Name:______Date:______Period: _____
Unit 8: Matter and Temperature
Section 3: Phases of Matter
Learning Goals
· Identify the phases of matter.
· Describe the behavior of atoms and molecules as matter undergoes phase changes.
· Describe properties of plasmas.
Phases of Matter
On Earth, pure substances are usually found as solids, liquids, or gases. These are called phases of matter.
1. Solids
A solid holds its shape and does not flow. The molecules in a solid vibrate in place, but on average, don’t move far from their places.
2. Liquids
A liquid holds its volume, but does not hold its shape—it flows. Liquids flow because the molecules can move around.
3. Gases
A gas flows like a liquid, but can also expand or contract to fill a container. A gas does not hold its volume. The molecules in a gas have enough energy to completely break away from each other.
4. Plasma
In the plasma phase, matter becomes ionized as electrons are broken loose from atoms.
The Sun is made of plasma, as is most of the universe, including the Orion nebula. However, plasma is not as common on Earth so it is not always included in the phases of matter.
Besides super-heating a substance to 10,000˚C, there are other ways of creating plasma. If you pass an electrical current through a gas, like neon for example, the electrons are stripped off and you get plasma at manageable temperatures.
Intermolecular Forces
When they are close together, molecules are attracted through intermolecular forces.
The forces in chemical bonds are stronger than intermolecular forces.
For example: It is easier to break the intermolecular bonds in ice by simply letting it melt, but it is difficult to separate the hydrogen from the oxygen in the water molecule because that bond is much stronger.
Within all matter, there is a constant competition between temperature (resulting from the vibrations of matter) and intermolecular forces (the forces trying to hold everything together).
· When temperature wins the competition, molecules fly apart and you have a gas.
· When intermolecular forces win the competition, molecules clump tightly together and you have a solid.
Melting and Boiling Points
The melting point is the temperature at which a substance changes from a solid to a liquid. Water melts at or above 32˚ F or 0˚ C.
The temperature at which a liquid becomes a gas is called the boiling point. Water boils at or above 212˚ F or 100˚ C.
Materials have a wide range of melting and boiling points because the intermolecular forces vary in strength.
Sublimation
Sometimes a solid can change directly to a gas when heat energy is added. This process is called sublimation.
Vocabulary
solid – a phase of matter that holds its shape and does not flow.
liquid – a phase of matter that holds its volume, does not hold its shape, and flows.
gas – a phase of matter that flows, does not hold its volume, and can expand or contract to fill a container.
intermolecular forces – forces between atoms or molecules in a substance that determine the phase of matter.
melting point – the temperature at which a substance changes from solid to liquid (melting) or liquid to solid (freezing).
boiling point – the temperature at which a substance changes from liquid to gas (boiling) or from gas to liquid (condensation).
plasma – a phase of matter in which the matter is heated to such a high temperature that some of the atoms begin to break apart.
Review Questions
1. What are the four phases of matter that are possible? (start with the lowest temperature phase and end with the highest)
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2. For each of the properties described below, label which common phase or phases have that property.
a. Molecules do not move around, but vibrate in place. ______
b. Has volume, but no particular shape. ______
c. Flows ______
d. Molecules break free of intermolecular forces. ______
e. Does not have a volume or shape. ______
f. Molecules can move around and switch places, but remain close together.______
3. Label the following examples as either solid, liquid, gas, or plasma.
a. blood ______c. solar flare ______
b. helium ______d. wood ______
4. Which would you expect to have higher intermolecular forces? Why?
a. Hydrogen, which exists as a gas at room temperature.
b. Iron, a metal which exists as a solid at room temperature.
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5. Which is stronger: intermolecular bonds or chemical bonds? ______
6. Materials have a wide range of melting and boiling points because the intermolecular forces vary in ______.
7. When a solid changes directly into a gas it is called ______.
8. Man-made plasma is created when an electrical current is passed through a ______, such as ______. (example)
Complete the chart about the phases of matter using the information in your notes and in the text.
Solid / Molecules vibrate in place; do not move / Holds shape and doesn’t flow / lowest / strong
Liquid / Molecules move around / Holds its volume, doesn’t hold shape / low / weak
Gas / Molecules break away and are much farther apart than in a liquid or solid / Expands or contracts to fill container / high / weakest
Plasma / Atoms break apart / No definite volume or shape / highest / none
In the boxes provided below, draw a representation of what the molecules look like in each of the phases of matter.
Solid / Liquid / Gas / PlasmaPage 11