Science Background
Matter 5.4
Everything in the world is made of stuff that we call matter. Every
physical thing that you can think of is made of matter: a tree, a rock,
dirt, air, gasoline, everything. Matter is defined as anything that takes
up space and has mass (weight).
Atoms and Molecules
All matter is made up of tiny particles called atoms, which in turn form molecules. There
are 94 naturally occurring atoms that we have discovered to this day and about a dozen
others that scientists can create. The different atoms are called elements and they are
organized into a chart called the periodic table. Atoms are too small to see, even with an
electron microscope. Our understanding of atoms is based on models that scientists have
developed over time.
Here’s a diagram for you to check out:
Atoms are made of three types of particles.
Protons have a positive charge. They are
found in the center (the nucleus) of the
atom. Atoms are organized on the periodic
table by the number of protons that they
have. This model is helium, which is
number 2 on the periodic table and has two
protons.
Neutrons have no charge. They are also
found in the nucleus.
Electrons have a negative charge and they orbit the nucleus. In more complex models,
the electrons are organized at different levels of orbit.
Most atoms have the same number of each kind of particle. Oxygen has 8 protons, 8
neutrons and 8 electrons. Electrons can jump from one atom to another, usually from
atoms that have more electrons than protons to atoms that have more protons than
electrons. You’re already familiar with this movement of electrons – it’s called
electricity.
Atoms don’t just hang out by themselves. They bond together to form molecules.
¸ Molecules made of more than one kind of atoms are called compounds.
¸ Molecules made of only one kind of atom are called elements.
One molecule that we all know is H2O, the chemical name for water. All molecules have
chemical names made from the periodic table symbols of the atoms that form them.
Take a look:
H2O
This H is the symbol for
hydrogen. The little 2
shows that there are 2
hydrogen atoms in the
molecule.
The O is the symbol for
oxygen. Since there is no
number following the O,
we know that there is just
one oxygen atom in the
molecule.
Here’s a simple model of our water molecule:
H
H
O
The States of Matter
When molecules are heated, they become energized and they start to move around.
When they are cooled, the opposite happens. The molecules slow down and clump
together. These behaviors lead to the three main states of matter: solid, liquid and gas.
One easy way to think about these states is to think about the forms of our buddy, H2O.
When it’s cold enough, its molecules group together in
tight crystals to form a solid called ice.
If we warm the ice the molecules start to move around and
break apart forming a liquid that we call water.
If we heat the water enough, the molecules really get active and
they fly out into the air as a gas that we call steam or water
vapor.
One more thing – mixtures and solutions…
When we mix different types of matter together, we form mixtures or solutions, which
are defined by the way that we would break them apart.
¸ A mixture can be taken apart by physical means. Either we can pull out the
different parts, as with a bag of marbles or rocks, or we can use a filter, as with
water and sand.
¸ A solution can’t be taken apart by physical means. An example is salt water. We
can’t pull the salt out by hand, even with a filter. Solutions can be solids, liquids
or gasses.