| Temperature
Learn
about how temperature measures the average energy of motion
of particles that make up a substance.
Substances
Substances differ greatly in mass, volume, shape, density,
texture, reaction to temperature and light, and in many other
ways. Most substances can exist in different states or phases.
A substance loses or gains energy when changing from one form
of phase to another phase. Temperature is a measure of the
average energy of motion of the particles that make up the
substance.
Particles
and Solid
Particles in a solid have less average thermal energy than
the particles in its liquid or gaseous form. In the solid
state the particles are close together, usually in orderly
arrangements. If the temperature of a solid is increased,
its atoms or molecules tend to move farther apart and can
slide past one another while still remaining loose but still
connected. At this point, the solid becomes a liquid.
Liquid
again
This property of liquids allows them to flow. If enough additional
energy is added to a liquid, the forces of attraction between
atoms and molecules can be overcome and the particles can
move freely in the gas phase.
Elements
Other substances are made up of two or more different elements
in which the atoms group together to form molecules. A substance
that is made up of the same molecules is a compound. Substances
can undergo physical changes that only alter the shape, form,
volume, or density of the material but produce no change in
chemical composition. Substances can also undergo chemical
changes that produce new substances with different characteristics.
Physical changes do not bring about the alterations in the
properties of matter that chemical changes do.
Atoms
equal water
Different kinds of atoms can combine to form simple molecules
of substances, such as water (show at the bottom).
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