Hydrogen Bond - Why H2O Is A Liquid (water) And H2S Is A Gas?

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Learn more about Teams Why H2O is a liquid (water) and H2S is a gas? Ask Question Asked 6 years, 11 months ago Modified 6 years ago Viewed 35k times 2 $\begingroup$

I always think about this question. Is it due to attraction or repulsion or is there something else that makes one of them a gas and the other a liquid (water)?

• hydrogen-bond

Share Cite Improve this question Follow edited Nov 28, 2017 at 19:03 daniel 99477 silver badges2222 bronze badges asked Nov 28, 2017 at 18:41 user55439user55439 8911 gold badge22 silver badges99 bronze badges $\endgroup$ 1

• $\begingroup$ related chemistry.stackexchange.com/questions/63380/… $\endgroup$ – Mithoron Commented Nov 28, 2017 at 20:28

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The reason is hydrogen bonding.

The relatively large electronegativity difference between oxygen and hydrogen (about 2.3) is the reason why the partially positively charged (try to think why they are partially positively charged) hydrogens are attracted to the lone pairs on the oxygen atoms of other water molecules.

The relatively smaller electronegativity difference between sulphur and hydrogen (about 0.5) is too small to polarise the covalent bond to a required extent. Secondly, the lone pairs on the sulphur atom are delocalised in the sp3 orbitals and the d orbitals - an option unavailable to oxygen. So, the “negative charge” of the lone pairs is also distributed and the interaction is lowered.

So, the hydrogen bonding in water causes the water molecules to be associated with each other due to intermolecular forces of attraction, whereas in the case of hydrogen sulphide, these forces of attraction area much weaker.

So, lesser energy is required to overcome the forces of interaction between the hydrogen sulphide molecules than those between water molecules. This energy is available at room temperature and hence, hydrogen sulphide is a gas, while water is still a liquid.

Share Cite Improve this answer Follow answered Nov 28, 2017 at 20:07 Eashaan GodboleEashaan Godbole 1,5261111 silver badges2525 bronze badges $\endgroup$ 0 Add a comment | 1 $\begingroup$

In water molecule the more electronegative oxygen atom has small size and is present as a central atom, so that it forms the intermolecular hydrogen bonding strongly.

However, in $\ce{H2S}$ molecule the central atom sulfur is less electronegative and is bigger in size, so that it is unable to form the intermolecular hydrogen bonding.

Therefore $\ce{H2S}$ molecule can not exist in liquid form.

Share Cite Improve this answer Follow edited Dec 18, 2017 at 5:06 andselisk♦ 38.4k1414 gold badges133133 silver badges223223 bronze badges answered Dec 18, 2017 at 2:12 Priyabrata padhiPriyabrata padhi 1111 bronze badge $\endgroup$ 1

• 1 $\begingroup$ This is pretty much the same answer as the earlier one with the essential details stripped off. $\endgroup$ – andselisk ♦ Commented Dec 18, 2017 at 5:29

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Well, first of all depends on what temperature you are considering. But let’s take room temperature (20 degrees). In Water, the oxygen atom is highly electronegative and can polarize (partially) the hydrogen atoms, thus hydrogen-hydrogen bonds between the H2O molecules can be formed creating a very high boiling point. In H2S those bonds don’t exist, because sulfur is much less electronegative. Secondly, the lone pairs on the sulphur atom are delocalised in the sp3 orbitals and the d orbitals - an option unavailable to oxygen. So, the “negative charge” of the lone pairs is also distributed and the interaction is lowered.

So, the hydrogen bonding in water causes the water molecules to be associated with each other due to intermolecular forces of attraction, whereas in the case of hydrogen sulphide, these forces of attraction area much weaker.

So, lesser energy is required to overcome the forces of interaction between the hydrogen sulphide molecules than those between water molecules. This energy is available at room temperature and hence, hydrogen sulphide is a gas, while water is still a liquid.

Share Cite Improve this answer Follow edited Nov 28, 2017 at 19:23 answered Nov 28, 2017 at 19:12 TheChemistTheChemist 48822 silver badges1313 bronze badges $\endgroup$ 3

• $\begingroup$ "In H2S does bonds don’t exist, because sulfur is much electro negative. " That doesn't make any sense: $\ce{O}$ is more electronegative than $\ce{S}$. $\endgroup$ – Gert Commented Nov 28, 2017 at 19:21
• $\begingroup$ @Gert true, I might have a moment there where I skipped the thought $\endgroup$ – TheChemist Commented Nov 28, 2017 at 19:24
• $\begingroup$ Not "hydrogen-hydrogen bonds". They,re just hydrogen bonds", said once, and they are between hydrogen and a much more electronegative element with compact atoms (typically N, O, or F). $\endgroup$ – Oscar Lanzi Commented Nov 28, 2017 at 19:30

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