Answer:
Intermolecular forces
Step-by-step explanation:
The force of attractions that act between molecules are called intermolecular forces.
Their nature is electromagnetic, this means that they are just an expression of the electromagnetic force.
One example of intermolecular force is the ionic bond: this type of bond occurs when there are two ions, one positively charged and the other one negatively charged, and they are attracted by each other due to the electrostatic force, which therefore creates a bond between them.
Other types of intermolecular forces include:
Hydrogen bond
Ion-dipole forces
Van der Waals forces
The strength of these intermolecular forces determine the state of the substance. In fact, in solids, these forces are very strong, so that the molecules are strongly bond to each other and they cannot move freely, but only vibrate about their fixed position. On the other hand, in gases, these forces are very weak, therefore the molecules are able to move freely away from each other.