At low temperatures, the atoms and molecules stick together. Why is this?

Question

why do atoms and molecules clump together at low temperature?

Answer 1

There are weak inter-atomic and inter-molecular forces that attract the atoms and molecules.  If the atoms and molecules are moving fast, those weak forces cannot keep them together.  At low temperature, the atoms and molecules move slowly.  They move faster at higher temperatures.  If the temperature is low enough, the weak attractive forces may draw them together.