Composition of Matter
Look around you. A desk, a rock, a jelly doughnut, your finger, and the school
building all have something in common. They are all examples of matter. All
matter, regardless of shape, size, or color, is made up of particles that are too
small to be seen with the human eye. These tiny particles are called atoms and
molecules.
One type of matter is called an element. Scientists have identified over 100
elements on the earth. An element is made up of tiny particles called atoms.
all of the atoms in an element are alike. Gold, for example, is an element made
up only of gold atoms. An aluminum can is made of the element aluminum.
Aluminum is made up only of aluminum atoms.
All atoms have three main parts: protons, neutrons, and electrons. The neutrons
and protons are found in the center of the atom. The center of an atom is called
the nucleus. The electrons circle around the nucleus in the electron cloud.
Another type of matter is called a compound. Most kinds of matter found on
Earth are compounds. A compound is formed when two or more elements join
Together. The smallest particle in a compound is called a molecule. A molecule
Is made up of two or more unlike atoms that are linked together. Water is an
Example of a very important compound on Earth. Water molecules are made up
Of two hydrogen atoms joined with one oxygen atom. Table salt is another
Example of a compound. Salt molecules are made up of one atom of sodium
Joined to one atom of chlorine
States of Matter
We have leaned that everything on Earth is made up of matter. We have also
learned that all matter is made up of tiny particles called atoms. These tiny
particles are always in motion. Matter can be divided into three categories or
states based on how fast or slow these tiny particles are moving. The three
states of matter are solid, liquid, and gas.
In a solid, atoms are packed tightly together and move very slowly. In fact they simply
vibrate back and forth. Because the atoms in a solid barely move, solid matter holds its
shape. Your pencil is an example of solid matter.
In a liquid, the atoms are spaced farther apart and move faster. They are also able to slip
past each other. Because of this, liquids do not hold their shape but take the shape of the
container in which they are placed. The milk you drink at lunch is an example of liquid
matter.
In a gas, the atoms move around very quickly. As they move, they move away from each
other to fill any container they are placed in. Have you ever sprayed air freshener in a
room? Soon the smell fills the entire room and even travels into nearby rooms. This is an
example of how gas atoms travel quickly to fill up an area.
Using this information, can you explain what happens to the movement of atoms when an
ice cube melts?
States of Matter
(continued)
Did you know that changes in temperature can cause matter to change from
one state to another? It’s true! Let’s investigate with water.
Water’s most common state is liquid. In its liquid form, water molecules
move around slowly, sliding past each other. As the temperature drops, the
water molecules gradually slow down. Eventually they stop moving and
simply vibrate back and forth. At this point ice is formed, the solid state of
water.
If the temperature is allowed to increase the molecules will once again
begin to vibrate faster and faster. Eventually they will begin moving and
sliding past one another. At this point the solid state (ice) changes (melts)
back into the liquid state we know as water.
If the temperature continues to rise, the molecules in the liquid begin to
move faster and faster. Eventually they move so fast they change into a
gas and rise into the air.
Using this information, can you explain what happens to a pan full of ice
cubes placed on a hot stove?
Mixture & Solutions
All of the matter around us is made up of mixtures and solutions.
A mixture is formed when two or more different substances are blended
physically. When substances are combined physically, they do not lose their
identifying characteristics.
For example, a handful of coins is a mixture that is blended physically. No
matter how much you mix them around, the pennies are still pennies, the
nickels are still nickels, and the dimes are still dimes. However, the mixtures
are not exactly the same throughout either. For example, the pile of coins in
your hand may have more pennies on the bottom and more nickels and dimes
on top.
Can you think of some more examples of everyday mixtures?
A solution is another kind of mixture. Solutions are formed when one
substance is dissolved in another.
One example of a solution is a glass of sugar water. When you stir sugar into a
glass of water, the sugar dissolves and becomes visible, but it’s still there. In
a solution, the substances are mixed evenly. Solutions are exactly the same
throughout.
Can you think of some more examples of solutions?