The electron is bound to the nucleus by an electric force which acts somewhat like the gravitational force but is much stronger on small scales. However, for the electric force, opposite charges attract and like charges repel. The main difference between various chemical elements is the number of protons, neutrons, and electrons that each atom of the element possesses. Also, the distances from the nucleus and the energies of electrons in each atom are different from all other atoms. The Kelvin scale is based upon the absolute zero point where the velocity of gas atoms or molecules would be zero.
Pressure is defined as force per area.
For a gas enclosed in a container, the gas pressure is a measure of how many atoms hit the walls of the container and at what speed. The higher the temperature, the faster the atoms will be moving and so these atoms will hit the container walls more often thus increasing the pressure. Molecules A molecule is a bonding together of 2 or more atoms. The abundance of a particular molecule is dependent upon the temperature and pressure. High temperatures lead to more collisions between molecules which can cause them to dissociate or break-up into individual atoms.