What is gas?

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.