Hydrogen sulfide is a chemical compound with the formula H₂S. It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs.
Hydrogen sulfide (H 2 S) structural formula includes two atoms of hydrogen (H) covalently bonded to one atom of sulfur (S). The compound has a bent molecular shape because of its bond angle of 92.1 degrees, and the sulfur atom contains two lone pairs of electrons.
The Lewis structure of hydrogen sulfide (H2S) can be described as follows:
Count the Total Number of Valence Electrons:
- Hydrogen (H) has 1 valence electron, and there are 2 hydrogen atoms: 2 x 1 = 2 electrons.
- Sulfur (S) has 6 valence electrons.
- Total valence electrons = 2 (from H) + 6 (from S) = 8 electrons.
Place the Least Electronegative Atom in the Center:
- Sulfur is less electronegative than hydrogen, so it goes in the center.
Arrange the Electrons Around the Atoms:
- Place two electrons between the hydrogen and sulfur to form covalent bonds. This uses 4 electrons (2 for each bond).
- You now have 4 electrons left.
Complete the Octet for Sulfur:
- Sulfur needs 8 electrons to fulfill the octet rule. It already has 4 from the bonds with hydrogen.
- Place the remaining 4 electrons as two lone pairs around sulfur.
So, the Lewis structure for H2S looks like this:
Here, each dot represents an electron, and the lines between H and S represent a single covalent bond, which consists of two electrons. Each hydrogen atom has its required 2 electrons (although in Lewis structures, we typically focus on octets), and sulfur has an octet with:
- Two bonding pairs (the lines to H atoms).
- Two lone pairs (the dots around S).
This structure shows that:
- The central sulfur atom is surrounded by 8 electrons (fulfilling the octet rule).
- Each hydrogen atom forms one covalent bond, achieving the electron configuration of helium which is stable with 2 electrons.
Remember, in this structure:
- The lines represent shared electron pairs (bonds).
- The pairs of dots represent unshared electrons or lone pairs on the sulfur atom.
Hybridization and Geometry
Hydrogen sulfide (H₂S) has the following characteristics regarding hybridization and molecular geometry:
Hybridization:
- Sulfur (S) Atom:
- The sulfur atom in H₂S undergoes sp³ hybridization.
- In its ground state, sulfur has an electron configuration of [Ne]3s²3p⁴. To form bonds with two hydrogen atoms and accommodate two lone pairs, sulfur mixes its 3s orbital and three 3p orbitals to form four sp³ hybrid orbitals.
Molecular Geometry:
- Shape:
- Despite sulfur’s sp³ hybridization, which would suggest a tetrahedral arrangement of electron pairs, the presence of two lone pairs on sulfur affects the geometry.
- The actual molecular geometry of H₂S is bent or V-shaped. This is because the lone pairs of electrons take up more space than the bonding pairs, causing the bond angles to be less than the ideal 109.5° for a regular tetrahedral arrangement.
- Bond Angle:
- The bond angle in H₂S is approximately 92.1 degrees. This deviation from the tetrahedral angle is due to the repulsion by the lone pairs, which compresses the H-S-H angle.
Explanation:
- Electron Pair Geometry: The arrangement of all electron pairs (both bonding and non-bonding) around sulfur is tetrahedral if we consider the electron pairs alone, but since we describe molecular geometry by the positions of atoms, not the lone pairs, we focus on the shape formed by the atoms.
- Effect of Lone Pairs: The two lone pairs on sulfur not only dictate the geometry by repelling the bonding pairs but also contribute to the molecule’s bent shape. Lone pairs exert greater repulsive forces than bonding pairs, hence reducing the bond angle.
So, in summary:
- Hybridization: sp³ on the sulfur atom.
- Molecular Geometry: Bent or V-shaped.
- Electron Pair Geometry: Tetrahedral (if considering all electron pairs, both bonding and lone pairs).