Sulfur tetrachloride (SCl4) lewis structure, molecular geometry, polar or nonpolar, hybridization

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scl4 lewis structure molecular geometry

Sulfur tetrachloride appears as a white powder that has a molar mass of 173.87 g/mol. It has a chemical formula of SCl4. 

In this article, we will discuss Sulfur tetrachloride (SCl4) lewis structure, molecular geometry, polar or nonpolar, its hybridization, etc.

Sulfur tetrachloride is an unstable pale yellow solid that is easily soluble in water. Its boiling point is −20 °C and its melting point is −31 °C.

Name of MoleculeSulfur tetrachloride
Chemical formulaSCl4
Molecular geometry of SCl4See-Saw
Electron geometry of SCl4Trigonal bipyramidal
HybridizationSp3d
NaturePolar molecule
Total Valence electron for SCl434

How to draw lewis structure of SCl4?

SCl4 Lewis structure is made up of one sulfur, and four chlorine atoms, the sulfur is in the central position and chlorine atoms are in the surrounding position. The lewis structure of SCl4 contains 26 nonbonding electrons and 8 bonding electrons.

Here let’s see how to draw the lewis structure of SCl4 with ease.

Follow some steps for drawing the Lewis structure for SCl4

1. Count total valence electron in SCl4

In the very first step, we have to count the number of valence electrons available for drawing the lewis structure of SCl4. For this, we have to count the valence electrons in sulfur and chlorine atoms.

The best way to determine the valence electron in an atom is by looking at the group number in the periodic table.

As sulfur atom belongs to group 16th in the periodic table and chlorine is situated in 17th group, hence, the valence electron for sulfur is 6 and for chlorine atom, it is 7.

⇒ Total number of the valence electrons in sulfur = 6

⇒ Total number of the valence electrons in chlorine = 7

∴ Total number of valence electrons available for the SCl4 Lewis structure = 6 + 7(4) = 34 valence electrons         [∴ SCl4 molecule has one sulfur and four chlorine atoms]

valence electron in scl4 lewis structure

2. Find the least electronegative atom and place it at center

An atom with a less electronegative value is more preferable for the central position in the lewis diagram because they are more prone to share the electrons with surrounding atoms.

So, in the SCl4 molecule, the electronegativity of sulfur is 2.58 and the electronegativity of chlorine is 3.16. Clearly, sulfur is a less electronegative atom.

So, just put the sulfur in the center position and all chlorine atoms at the surrounding position.

central atom in scl4 lewis structure

3. Connect outer atoms to central atom with a single bond

In the third step, draw a single bond to connect all outer atoms (chlorine) to the central atom(sulfur).

skeletal structure of scl4

After connecting each outer atom to the central atom. Now count the valence used in the above structure.

A single bond contains two electrons, and, in the above structure, four single bonds are used, hence, (4 × 2) = 8 valence electrons are used in the above structure from the total of 34 valence electrons that is available for drawing the lewis structure of SCl4.

∴ (34 – 8) = 26 valence electrons

So, we are left with 26 valence electrons more.

4. Place remaining electrons on outer atoms and complete their octet

In this step, we have to complete the octet of outer atoms first, the octet means having 8 electrons in the valence shell of an atom.

Now in the SCl4 molecule, chlorine is the outer atom and it needs 8 electrons in its valence shell to complete its octet.

So, just start putting the remaining valence electron on chlorine atoms till they complete their octet.

placing remaining valence electron in scl4

So, all chlorine atoms in the above structure completed their octet, because all of them have 8 electrons(6 electrons represented as dots + 2 electrons in a single bond) in their valence shell. 

Now again count the total valence electrons used in the above structure.

In the above structure, there are 24 electrons represented as dots + 4 single bonds means 8 electrons are used.

Hence, (24 + 8) = 32 total electrons are used in the above structure from a total of available 34 valence electrons.

Therefore, we are left with 2 more valence electrons.

5. Complete the central atom octet and make multiple bonds if necessary

As we already completed the octet of chlorine atoms, now we have to complete the octet of the central atom which is sulfur in the SCl4 molecule.

If you look at the 4th step structure, the sulfur central atom is attached with 4 single bonds, which means, it has already 8 valence electrons in its valence shell. But we have 2 remaining valence electrons that are needed to put somewhere in the lewis diagram.

For this type of problem, a concept comes which is called expanded octet that means an atom can have more than 8 valence electrons.

Sulfur having valence electrons in the 3rd energy level, will also have access to the 3d sublevel, thus allowing for more than 8 electrons.

“Sulfur, phosphorus, silicon, and chlorine are common examples of elements that form an expanded octet.”

Hence, Sulfur central can adopt an extra valence electron due to having an expanded octet ability. So, just put the 2 remaining valence electrons on the Sulfur atom.

SCl4 lewis structure

So, we used all the valence electrons that are available for drawing the SCl4 lewis structure.

Now just check the stability of the above structure with a formal charge concept.

6. Check the stability with the help of a formal charge concept

The lesser the formal charge on atoms, the better is the stability of the lewis diagram.

To calculate the formal charge on an atom. Use the formula given below-

⇒ Formal charge = (valence electrons – Nonbonding electrons –  1/2 bonding electrons)

Let’s count the formal charge on the chlorine atom first, all chlorine atoms in the SCl4 Lewis structure(5th step) have the same bonded pair and lone pair, so, just count the F.C. for the one chlorine atom.

For chlorine atom:

⇒ Valence electrons of chlorine = 7

⇒ Nonbonding electrons on chlorine= 6

⇒ Bonding electrons around chlorine(1 single bond) = 2

∴ (7 – 6 – 2/2) = 0 formal charge on all chlorine atoms.

 For sulfur atom

⇒ Valence electrons of sulfur = 6

⇒ Nonbonding electrons on sulfur = 2

⇒ Bonding electrons around sulfur (4 single bonds) = 8

∴ (6 – 2 – 8/2) = 0 formal charge on the sulfur central atom.

formal charge in scl4 lewis structure

So, this is our most stable and appropriate lewis structure of SCl4 (Sulfur tetrachloride).

What are the electron and molecular geometry of SCl4?

The molecular geometry of SCl4 is See-Saw because the central atom sulfur is attached with four bond pairs and there is one lone pair on it, so, according to the VSEPR theory, these bond pairs and lone pair around the sulfur will repel each other, as a result, they will be pushed apart giving the shape of SCl4 similar to the See-Saw.

A molecule has a see-saw structure when the central atom is bonded to 4 other atoms and has 1 lone pair.

The electron geometry for SCl4 is trigonal bipyramidal since the central atom Sulfur has five regions of electron density(4 bond pairs + 1 lone pair).

Electron geometry and molecular geometry of SCl4

Hybridization of SCl4

Let’s find the hybridization of SCl4 through the steric number of its central atom.

“Steric number is the addition of a total number of bonded atoms around a central atom and the lone pair present on it.”

∴ Steric number of SCl4 = (Number of bonded atoms attached to sulfur + Lone pair on sulfur)

As per the lewis structure of SCl4, the sulfur atom is bonded with four chlorine atoms and it contains one lone pair also.

∴ Steric number of SCl4 = (4 + 1) = 5

Steric numberHybridization
1S
2Sp
3Sp²
4Sp³
5Sp³d
6Sp³d²

So, for a steric number of five, we get the Sp3d hybridization for the SCl4 molecule.

Sulfur tetrachloride polarity: is SCl4 polar or nonpolar?

Is SCl4 polar or non-polar? SCl4 is a polar molecule because of its asymmetrical structure which causes uneven distribution of charges in the molecule, thus, dipole moments generated along with the bonds are unable to cancel out each other, making SCl4 a polar molecule in nature.

Also, in the SCl4 molecule, chlorine is more electronegative than sulfur, so, the electronegativity difference between these atoms makes the bond polar(S-Cl).

⇒ The electronegativity of chlorine = 3.16

⇒ The electronegativity of sulfur = 2.58

∴ The difference of electronegativity between sulfur and chlorine = 0.58

Since chlorine is a little more electronegative than the sulfur atom and molecular geometry of SCl4 is also asymmetrical, thus, the overall charge distribution of a molecule is uneven resulting in some dipole moment which makes SCl4 polar in nature.

FAQ

How many bonding pairs and lone pairs are present around the central atom in the lewis structure of SCl4?

Bonding pairs are the pair of electrons that are in a bond. A single bond has one bond pair means 2 bonding electrons. 

Lone pairs are those represented as dots in the lewis diagram that do not take part in the formation of bonds and are also called nonbonding electrons.

By looking at the SCl4 lewis structure, we see that sulfur is the central atom that is attached with 4 bond pairs and it contains 1 lone pair also.

Why the Sulfur atom in the SCl4 lewis structure contains more than 8 electrons and violate the octet rule?

It is usually seen that the atom completes its octet when it has 8 electrons in its valence shell. But Sulfur central atom in the SCl4 lewis structure has 10 electrons(8 bonding electrons represent by single bonds + 2 nonbonding electrons represent by dots).

So, here, Sulfur violates the octet as it contains more than 8 electrons. This is because it has the ability to expand the octet.

“Sulfur having valence electrons in the 3rd energy level will also have access to the 3d sublevel, thus allowing for more than 8 electrons.”

 

Preparation and Reactions of Sulfur tetrachloride

Sulfur tetrachloride is directly prepared by reacting sulfur dichloride with chlorine at 193 K.

⇒ SCl2 + Cl2 → SCl4

When sulfur tetrachloride exposes above 242 K, it starts to decompose to sulfur dichloride and chlorine.

⇒ SCl4 → SCl2 + Cl2

Sulfur tetrachloride is soluble in water, hence, it hydrolyzes readily to form sulfur dioxide and hydrogen chloride.

⇒ SCl4 + 2H2O → SO2 + 4HCl

When sulfur tetrachloride is treated with the 2 moles of nitric acid and with some water, it forms sulfuric acid, hydrogen chloride, and nitrogen dioxide.

⇒ SCl4 + 2HNO3 + 2H2O → H2SO4 + 2NO2 + 4HCl

Summary

  • The total valence electron is available for drawing the SCl4 lewis structure is 34.
  • The steric number of the sulfur central atom in the SCl4 molecule is 5, thus, it forms Sp3d hybridization.
  • SCl4 is a polar molecule because of asymmetrical geometry that causes the non-uniform distribution of charge in the molecule.
  • In the SCl4 lewis structure, a total of 13 lone pairs and 4 bond pairs are present.
  • The molecular geometry of SCl4 is see-saw and its electron geometry is trigonal bipyramidal.
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