN-, has three possible structures – Course Hero
• Why is the charge of SCN- -1? If the charge of sulfide is -2, shouldn’t SCN have a charge of -3? Or is the polyatomic bonded by a covalent bond? – Quora
• Which statement about the thiocyanate ion, SCN- is true? – Chemical Forums