Phases of matter

Matter can be a solid, liquid, gas, or plasma—four of the phases of matter—depending on its temperature. In the kinetic theory, the phase of matter for a particular substance is related to the average thermal energy of its atoms or molecules. At any given temperature, the phase of a material depends on the strength of the attractive forces that pull atoms and molecules together compared to the chaotic agitation of thermal motion.
Motion of particles in the gas phaseIn a gas the thermal motion of atoms completely overcomes attractive forces between molecules. Molecules in a gas are typically far apart from each other. Water becomes a gas above its boiling point of 100ºC. Of the three phases, gas has the highest kinetic energy per molecule and occurs at the highest temperature. Read the text aloud
Motion of particles in the liquid phaseBetween 0ºC and 100ºC water is a liquid. Molecules in a liquid have enough thermal energy to break away temporarily from their neighbors and change places with one another, but liquid molecules do not have enough thermal energy to separate completely and become a gas. Liquids flow because molecules can change places with their neighbors. Read the text aloud Show van der Waals forces
Motion of particles in the solid phaseBelow 0ºC water is a solid. Matter becomes solid when thermal energy is too low to overcome intermolecular forces. Molecules in a solid are still vibrating, but an average molecule does not have enough energy to break away from its immediate neighbors or to exchange places with another molecule. That is why solids hold their shape. Read the text aloud
Plasma is a less well know phase of matter. We don't regularly come in contact with plasma, due to the high temperatures required (10,000 K for a hydrogen atom and even higher temperatures for other atoms!). The plasma phase occurs when a gas is at a temperature high enough that some (or all) of the electrons break free form their atoms or molecules. Speeding around in a plasma are both (negatively charged) free electrons and the rest of the atoms (the positively-charged ions). Plasma is a good conductor of electricity, can block some wavelengths of light, and, because it is composed of charged particles, can be manipulated by both electric and magnetic fields. Show Examples of plasmas
It takes energy to be absorbed by a solid for it to melt into a liquid. Similarly, energy is absorbed by a liquid to evaporate it into a gas. This is known as an endothermic process. Conversely, an exothermic process occurs when energy is released, such as when a gas condenses back into a liquid or when a liquid freezes back into a solid.

Which common phase of matter has the weakest intermolecular forces?

  1. solid
  2. liquid
  3. gas
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