H2S Bonding & Structure (Polarity Guide)
H₂S is polar. Sulfur has eight valence electrons to place in its Lewis structure, forming two single bonds to hydrogen and keeping two lone pairs. These four electron domains give a tetrahedral electron-domain arrangement, but the molecule itself is bent. The S–H bond dipoles therefore do not cancel; their combined effect points toward sulfur.
It is easy to see two matching S–H bonds and assume their effects cancel. That conclusion misses a key step: you must consider the molecule’s shape, not just its bonds. In this guide, I’ll build the structure, use VSEPR to find the shape, and then add the bond dipoles to decide whether H₂S is polar.
A useful way to check your reasoning is to ask three questions in order: How many valence electrons are there? What shape do the atoms form? Do the bond dipoles cancel in that shape? Each question builds on the one before it.
H₂S bonding: Lewis structure and valence-electron count
A Lewis structure shows how valence electrons are arranged in bonds and lone pairs. For hydrogen sulfide, H₂S, count the electrons first, then place two hydrogen atoms around sulfur. The final structure has two S–H single bonds and two lone pairs on sulfur.
Sulfur is in Group 16, so it contributes six valence electrons. Each of the two hydrogen atoms contributes one. That gives a total of eight valence electrons:
| Atom | Number of atoms | Valence electrons per atom | Total |
|---|---|---|---|
| Sulfur (S) | 1 | 6 | 6 |
| Hydrogen (H) | 2 | 1 | 2 |
| Total | 8 |
To draw the structure, put sulfur in the middle and connect each hydrogen to it with a single bond:
H–S–H
Each single bond uses two electrons. The two bonds use four electrons in total, leaving four electrons. Place those remaining electrons on sulfur as two lone pairs. In a simple Lewis drawing, each lone pair is shown as two dots beside S.
The electron count now checks out: four electrons in the bonds plus four in the lone pairs equals eight. Each hydrogen shares one bond and has access to two electrons, which fills its first shell. Sulfur has four shared pairs around it, giving it an octet in this Lewis model.
The formal charges are zero in this structure. Formal charge is a bookkeeping check that compares an atom’s usual valence count with the electrons assigned to it in a Lewis structure. A zero formal charge on each atom supports the arrangement shown.
Check: two bonds, two lone pairs, eight total valence electrons, and zero formal charges. That gives the structure needed to work out the shape.
VSEPR and the bent shape of H₂S
VSEPR is a model used to predict molecular shape. It treats a bond or lone pair around a central atom as an electron domain. H₂S has four domains around sulfur: two S–H bonds and two lone pairs. The domains arrange roughly tetrahedrally, while the atoms form a bent molecule.
VSEPR classifies H₂S as AX₂E₂. In this label, A is the central sulfur atom, X₂ means two atoms are bonded to it, and E₂ means two lone pairs sit on it.
This notation helps distinguish two shapes that are often mixed up:
- Electron-domain geometry: the arrangement of all four domains around sulfur. It is tetrahedral.
- Molecular shape: the arrangement of the atoms only. H₂S is bent because its two hydrogen atoms do not lie in a straight line.
The difference matters because lone pairs affect the space around sulfur even though they are not atoms in the molecule’s outline. So “tetrahedral” describes the four electron domains, not the shape made by H and S atoms.
The H–S–H bond angle is about 92°. H₂S is therefore bent, not linear. The basic VSEPR model helps identify the shape, but it does not give this exact angle on its own. The measured angle is much smaller than the ideal tetrahedral angle of about 109.5°.
| What you are describing | H₂S result | What it includes |
|---|---|---|
| Electron-domain geometry | Tetrahedral | Two bonds and two lone pairs |
| Molecular shape | Bent | Sulfur and two hydrogen atoms |
| H–S–H bond angle | About 92° | Angle between the two S–H bonds |
| VSEPR label | AX₂E₂ | Two bonded atoms and two lone pairs |
Check: use “tetrahedral” for the electron domains and “bent” for the molecular shape. The bent shape is the key to deciding whether the dipoles cancel.
S–H bond dipoles and molecular polarity
A bond dipole is a shift in shared electrons caused by a difference in electronegativity. Sulfur is more electronegative than hydrogen, so each S–H bond dipole points toward sulfur. Because the H₂S molecule is bent, these two dipoles do not cancel, making the whole molecule polar.
Electronegativity describes how strongly an atom attracts shared electrons in a bond. On the Pauling scale, sulfur’s value is about 2.58, while hydrogen’s is about 2.20. The difference is modest, but it means the shared electrons in each S–H bond are drawn more toward S.
A dipole arrow points toward the more electronegative end of a bond. For each S–H bond, that end is sulfur. You can picture one arrow along each bond, pointing from H toward S.
To decide whether H₂S as a whole is polar, consider both arrows as vectors. A vector has both size and direction. In a bent molecule, the sideways parts of the two matching dipoles balance each other, but the parts pointing toward sulfur add together. The result is a net molecular dipole toward S, along the angle bisector.
This explains an important distinction:
- Polar bonds have uneven sharing of electrons.
- A polar molecule has an overall dipole after all bond dipoles are added.
Polar bonds do not always make a polar molecule. A molecule can have polar bonds whose dipoles cancel because of its shape. In H₂S, the bonds are polar and the shape prevents cancellation, so the whole molecule is polar.
Check: sulfur attracts the shared electrons more strongly, each bond dipole points toward S, and the bent geometry leaves a net dipole. Therefore, H₂S is polar.
A step-by-step polarity check for H₂S
A polarity check is a short sequence that links the Lewis structure to the final answer. It prevents a common error: deciding that a molecule is nonpolar just because it has two identical bonds. For H₂S, follow the steps in order and use the shape before judging cancellation.
Here is a complete worked analysis:
- Count valence electrons. Sulfur contributes six, and two hydrogens contribute two more. Total: eight.
- Draw the Lewis structure. Make two S–H single bonds and place the remaining four electrons as two lone pairs on sulfur.
- Count electron domains. Sulfur has two bonding domains and two lone-pair domains. The VSEPR label is AX₂E₂.
- Name both geometries. The domains are arranged tetrahedrally; the atoms form a bent shape with an angle near 92°.
- Find the bond-dipole directions. Each dipole points from hydrogen toward sulfur because S is more electronegative.
- Add the dipoles. They do not cancel in a bent arrangement. H₂S has a net dipole and is polar.
Consider a common student answer: “The two S–H bonds are the same, so H₂S is nonpolar.” The bonds are indeed identical, but that fact alone does not settle the question. Identical dipoles cancel only when their directions and molecular arrangement make their vector sum zero.
I use a simple diagnostic question when checking this kind of answer: “If you drew both arrows, would they point in opposite directions along one line?” For H₂S, they would not. The arrows point toward sulfur from two different directions, so their effects add rather than cancel.
| Diagnostic question | H₂S answer | What it tells you |
|---|---|---|
| Are the S–H bonds polar? | Yes | Electronegativity differs |
| Which way does each dipole point? | Toward S | Sulfur attracts shared electrons more strongly |
| Is H₂S linear? | No, it is bent | The bond dipoles are not opposite |
| Do the bond dipoles cancel? | No | A net molecular dipole remains |
| Is the molecule polar? | Yes | The net dipole is not zero |
Comparing H₂S with a linear molecule
A comparison with carbon dioxide shows why bond polarity and molecular polarity are separate questions. CO₂ has polar C=O bonds, but its linear, symmetric shape makes the bond dipoles cancel. H₂S has two polar bonds too, but its bent shape leaves a net dipole.
| Feature | H₂S | CO₂ |
|---|---|---|
| Central atom | Sulfur | Carbon |
| Bond arrangement | Bent | Linear |
| Bond dipoles | Point toward sulfur | Point toward oxygen |
| Do the dipoles cancel? | No | Yes, because they point in opposite directions |
| Molecular polarity | Polar | Nonpolar |
The comparison is a useful test of your method. Do not stop after you identify polar bonds. First draw or infer the shape, then ask whether the dipoles cancel in that arrangement.
Takeaway: molecular polarity depends on both bond polarity and geometry. Same or different bonds alone do not give the complete answer.
Frequently asked questions about H₂S polarity
These quick answers review the points most often needed when identifying the structure and polarity of hydrogen sulfide. Use them as a final check: count the electrons, keep electron-domain geometry separate from molecular shape, and use dipole directions to decide whether the molecule has a net dipole.
Is H₂S polar or nonpolar?
H₂S is polar. Its two S–H bond dipoles point toward sulfur, and the bent molecular shape prevents them from canceling.
What is the Lewis structure of H₂S?
Sulfur is in the center, with a single bond to each hydrogen. Sulfur also has two lone pairs.
How many valence electrons does H₂S have?
H₂S has eight valence electrons: six from sulfur and one from each of its two hydrogen atoms.
What is the VSEPR notation for H₂S?
The VSEPR notation is AX₂E₂. It represents two bonded atoms and two lone pairs around the central sulfur atom.
Is H₂S tetrahedral?
Its electron-domain geometry is tetrahedral. Its molecular shape, which describes the positions of the atoms, is bent.
What is the H–S–H bond angle?
The H–S–H angle is about 92°. This confirms that the molecule is bent, not linear.
Which way do the S–H bond dipoles point?
They point toward sulfur. Sulfur has a higher Pauling electronegativity than hydrogen, so it attracts the shared electrons more strongly.
Why don’t the two S–H dipoles cancel?
The bonds meet at an angle in the bent molecule. Their dipoles therefore point in different directions and leave a net dipole toward sulfur.
Can a molecule have polar bonds but be nonpolar?
Yes. If the molecule’s shape places its bond dipoles so they cancel, the molecule can be nonpolar, as CO₂ illustrates.
Final answer: why H₂S is polar
To explain H₂S polarity, connect three facts: its Lewis structure has two S–H bonds and two sulfur lone pairs; its shape is bent, with an H–S–H angle near 92°; and sulfur attracts the shared electrons more strongly than hydrogen. The bond dipoles point toward sulfur and do not cancel. That is why H₂S is polar.
(This article was written by one of our staff writers, Alan Westbrook. Visit our Meet the Team page.)
