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Key Question #1: How are changes in the matter that makes up living and nonliving things similar?
Atoms are rearranged to form new molecules and substances in both living and nonliving things.
Key Question #2: How do we know if a different substance has been made?
A new substance is made if the substance exhibits different properties than the original substance.
Science Idea #1
Every substance has a unique set of characteristic properties, such as color, odor, density, melting point, conductivity and solubility, and how it behaves (such as in limewater and glowing splint tests). The properties of substances can be observed or measured and used to decide if two substances are the same or different.
Evidence: Oxygen gas and carbon dioxide are different substances because they have different properties. Oxygen has a melting point of -219 degrees Celsius while carbon dioxide melts at -78 degrees Celsius. The density of oxygen is 0.001 gram per cubic centimeter and the density of carbon dioxide is 0.003 gram per cubic centimeter.
Key Question #3: As a new substance forms, what happens to the starting substances?
As more and more new substances are formed, the amount of the starting substance decreases.
Science Idea #2
Changes during which new substances form are called chemical reactions. The correlation of increasing amounts of ending substances with decreasing amounts of the starting substances provides evidence that the new substances result from an interaction between the starting substances.
Evidence: When nylon is pulled out of hexamethylenediamine and adipic acid, the amount of nylon increases while the amount of the reactants decreases. Water and nylon are the new substances formed.
Key Question #4: Why do the substances produced in a chemical reaction have different properties from the starting substances?
The substances produced in a chemical reaction has different properties because the atoms are rearranged. A different arrangement of atoms determines the properties of the substance.
Science Idea #3
A molecule is made up of two or more atoms connected together in a specific arrangement.
Evidence: A carbon dioxide molecule is made of one carbon atom and two oxygen atoms. Acetic acid is made up of four hydrogen atoms, two carbon atoms, and two oxygen atoms.
Science Idea #4
Each substance is made up of a single type of atom or molecule. The properties of a substance are determined by the type, number, and arrangement of atoms that it is made up of. Because no two substances are made up of the same arrangement of atoms, no two substances have the same set of properties.
Evidence: Carbon dioxide is composed of different atoms with a different arrangement than oxygen and water. They have different properties because they have a different arrangement of atoms.
Key Question #5: How are the molecules of the ending substances made?
The molecules of the ending substances are made when the atoms of the molecules of the starting substances rearrange and form new bonds.
Science Idea #5
During chemical reactions, atoms that make up molecules of the starting substances (called reactants) disconnect from one another and connect in different ways to form the molecules of the ending substances (called products). Because the arrangement of atoms in the products is different from the arrangement of atoms in the reactants, the products of a chemical reaction have different properties from the reactants.
Evidence: When iron and oxygen reacts, the atoms rearrange and form new bonds to produce rust. 4Fe+3O2 ---> 2Fe2O2. The oxygen atoms form bonds with the iron atoms to make rust, which exhibits different properties than iron and oxygen.
Key Question #6: How can small molecules be used to make very large molecules?
Small molecules can bond together to form very large molecules. Monomers can bond in two different places to form large polymers.
Science Idea #6
Very large molecules called polymers can be formed by reacting small molecules (monomers) together. Because monomers can react in two places, it is possible for each monomer to react with two other monomers to form long polymer chains. Each time a monomer is added to the chain, atoms are rearranged and another molecule, typically water, is formed.
Evidence: Para-phenylenediamine and terephthaloyl chloride monomers bond together to form Kevlar polymers.
Key Question #7: What happens to the amount of matter (mass) when new substances form during chemical reactions?
The mass is conserved because the amount of starting substances decrease and the amount of ending substances increases. Mass is conserved because no new atoms are created and no atoms are destroyed.
Key Question #8: Why does rearranging atoms keep the total mass constant during chemical reactions?
The number of atoms does not decrease or increase during chemical reactions so the total mass is constant.
Science Idea #7
Atoms are not created or destroyed during chemical reactions, so the total number of each type of atom remains the same. We say that atoms are conserved.
Evidence: Balanced chemical equations
Science Idea #8
The mass of a particular atom does not change, so a given number of that type of atom will always have the same total mass.
Evidence: 4 iron atoms plus 6 oxygen atoms will have the same mass no matter how the atoms are arranged
Science Idea #9
Because the mass of a particular atom does not change and because the number of each type of atom stays the same, the total mass of the matter stays the same even though atoms are rearranged during chemical reactions.
Evidence: mass is conserved.
Key Question #9: If atoms and total mass are always conserved during chemical reactions, why can measured mass change when the container is opened?
Measured mass may change when containers are opened because atoms can leave the container and new atoms can enter and bond with existing atoms, lowering or increasing the measured mass.
Science Idea #10
The measured mass of reactants and products is not always the same as the total mass. The measured mass changes if reactants or products (often gases) enter or leave the system. This is because atoms that make up reactants or products enter or leave the system.
Evidence: In a chemical reaction between baking soda and vinegar, the initial mass was 986.7 grams. After the chemical reaction, the mass was also 986.7 grams. When the container was opened, the mass decreased because molecules (carbon dioxide) exited the container into the air around the container. In a reaction between iron and oxygen, both the initial mass and the final mass was 139.03 grams. After the container was opened, the mass increased to 141.79 grams because oxygen atoms entered and formed bonds with the iron atoms to create rust.