reading this section you will be able to do
basic definition of matter.
All matter such as solids, liquids,
and gases, is composed of atoms. Therefore, the atom is considered
to be the basic building block of matter. However, atoms are almost always
grouped together with other atoms to form what is called a molecule.
Only a few gases such as helium are composed of individual atoms
as the structural unit.
Atoms are extremely small. The radius
of a typical atom is on the order of 0.00000000001 meter and cannot
be studied without very powerful microscopes. In the image below
you can see how a scanning electron microscope can be used to
magnify things until very small details appear relatively big.
next two sub-units you will learn about what a material
composed of only one type of atom is called and you will look
at the basic model of an atom.