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8th Grade Science
Midterm Exam Key Concepts
Scientific Inquiry
1. Understanding Science
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Lab safety is an important concern for scientists.
A balance measures mass, and a thermometer measures temperature.
2. Scientific Theory and Scientific Law
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A scientific law states that something will happen every time.
If a hypothesis is not supported, a scientist should modify and revise the hypothesis
first.
The variable changed in an experiment is the independent variable.
A controlled experiment usually has two groups: a control group and an experimental
group.
Foundations of Chemistry
1. Classifying Matter
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A homogeneous mixture is evenly dissolved, while a heterogeneous mixture has
visible particles and can settle out.
Solution is another name for a homogeneous mixture.
When two substances are combined so that they can be separated by physical means,
the result is a mixture.
2. Physical Properties
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Some physical properties of matter are color, shape, and size.
3. Physical Changes
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Some examples of physical changes are freezing, melting, cutting grass, and carving a
statue.
When an object goes through a physical change, it is still the same substance after the
change.
4. Chemical Properties and Changes
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Some chemical properties are flammability and reactivity.
Examples of a chemical change include burning wood and rusting.
When an object goes through a chemical change, new substance are ALWAYS
formed.
States of Matter
1. Solids, Liquids, and Gases
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The four most common states of matter are solids, liquids, gases, and plasma.
The three states of water are ice, liquid water, and water vapor.
Viscosity is a measure of a liquid’s resistance to flow.
2. Changes in State
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As temperature increases, particle motion increases.
Kinetic energy is energy of motion.
Thermal energy is the sum of an object’s potential energy and kinetic energy.
Temperature is the measure of the average kinetic energy of a substance.
A change in a state of matter happens if enough thermal energy is added or removed.
Changes from: solid to liquid = melting; liquid to gas = vaporization; solid to gas =
sublimation; gas to solid = deposition; gas to liquid = condensation; liquid to solid =
freezing
3. The Behavior of Gases
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An example of Charles’s law in action is a hot air balloon rising more easily in cooler
weather than warmer weather.
Boyle’s law describes the properties of a gas.
Atoms and the Periodic Table
1. Protons, Neutrons, and Electrons – How Atoms Differ
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The three parts of an atom are protons, neutrons, and electrons.
The nucleus of an atom consists of protons and neutrons.
Protons are positive, electrons are negative, and neutrons are neutral.
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For an atom to be neutral, the number of protons must equal the number of
electrons.
2. Using the Periodic Table
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A horizontal row on a periodic table is called a period.
In the modern periodic table, elements are arranged according to atomic number.
You can determine mass number by adding protons and neutrons together.
An element can be identified from the number of protons in its nucleus.
3. Metals
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Three-fourths of the periodic table is metals.
At room temperature, most metal are solids.
4. Nonmetals and Metalloids
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Metalloids have properties of both metals and nonmetals.
Helium and most nonmetals are found on the right side of the periodic table.
Chemical Reactions and Equations
1. Understanding Chemical Reactions
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When an equation has the same number of atoms on both sides, it is balanced.
In a chemical equation, the formulas to the left of the arrow are the reactants, and the
formulas to the right of the arrow are the products.
2. Types of Chemical Reactions
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The main types of chemical reactions are synthesis, decomposition, singlereplacement, and double-replacement.
3. Energy Changes and Chemical Reactions
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Energy is needed to break bonds in chemical reactions.
An endothermic reaction absorbs energy and an exothermic reaction releases energy.