In the same conditions of course.
In: Chemistry
Water is a polar molecule. Oxygen is very electro-negative, meaning it pulls electrons close to it whenever it can. This means that the electrons in H2O spend most of their time near the oxygen atom, creating a positive charge near the Hydrogen atoms and a negative charge near the Oxygen.
This is what gives water many of its unique properties. Water molecules will attract one another and create weak hydrogen bonds. Those bonds are strong enough to pull the molecules close enough together that they condense into a liquid at room temperature.
Other atoms/molecules of similar molecular weights don’t have this property, so they don’t condense at room temperature.
Well, they’re very different molecules. There’s no reason to expect O2 to act anything like singlet O or O3 because the bulk properties don’t really care what the specific element is – just what the molecule is.
In the case of H2O the very polar bonds between H and O create unbalanced electric charge, and so similarly to a bucket of magnets the molecules start to align with one another and clump together.
The phase of a substance has to do with its intermolecular forces balancing. In other words, how much the molecules are attracted to each other vs repelled by each other.
But that’s much less important than what I think the main misunderstanding posed by the question, which has false equivalence – it’s like asking why chlorine gas is poisonous, and sodium explodes in water, but table salt is safe. The properties compounds are not decided by the elements they’re comprised of.
As a general rule, the properties of an element are often *very* different from the properties of its compounds, just as compounds are very different from each other. We drink H2O to keep ourselves alive, but drinking H2O2 would be harmful or fatal – that difference of one extra hydrogen atom bonded completely changes the properties of the compound.
In the case of water, the thing that makes it a liquid at room temperature is called *hydrogen bonds*. In each water molecule, one side of the molecule has a slight negative charge (near the O) and the other sides (near the H’s) have a slightly positive charge. This attracts water molecules to each other slightly – not enough for a true chemical bond, but enough to change the way that they interact. With enough heat energy, these small bonds won’t hold, and water will boil into steam. But at room temperature, they’re strong enough to give water a liquid state, bonded more closely together. A very similar molecule, H2S, has a much weaker negative charge on the S side, and so it winds up being a gas at room temperature, because the forces aren’t strong enough to hold it in a liquid state, like H2O.
Physics be weird!
Specifically, the main reason for this is that H2 and O2 have pretty low intermolecular cohesion: that is to say, a molecule of H2 doesn’t feel a very strong pull towards other nearby molecules of H2, and similar for O2. H2O on the other hand, actually has very strong intermolecular forces; it is a polar molecule, which means that when it is around other polar molecules they hug together tightly.
The other big factor that comes into play is molecular weight. Larger, heavier molecules and atoms like, say, iron, are solid because they are heavy, so it takes a lot more energy to make them start jiggling around to the point where they become a liquid, and even more energy to turn them into a gas. H2 is extremely light, so it doesn’t take a lot of energy to make it into a gas.
It’s important to recognize that when we say “H2 is a gas” what we actually mean is “H2 is a gas at room temperature and standard atmospheric pressure”. If the atmospheric pressure was really high, H2 might be a liquid, or even a solid! Similar to if the temperature was really low; hydrogen becomes a liquid at -252C while oxygen becomes a liquid at -297 C. Even if the air around you might feel chilly, it still actually has a pretty large amount of energy in it, at least compared to the vacuum of deep space or absolute zero. The conditions on the surface of the Earth just happen to result in certain substances being in particular states, like how water can be either a solid, liquid, or gas, depending on where you are on the surface, while gallium is only a liquid metal in warm areas, not cold areas like the arctic, and nowhere on the surface is hot enough to make gallium a gas. On some very cold planets we might expect it to rain H2 instead of water; on Saturn’s moon Titan, for instance, we think it probably has the right conditions that instead of a ‘water cycle’ of evaporation and precipitation it has a methane or ammonia cycle.
The state of matter is determined by how the molecules in the substance are attracted to each other. H2 and O2 are non polar molecules, so they don’t have a particular charge on one end, so there isn’t much intermolecular attraction. Water, however, is a polar molecule. The hydrogen has a slightly positive charge because all of the electrons stay close to the oxygen atom, giving it a slightly negative charge. The hydrogens from one molecule get pulled towards the oxygen of another molecule, resulting in a strong attraction between different molecules. Not strong enough to be a solid, but strong enough to not be a gas.
H20 is built like a magnet (called a polar molecule). The O atom attracts the electrons of the 2 H atoms, si the O side is negative (-) and the H side is positive (+), so they tend to stick togheter and don’t want to move around so much at room temperature, so they don’t become a gaz.
O2 (same for H2) have their electrons (-) are equally tempted to go the either of the O atoms, so no side is more negative than the other. They don’t have a tendency to stick to each other, so at room temperature, the molecules move fast enough to be gaseous.
Note : Many other characteristics can make a molecule gaz or liquid (for example, the size of the molecule, bigger molecules tend to have higher evaporation temperature), this is just one of the reasons.
Water is weird. H₂O has MUCH stronger bonds between molecules because it is polar.
Hydrogen has far less desire to attract electrons than oxygen so it is more electronegative. It fulfils this partly by bonding with the hydrogens, “sharing” their electrons.
Because of its electron configuration, the bond between oxygen and hydrogen is angled (the molecule is not a straight line). So the oxygen part of the molecule attracts electrons more than the hydrogen ends.
Because of this it can attract forces not only strongly with its own molecule’s hydrogens but weakly with those of other molecules.
The molecules being attracted together means it is a liquid. Because H₂O is attracted to many organic molecules it is also a good solvent and essential for life.
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