Hydrogen sulfide (H2S) Molecular geometry or shape, electron geometry, Bond angle, hybridization, Lewis structure, formal charges
Hydrogen sulfide (H2S), informally known as the ‘rotten egg gas’’ is a colorless gas with a distinct pungent odor that can be detected even at very low concentrations. It is commonly used for the production of sulfuric acid and also as a reducing agent in organic chemistry.
In this article, we have taught you how to draw the Lewis dot structure of H2S, what is its molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, as well as whether it is a polar or a non-polar gas.
So, what are you waiting for? Dive into the article and learn all about hydrogen sulfide (H2S).
The Lewis dot structure of hydrogen sulfide (H2S) consists of a sulfur (S) atom at the center. It is surrounded by 2 hydrogen (H) atoms, one on each side, by a single covalent bond. The central S-atom carries 2 lone pairs of electrons, while there is no lone pair on any of the terminal H-atoms.
You can easily learn to draw the Lewis structure of H2S by following the simple steps given below, one at a time.
Steps for drawing the Lewis dot structure of H2S
1. Count the total valence electrons present in H2S
The first step while drawing the Lewis structure of a molecule is to count the total valence electrons present in it. The valence electrons present in an elemental atom can be determined by identifying its position in the Periodic Table of Elements.
H2S consists of two distinct elements, i.e., hydrogen and sulfur.
Hydrogen (H) lies at the top of the Periodic Table with a single valence electron only. In contrast, sulfur (S) is present in Group VI A (or 16) of the Periodic Table, possessing 6 valence electrons.
Total number of valence electrons in hydrogen = 1
Total number of valence electrons in sulfur = 6
The H2S molecule comprises 1 S-atom and 2 H-atoms.
∴ Therefore, the total valence electrons available for drawing the Lewis dot structure of H2S = 2(1) + 1(6) = 8 valence electrons.
2. Choose the central atom
By convention, the least electronegative atom out of all those available is chosen as the central atom while drawing the Lewis structure of a molecule.
The least electronegative atom can easily form covalent bonds with other atoms by sharing its electrons.
In H2S, hydrogen (E.N = 2.20) is less electronegative than sulfur (E.N = 2.58).
However, the H-atom is an exception as it cannot be chosen as the central atom in any Lewis structure. It can accommodate a total of 2 valence electrons, forming a single covalent bond with 1 adjacent atom only.
So, in the H2S Lewis structure, we are left with no choice but to place the S-atom as the central atom while the two H-atoms occupy terminal positions, as shown below.
3. Connect the outer atom with the central atom
The central S-atom is joined to both the H-atoms using single straight lines.
Each straight line represents a single covalent bond, i.e., a bond pair containing 2 electrons.
2 H-S single bonds denote 2(2) = 4 valence electrons of H2S are consumed till this step out of the 8 initially available.
4. Complete the duplet of the outer atoms
Both the H-atoms already have a complete duplet in the H2S Lewis dot structure obtained in step 3. So, we do not need to make any changes with regard to the H-atoms in this structure.
5. Complete the octet of the central atom
Total valence electrons used till step 4 = 4 valence electrons
Total valence electrons – electrons used till step 4 = 8 – 4 = 4 valence electrons.
Hence, these 4 valence electrons are placed as 2 lone pairs on the central S-atom.
Now, the central S-atom automatically has a complete octet with 2 single covalent bonds and 2 lone pairs surrounding it.
A final step is to check the stability of this Lewis structure by applying the formal charge concept. Let’s do that in the next step.
6. Check the stability of Lewis’s structure using the formal charge concept
The less the formal charge on the atoms of a molecule, the better the stability of its Lewis structure.
The formal charges can be calculated using the formula given below.
Formal charge = [valence electrons- nonbonding electrons- ½ (bonding electrons)].
Now let us use this formula and the Lewis structure obtained in step 5 to determine the formal charges present on the H2S-bonded atoms.
For hydrogen atom
Valence electrons of hydrogen = 1
Bonding electrons = 1 single bond = 1(2) = 2 electrons
Zero formal charges present on all the bonded atoms imply that there is no overall charge present on the H2S Lewis structure.
Thus, it is the correct and most stable Lewis representation of hydrogen sulfide.
Now let us find out what is the molecular and electron geometry of H2S.
What are the electron and molecular geometry of H2S?
The molecular geometry or the shape of hydrogen sulfide (H2S) is bent, angular or V-shaped. However, its ideal electron pair geometry is tetrahedral. The presence of 2 lone pairs of electrons on the central S-atom leads to a strong repulsive effect, thus distorting the overall molecular geometry of H2S.
Molecular geometry of H2S
The molecular geometry or shape of H2S is bent, angular or V-shaped.
There are 2 lone pairs of electrons on the central S-atom in H2S, leading to strong lone pair-lone pair and lone pair-bond pair electronic repulsions. The terminal H-atoms tilt away from the central S-atom to minimize this strong repulsive effect. Thus, the H2S molecule occupies a bent or V-shape, as shown below.
Electron geometry of H2S
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, the ideal electron geometry of a molecule containing a total of 4 electron density regions around the central atom is tetrahedral.
In H2S, 2 single bonds and 2 lone pairs surround the central sulfur atom, making a total of 4 electron density regions. Hence, its electron geometry is tetrahedral.
An easy trick to finding a molecule’s electron and molecular geometry is using the AXN method.
AXN is a simple formula representing the number of bonded atoms and lone pairs on the central atom.
It is used to predict the shape and geometry of a molecule using the VSEPR concept.
AXN notation for H2S molecule
A in the AXN formula represents the central atom. In the H2S molecule, a sulfur (S) atom is present at the center, so A = S.
X denotes the atoms bonded to the central atom. In H2S, two H-atoms are single-covalently bonded to the central S-atom. So X = 2 for H2S.
N stands for the lone pairs present on the central atom. As per the Lewis structure of H2S, the central S-atom carries 2 lone pairs of electrons. Thus, N = 2 for H2S.
As a result, the AXN generic formula for H2S is AX2N2.
Now, you may have a look at the VSEPR chart below.
The VSEPR chart confirms that the molecular geometry or shape of a molecule with an AX2N2 generic formula is bent, angular or V-shaped, while its electron geometry is tetrahedral, as we already noted down for hydrogen sulfide (H2S).
Hybridization and bond angle of H2S
The hybridization of H2S is an exception. It might surprise you, but the hydrogen sulfide (H2S) molecule indeed has nil or no hybridization, as perDrago’s rule.
Drago’s rule states that we don’t need to consider the hybridization of a molecule if:
The central atom is placed in 3rd period or below the 3rd period.
At least one lone pair is present on the central atom.
The electronegativity of the terminal atom is less than approx. 2.5.
In H2S, the central atom (S) is present in Period 3; it has 2 lone pairs of electrons and the H-atoms bonded to it have electronegativity values less than 2.5. It is said that a high energy difference exists between the 3s and 3p orbitals of sulfur, so it is difficult for them to hybridize.
Therefore, chemical bonding in H2S cannot be satisfactorily explained by the hybridization concept nor by the VSEPR theory. Rather, it more aptly follows the simple valence bond theory (VBT) of chemical bonding, which says that the overlapping of incompletely filled atomic orbitals leads to the formation of a new chemical bond.
It is because of this reason that H2S does not possess a bond angle of 104.5° as expected in a bent shape containing sp3 hybrid orbitals as per the VSEPR concept. Rather, the bent shape of H2S reduces the H-S-H bond angle from an ideal value of 109.5° to 92.1°.
Conversely, the H-S bond length is 133.6 pm in H2S.
As per Pauling’s electronegativity scale, a polar covalent bond is formed if the bonded atoms have an electronegativity difference between 0.4 and 1.6 units.
In H2S, an electronegativity difference of 0.38 units exists between the single-covalently bonded hydrogen (E.N = 2.20) and sulfur (E.N = 2.58) atoms.
0.38 units < 0.4 units, but as each H-S bond in the bent H2S molecule is composed of dissimilar atoms, so the comparatively more electronegative S-atom attracts the H-S electron cloud largely towards itself, away from the H-atoms.
As a result, the central S-atom gains a partial negative (δ-) charge while the terminal H-atoms obtain partial positive (δ+) charges.
The H-S dipole moments stay uncancelled in the asymmetric bent shape to yield an overall polar hydrogen sulfide molecule (net µ = 0.95 Debye).
FAQ
What is the Lewis dot structure of hydrogen sulfide (H2S)?
The Lewis dot structure of H2S displays a total of 8 valence electrons, i.e., 4 electron pairs.
A sulfur (S) atom is present at the center. It is single covalently bonded to two H-atoms, one on each side.
2 lone pairs of electrons are also present on the central S-atom in H2S.
How many lone pairs are present on the S-atom in H2S?
The hydrogen sulfide (H2S) molecule consists of a total of 2 bond pairs and 2 lone pairs. Both the lone pairs of electrons are present on the central S-atom.
So, the S-atom possesses 2 lone pairs in H2S.
What is the shape of the H2S molecule? Is it bent or linear?
The hydrogen sulfide (H2S) molecule possesses a bent, angular or V-shape.
Why is the shape of H2S different from its electron pair geometry?
The presence of 2 lone pairs of electrons on the central S-atom in H2S leads to strong lone pair-lone pair and lone pair-bond pair electronic repulsions. This strong repulsive effect distorts the shape and geometry of the molecule and makes it occupy a bent shape, different from its ideal electron pair geometry, i.e., tetrahedral.
Is H2S an ideal or a non-ideal molecular shape?
H2S possesses an asymmetric bent shape, thus a non-ideal molecular shape. Due to molecular distortion, the H-S-H bond angle is reduced to 92.1° from an ideal value of 109.5°.
What are the shapes of SiF4, PCl3, H2S, and CH3Cl?
SiF4and CH3Cl possess tetrahedral molecular shapes. To silicon or a carbon atom at the center, four atoms are covalently bonded, and there is no lone pair of electrons on the central atom.
In contrast, the shape of PCl3is trigonal pyramidal. To a phosphorus atom at the center, three Cl-atoms are attached, and the central P-atom also possesses a lone pair of electrons.
H2S possesses a bent, angular or V-shape. To a sulfur atom at the center, 2 lone pairs of electrons are attached, which distorts the overall molecular shape and geometry.
The greater the number of lone pairs on the central atom in a molecule, the stronger the electron repulsive effect and thus, the molecular shape gets distorted to a larger extent, reducing the internal bond angle.
Why is the bond angle in H2S smaller than that in H2O, although both possess a bent shape?
The bond angle in a molecule depends on the arrangement of bonding electrons around the central atom and the repulsion between these electron pairs.
In H2S, the central atom is sulfur (S), while that in H2O is oxygen (O). Sulfur (E.N = 2.58) has a higher radius and a smaller electronegativity value than oxygen (E.N = 3.44). This leads to weaker bonding between S-atom and H-atoms as opposed to O-atom and H-atoms. This weaker bonding interaction leads to less repulsion between bond pairs, resulting in a smaller bond angle.
The total number of valence electrons available for drawing the H2S Lewis structure is 8.
The molecular geometry or shape of H2S is bent, angular or V-shaped.
The ideal electron pair geometry of H2S is tetrahedral.
H2S does not possess any hybridization as per Drago’s rule.
The H2S molecule possesses a mutual bond angle of 92.1° between the bonded atoms.
H2S is a polar molecule as the small dipole moment values of H-S bonds stay uncancelled in the asymmetric, bent shape of the molecule.
Zero or no formal charges are present on the bonded atoms in H2S, which ensures the incredible stability of the Lewis dot structure obtained in this article.
Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/
2 thoughts on “H2S Molecular geometry or shape, electron geometry, Bond angle”
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Thanks for sharing the best information. I am really enjoying reading your well written articles.
Thanks!