Along with liquids and solids, gases are one of the three major states of matter. Typically they result when a substance is heated in its liquid state to its boiling point, or when evaporation occurs from the surface of a liquid. There are numerous types and classifications of gases, including elements that naturally exist in a gaseous form, compound gases comprising more than one element, and mixtures of individual pure gases. Gas particles are much more loosely connected than those found in liquid or solid states, which results in lower density – and this is ultimately what sets a gas apart from the other two phases. Without changes in pressure or temperature, gas particles move around freely and randomly. They have no set shape and only change direction and momentum when bouncing off one another or off the inside of a container. Negatively charged areas of particles are attracted to positively charged areas – how these interact varies depending on the gas and are part of what makes each one unique. Because most gases are colourless, they are measured by four different properties: volume, temperature, pressure and number of particles; the latter property is more commonly known as moles. When put into a container (and not pressurised) gas molecules will evenly distribute themselves.
