Liquid water – made from two types of gas. Makes no sense to me, whatsoever. Water seems to be one of the strangest substances and we completely take it for granted that, apparently, it’s made of gas!
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In a gas, molecules fly around freely, with very little interactions between them. In a liquid, molecules are bound together. These bonds break very easily and are in fact broken and reformed all the time. If the bonds were stronger, it would be a solid.
Molecules will tend to stick together for various reasons. For example, hydrogen atoms easily form weak bonds with atoms on the right of the periodic table, like oxygen, fluor… These bonds are called “hydrogen bonds”. (Note that these are bonds between atoms of different molecules. They’re different from the bonds between atoms that form molecules, which are a lot stronger and are called “covalent bonds)
If you have water, hydrogen atoms and oxygen atoms in the water molecules will be attracted to each other. The molecules will stick together and form a liquid. If you have only hydrogen (or only oxygen), they won’t form such bonds and so they will wander freely, forming a gas.
You can give water molecules some energy, by heating them, so that they break these bonds and wander freely too (at 100°C). You can also remove energy from dioxygen molecules, by cooling them, so that they don’t have enough speed, settle down and form a liquid (at around -183°C). But it takes much more energy to break the bonds between water molecules than to break the bonds between dioxygen molecules, so that’s why you have to heat water a lot more to obtain a gas.
Side note : it’s not only water. The boiling point of a molecule doesn’t depend on the boiling point of its atoms. For example, alcohol (named “ethanol” by chemists) is liquid at ambient temperature, but is composed of carbon, hydrogen and oxygen. Carbon is a solid at ambient temperature (it can be the graphite of your pencils, or diamonds), and hydrogen and oxygen are gases.
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