We can classify the things we work with in
science into several broad catagories. First, we can seperate out pure
substances from mixtures:
- Pure substances: these have a
fixed composition and set of physical properties.
- Mixtures: two or more pure
substances mixed together.
We can further divide each of the
catagories above into two subgroups.
- Elements: any matter that cannot
be broken down into further pure substances. The elements are listed
on the periodic table: we currently know of about 115. Iron and
uranium are elements
- Compounds: pure substances made
up of one or more elements with a fixed composition. Methane is a
compound: it is made up of four hydrogen atoms and 1 carbon atom. (CH4)
- Homogeneous: a homogeneous
mixture is one that has the same composition throughout. Sea water is
a homogeneous mixture of water, table salt and a variety of other
compounds, stainless steel is a homogeneous mixture of iron, carbon,
nickel and other elements.
- Heterogeneous: nonuniform
mixtures. Dirt is a heterogeneous mixture of soil, rocks, worms and