The atom is considered to be the most basic building
block of all matter. Atoms are composed of three subatomic
particles. These three sub-atomic particles are:
protons, neutrons, and electrons. These three particles
will determine the properties of the specific atoms.
Elements are substances composed of the same atoms
with specific properties. Oxygen is an example of this.
The main property that defines each element is the
number of neutrons, protons, and electrons. Hydrogen
and helium are examples of elements. Both of these
elements have neutrons, protons, and electrons but differ
in the number of those items. This difference alone
accounts for the variations in chemical and physical
properties of these two different elements. There are
over a 100 known elements in the periodic table, and
they are categorized according to their properties on
that table. The kinetic theory of matter also states that
the particles that make up the matter are always moving.
Thermal expansion is considered in the kinetic
theory and explains why matter contracts when it is
cool and expands when it is hot, with the exception
of water/ice