All matter
is made from atoms with the configuration of the atom, the number of protons,
neutrons, and electrons, determining the kind of matter present (oxygen, lead,
silver, neon ...). Every substance has a unique number of protons, neutrons,
and electrons. Oxygen, for example, has 8 protons, 8 neutrons, and 8 electrons.
Individual atoms can combine with other atoms to form molecules. Water
molecules contain two atoms of hydrogen H and one atom of oxygen O
and is chemically called H2O. Oxygen and nitrogen, which are the major
components of air, occur in nature as diatomic (two atom) molecules.
Regardless of the type of molecule, matter normally exists as either a solid,
a liquid, or a gas. We call this property of matter the state of the
matter. The three normal states of matter have unique characteristics which are
listed on the slide.
Solid
In a solid
the molecules are closely bound to one another by molecular forces. A solid
holds its shape and the volume of a solid is fixed
by the shape of the solid.
Liquid
In a liquid
the molecular forces are weaker than in a solid. A liquid will take the shape
of its container with a free surface in a gravitational field. In microgravity,
a liquid forms a ball inside a free surface. Regardless of gravity, a liquid
has a fixed volume.
Gas
In a gas
the molecular forces are very weak. A gas fills its container, taking both the
shape and the volume of the container.
Fluids
(Liquids and Gases)
Liquids and
gases are called fluids because they can be made to flow, or move. In
any fluid, the molecules themselves are in constant, random motion, colliding
with each other and with the walls of any container. Any substance can occur in
any state. Similarly, if we heat a volume of water
above 100 degrees Celsius, or 212 degrees Fahrenheit, water changes its state
into a gas called water vapor. Changes in the state of matter are physical
changes, not chemical changes. A molecule of water vapor has the same
chemical composition, H2O, as a molecule of liquid water or a molecule
of ice.
Plasma -
the "fourth state"
The three
normal states of matter listed on the slide have been known for many years and
studied in physics and chemistry classes. In recent times, we have begun to
study matter at the very high temperatures and pressures which typically occur
on the Sun, or during re-entry from space. The resulting mixture of neutral
atoms, free electrons, and charged ions is called a plasma. A plasma has
some unique qualities that causes scientists to label it a "fourth
state" of matter. A plasma is a fluid, like a liquid or gas, but because
of the charged particles present in a plasma, it responds to and generates
electro-magnetic forces.
MASS
TEMPERATURE
OBSERVATIONS AND MEASUREMENTS
