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Chemistry is the study of matter and
its changes and interactions. Matter is anything that
has mass and takes up space. There are two broad
categories of matter�Pure Substances and Mixtures.
Pure Substances
Elements and compounds are both pure substances. A pure substance
is when each particle is identical. Elements have each atom the
same and compounds have each molecule the same. Compounds are atoms
of more than one element chemically bonded together.
Mixtures
Mixtures are more than one type of pure substance physically mixed
together. Mixtures can be categorized into homogeneous and
heterogeneous. Homogeneous mixtures (also called solutions) look
the same throughout; while heterogeneous have visible different
types of matter.
Energy
Energy is the ability to produce heat or do work. There are two
types of energy: Potential energy (or stored energy) and kinetic
energy (energy due to motion).
Changes
Chemical changes produce a new substance while physical changes do
not. Changes in state (melting, freezing, boiling, condensing,
etc.) are physical changes. Dissolving is also a physical change,
although it is often confused for a chemical change. Reacting with
another type of matter, burning or rusting are examples of chemical
changes. Often confused changes are melting (changing a solid to a
liquid by adding heat), burning (chemically reacting with oxygen)
and dissolving (combining two types of matter physically to produce
a mixture). Mixtures can be separated by physical changes,
compounds must be separated by chemical changes and elements cannot
be separated by either.
Scientific Processes
There are many paths to follow when undertaking �science��there is
no one scientific method. Science involves observing, posing
questions, forming possible explanations (hypothesis),
experimenting, processing/analyzing data, looking for trends, more
formation of possible explanations or question posing. Scientific
processes form theories (which attempt to explain observed behavior)
and laws (which describe or predict behavior, and are usually
mathematical). A theory cannot become a law�one explains why and
one describes what. A hypothesis is a proposed explanation for why
something will occur (that may become a theory with enough
evidence), while a prediction is simply a guess at what will
happen�it does not attempt to say �why� it will happen.
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