Hydrogen sulfide (H2S) Molecular geometry, electron geometry, Bond angle, hybridization
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Hydrogen sulfide is a colorless gas with a molar mass of 34.08 g·mol−1. It is poisonous and flammable with a smell like rotten gas. It is also dangerous for the environment.
In this article, we will discuss the following things- Hydrogen sulfide (H2S) molecular geometry, electron geometry, lewis structure, its bond angle, polarity, hybridization, etc.
Name of Molecule
Hydrogen sulfide (H2S)
Bond angle
92.1º
Molecular geometry of H2S
Bent or V-shaped
Electron geometry H2S
Tetrahedral
Hybridization
Nil (No hybridization)
Total Valence electron for H2S
8
The formal charge of H2S
0
Hydrogen sulfide is produced by anaerobic digestion in which microorganisms break down the organic matter in the absence of oxygen. It also occurs in volcanic gases and in well water also. It can also be obtained by its separation from sour gas.
How to draw H2S/SH2 lewis structure and find it's hybridization?
H2S Lewis structure contains two hydrogens and one sulfur atom. Sulfur is the central atom and contains 2 lone pairs whereas both hydrogen is connected to the central atom with the help of a single bond.
Lewis’s structure of SH2 is really helpful to determine its electron geometry, molecular shape, number of shared pair, and lone pair electrons.
Follow these steps to draw the lewis dot structure for H2S
Step 1:In the first step, determine the total valence electron present in H2S. As we know hydrogen only has one valence electron in its last shell and Sulfur belongs to the 16th group in the periodic table so it contains 6 electrons in its last shell.
∴ Total valence electron available for drawing the H2S lewis structure = 1×2 + 6 = 8 valence electron
Step 2:Find the central atom for drawing the lewis dot structure for H2S. To determine the central atom in the H2S molecule you have two ways.
Find the central atom by finding the least electronegative atom in the H2S molecule. Clearly, sulfur has less electronegativity compared to hydrogen because hydrogen has a higher tendency to attract electrons, also, hydrogen only needs two-electron to fulfill its valence shell.
Place the atom at the center which has a greater valence. Clearly, Sulfur has a valence power of 6 and Hydrogen has only 1. So, Sulfur must be paced at the center in the lewis diagram.
Step 3:Now construct the structure of H2S by connecting the single bond to the central atom.
Step 4:After placing the central atom and connecting with it a single bond, we have to fulfill the octet rule for every atom in H2S to maintain the last requirement of the lewis diagram.
A hydrogen atom needs only two electrons to fulfill its octet and the sulfur atom needs eight electrons to fulfill the octet.
The hydrogen outer shell is already full because it shares two electrons already with the help of a single bond. So, no need to place electrons around hydrogen.
Now for Sulfur, we need 8 electrons but only 4 electrons are shared with the help of two single bonds. So, we have to place 4 more electrons around sulfur to complete its octet rule and fulfilling the criteria for drawing the lewis dot structure for SH2.
Lewis structure for SH2 or H2S
Step 5: Now in the final step, minimize the charges on the atom of H2S by converting lone pairs to covalent bonds.
But there is no charge on the atom(the formal charge on hydrogen and sulfur is zero), so, no need to make any covalent bond.
This lewis structure is also called Dihydrogen sulfide lewis structure or dihydrogen monosulfide lewis structure.
It might surprise you, that, H2S will not form any hybridization. This can be explained by using Drago’s rule.
The molecule that comes under Drago’s rule has no hybridization and has the least bond angle.
According to Drago’s rule, the molecule will form “no hybridization” in some conditions. The conditions are-
The central atom is placed in 3rd period or below the 3rd period.
At least one lone pair on the central atom.
The electronegativity of the terminal atom is less than approx 2.5.
So, in the case of H2S, the central atom i.e sulfur is in the 3rd period, it has 2 lone pairs. Also, the electronegativity of terminal atoms (hydrogen) is 2.1 which is less than 2.5.
Therefore, according to Drago’s rule, H2S has no hybridization.
One more explanation why H2S has no hybridization –
Drago rule says that no hybridization takes place if the energy difference between the atomic orbitals of the atoms is too high.
“There is no hybridization in H2S .The hybridization concept says that only the orbitals with same orientation and less energy difference can combine to form hybridized orbitals.
As vacant orbital of S have quite higher energy compared to 1s orbital of H atom. Hence, these elements don’t form hybrid orbitals.”
Therefore, H2S has no hybridization.
Some Example-in H2S, H2Se, H2Te, PH3, AsH3, SbH3, etc no hybridization takes place according to Drago’s rule.
What are the electron and molecular geometry of H2S?
The molecular geometry of H2S is bent. This is because the two lone pair electrons on sulfur central atom repel each other as well as adjacent bonded pair electrons, as a result, these electron pair(lone pair and bond pair) takes the position where the repulsion becomes minimum and they attains the stability(no further repulsion force exist in electrons pairs).
Hence, the final shape or molecular geometry of H2S appears like a bent structure or V-shaped.
According to the VSEPR theory, to reduce the repulsion. the electron pairs move to maximum angle apart from each other and become stable.
Also, electron geometry for H2S is tetrahedral because 4 electrons which make 2 lone pairs around a sulfur atom are arranged in a tetrahedral geometry.
H2S molecular geometry or shape
To determine the electron and molecular geometry of H2S, its lewis structure, and VSEPR theory play an important role.
Electron geometry considers all electrons as well lone pairs to determine the geometry of H2S whereas Molecular geometry only considers bonded atoms of the molecules to determine the shape of H2S.
Another way to find electron/molecular geometry of H2S
AXN method is very useful to determine electron geometry or molecular shape for H2S. But you have to make a lewis structure of H2S for using this method.
AXN method–
A represents the central atom.
X represents the bonded pair of electrons.
N represents the lone pair of electrons.
As per H2S lewis structure –
Sulfur is the central atom.
2 bonded pairs of electrons are attached to the central atom sulfur.
2 lone pairs on the sulfur central atom.
Therefore, the generic formula of hydrogen sulfide is AX2N2 for finding the molecular or electron geometry of H2S.
So, AX2N2 gives the molecular geometry of H2S is bent and the electron geometry is tetrahedral according to VSEPR Shape Chart.
Well, we know the polar molecule has some dipole moment because of unequal distribution of charges whereas the non-polar molecule has an equal distribution of charges that cause zero dipole moment because they cancel out each other due to the symmetrical shape of the molecule.
The polarity of H2S is dependent upon its molecular shape, electronegativity, and dipole moment.
H2S molecule has non-polar bonds because the electronegativity of bonds(H-S) is lesser than 0.5, as Hydrogen electronegativity is 2.20 and sulfur electronegativity is 2.58 and their difference is 0.38.
According to the Pauling scale, if the difference of an atom’s electronegativity is less than 0.5, the bond is considered nonpolar.
But overall H2S molecule is slightly polar because it is non-linear and it has bent molecular geometry and the central atom (S) is more electronegative than (H), therefore, the negative charge develops on the S atom and positive charge on the H atom.
This will induce some net dipole moment in H2S which makes it a slightly polar molecule.
In the mathematical term, dipole moment can be expressed as-
⇒ product of charges of two atoms and the distance between them
∴ D = Q * R
⇒ D denotes dipole moment
⇒ Q denotes charge on atoms
⇒ R denotes the distance between atoms
Uses of Hydrogen Sulfide
It is used to produce sulfur and sulfuric acid.
It is used to produce pesticides, leather, and pharmaceuticals.
It is also used in nuclear power plants for the production of heavy water.
H2S is used in chemical analysis.
It can also be used in agriculture as a disinfectant.
Properties of Hydrogen Sulfide
H2S is slightly denser than air.
The hydrogen sulfide chemical formula is H2S or SH2.
It has a molar mass of 34.08 g·mol−1
H2S has a boiling point of −60 °C and a melting point of −82 °C.
It has a pungent smell, like rotten eggs.
It has a vapor pressure of 1740 kPa.
H2S magnetic susceptibility is −25.5·10−6 cm3/mol.
Hydrogen sulfide act as a reducing agent.
Its refractive index is 1.000644
Hydrogen sulfide can be produced by when ferrous sulfide is treated with a strong acid like HCl in standard lab preparation.
⇒ FeS + 2 HCl → FeCl2 + H2S
Most metals and non-metals sulfides after exposure to water liberate Hydrogen sulfide.
⇒ 6 H2O + Al2S3 → 3 H2S + 2 Al(OH)3
H2S has many names like- Dihydrogen monosulfide, sewer gas, dihydrogen sulfide, sour gas, sulfane, sulfur hydride, etc.
FAQ
Why is the bond angle in H2O greater than H2S?
This is because oxygen is more electronegative than the sulfur atom, hence, it will attract more electrons towards itself that cause more bond pair-bond pair repulsion between the bonds, and this finally causes the widening of bond angle in H2O.
∴ The bond angle of H2O = 104.5°
∴ The bond angle of H2S = 92.1°
Why the molecular geometry of H2S is bent whereas its electron geometry is tetrahedral?
As we already discussed, “electron geometry is determined with the help of both lone electron pairs and bonds pair in a molecule whereas molecular geometry determined using only the bonds present in the molecule”.
According to the H2S lewis structure, the central atom has 2 lone pairs and 2 bonded pairs, hence, according to the VSEPR theory, H2S has 4 regions of density(2 lone pairs + 2bond pairs) around the central atom(sulfur).
∴ Four regions of electron density always form a tetrahedral geometry, hence, the electron geometry of H2S is tetrahedral.
While calculating the molecular shape, we will not consider the lone pair as “the molecular shape has to do with the shape of the actual molecule, not the electrons, so they are not accounted for in that sense”.
But we can’t neglect the effect of lone pair on a bond angle while calculating the molecular shape of the molecule.
As there are two lone pairs present on the sulfur central atom in the H2S molecule, hence, it will contract the bond pair, and this makes its shape appears like a bent structure.
Therefore, the molecular geometry or shape of H2S is bent while its electron geometry is tetrahedral.
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