Why do atoms of a feather flock together

[gib65]

Why isn't the universe just a big soup of chemicals? Why is it that when we find water, or dirt, or air, we find it with more water, dirt, or air. In other words, why not just a single water molecule by itself? Why do water molecules tend to stick around with other water molecules?

When we look around the world, we don't see one uniform substance making up everything--we see rocks, trees, sky, clouds, rivers, animals, and so on. In other words, different substances clumping together and staying separate from other substances. Take the sky for example. It is not only composed of oxygen, nitrogen, and carbon dioxide, but water molecules. Water molecules tend to clump together as clouds, separating itself from the rest. Of course, the rest of the molecules--the oxygen, nitrogen, and carbon dioxide--seem to stay evenly mixed (I think), but in general, there seems to be this tendency of molecules and atoms of one kind to stick together with other molecules and atoms of the same kind. The consequence is that, at the macroscopic level, we see objects made of specific substances separately from other objects made of different substances rather than a uniform soup of chemicals permeating everything.

Why do molecules and atoms do this?

[MigL]

Gravity provides for the general clumping together of matter.
This is then further sorted by density, temperature and pressure gradients, as well as intermolecular forces.
Did I miss any other sorting criteria ?

[Sensei]

1 hour ago, gib65 said:

Why do water molecules tend to stick around with other water molecules? 

That is simple. Water is polar molecule. i.e. one side of molecule has more positive charge (H⁺), while other side of molecule has the more negative charge (O^2-)

https://en.wikipedia.org/wiki/Chemical_polarity

(you have picture of water molecule and model of charge distribution in the above article)

 

[swansont]

6 hours ago, gib65 said:

Why isn't the universe just a big soup of chemicals?

It isn’t?

6 hours ago, gib65 said:

Why is it that when we find water, or dirt, or air, we find it with more water, dirt, or air. In other words, why not just a single water molecule by itself? Why do water molecules tend to stick around with other water molecules?

When we look around the world, we don't see one uniform substance making up everything--we see rocks, trees, sky, clouds, rivers, animals, and so on. In other words, different substances clumping together and staying separate from other substances. Take the sky for example. It is not only composed of oxygen, nitrogen, and carbon dioxide, but water molecules. Water molecules tend to clump together as clouds, separating itself from the rest. Of course, the rest of the molecules--the oxygen, nitrogen, and carbon dioxide--seem to stay evenly mixed (I think), but in general, there seems to be this tendency of molecules and atoms of one kind to stick together with other molecules and atoms of the same kind. The consequence is that, at the macroscopic level, we see objects made of specific substances separately from other objects made of different substances rather than a uniform soup of chemicals permeating everything.

Why do molecules and atoms do this?

Only some atoms do this. Noble gases don’t, and lots of combinations aren’t readily found in nature. Other combinations are. It depends on the bonds they are able to form.

After that, over time, materials congregate via processes known as differentiation. Density/gravity and chemistry play roles.

https://en.m.wikipedia.org/wiki/Planetary_differentiation