It is a magnetic force between the molecules or the space between these molecules. These forces can be cohesive, in simple words the force is between similar molecules and there is also adhesive force, which is the force between unlike molecules. There are some forces which are arranged according to their reducing strength, and they are ionic interactions, hydrogen bonding, dipolar molecule and Van Der Waals forces.
Ionic interactions are likely between the ions, they usually move away or repel from like ions and there is great attraction towards the opposite ions. While hydrogen bonding is basically the bonding of a number of electron pairs that are shared by small electromagnetic atoms such as nitrogen, oxygen etc. Van Der waal which is also known as dipole-dipole interaction, and is a force which occurs between two molecules with strong or permanent dipole. These are the basic fundamentals of intermolecular forces. They are basically described by Coulomb's law. But the basic difference between them is their charges.
The attraction between the molecules is much weaker than the attraction between the atoms within a molecule. In a molecule of HCL, there is a covalent bond between H and CL which is due to the mutual sharing of electrons. Both atoms satisfy their outermost shells and it is their firm need to remain together, hence this linkage is very strong.
HCL molecules in the neighbourhood attract each other, but the forces of attraction are weak. These forces are believed to exist between all kinds of atoms and molecules when they are sufficiently close to each other. Such intermolecular forces are called van der waals forces and they have nothing to do with the valence electrons. These intermolecular forces bring the molecules close together and give particular physical properties to the substances in gaseous, liquid and solid states. There are four types of such forces.
1. Dipole-dipole forces
2. Ion-dipole forces
3. dipole-induced dipole forces
4. Instantaneous dipole-induced dipole forces or London dispersion forces.
In nature two molecule of any atom attract or repel each other which result in intermolecular forces to bind them together as an atom. These forces determine the physical state of an atom i.e. Solid liquid gas and their respective properties. In like molecules of any atom these are cohesive forces (surface tension) and in unlike atom molecules they are adhesive (capillary action). These forces are categorized according to their interaction type (electrostatic/electrodynamics) i.e. (1) Ionic interaction (electrostatic): This interaction takes place b/w the ions (positive and negative) of an atom and result in Ionic (bond) compounds. These compound exhibit high melting, boiling points and are good conductor of electricity. Example is bond between sodium (Na) and chloride (Cl) ions in salt (NaCl). (2) Intermediate dipole-dipole attraction (electrostatic): This interaction includes bonding between partial positive and partial negative charged ions e.g. Bonding between hydrochloric acid (HCL) (3) Vander Waal's forces (electrodynamics): These forces come into play when attraction between induced dipole and non polar molecules occur resulting in bond formation e.g. Reaction of chlorine in water (4) Hydrogen bonding (electrostatic): This bonding take place when hydrogen atom (partial positive ion) is bond to electronegative atom. Water is major example of this bonding besides it is abundantly found in nature. This is strong and directional bonding.
In which state does carbon dioxide show the strongest intermolecular forces, gas or solid?