Chemical Interactions

Chemical Interactions

Middle School

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Learning Objectives

• Define atoms, elements, molecules, and compounds, and differentiate between bond types.

• Use data to determine if a chemical reaction has occurred.

• Explain how mass is conserved and energy changes in chemical reactions.

• Describe how synthetic materials are made from natural resources.

Key Vocabulary

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Atom

The atom is the basic building block of a chemical element.

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Element

An element is a pure substance that consists of only one type of atom.

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Molecule

A molecule is a group of two or more atoms held together by chemical bonds.

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Compound

A compound is a substance formed when different elements are chemically bonded together.

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Ionic Bond

An ionic bond is a chemical bond that forms from the transfer of electrons between atoms.

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Covalent Bond

A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms.

Key Vocabulary

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Chemical Reaction

This is a process where atoms in reactants rearrange to form new substances, which are called the products.

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Reactant

A reactant is a substance that is present at the beginning of a chemical reaction and gets consumed.

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Product

A product is a new substance that is formed as the result of a chemical reaction taking place.

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Exothermic Reaction

This is a type of chemical reaction that releases energy into the surroundings, usually as heat or light.

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Endothermic Reaction

An endothermic reaction is a chemical process that absorbs energy from its surroundings, often in the form of heat.

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Synthetic Material

A synthetic material is a material made by humans through chemical processes; it is not found in nature.

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Atoms, Elements, and Molecules

• All matter is made of atoms, the basic building blocks of an element.

• An element is a pure substance that consists of only one type of atom.

• When atoms bond, they form a molecule, like an oxygen molecule (O₂).

• A compound is a molecule made of different elements, like carbon dioxide (CO₂).

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Multiple Choice

What is the basic building block of an element?

• An atom

• A compound

• A molecule

• A substance

Multiple Choice

What is the key difference between an element and a compound?

• An element consists of one type of atom, while a compound consists of different types of atoms.

• An element is always a solid, while a compound is always a gas.

• An element is a mixture, while a compound is a pure substance.

• An element cannot form bonds, while a compound can.

Multiple Choice

An oxygen molecule (O₂) contains only oxygen atoms, while a carbon dioxide molecule (CO₂) contains carbon and oxygen atoms. Which conclusion can be drawn from this information?

• Carbon dioxide is a compound, while oxygen is not.

• Oxygen is a compound, while carbon dioxide is not.

• Both oxygen and carbon dioxide are elements.

• Neither oxygen nor carbon dioxide are molecules.

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Chemical Bonds: Ionic vs. Covalent

Ionic Bonds

• One atom transfers one or more electrons to another atom.

• This transfer creates charged particles called ions that attract one another.

• A common example is Sodium Chloride (NaCl), which forms table salt.

Covalent Bonds

• Atoms share one or more pairs of electrons with each other.

• The atoms cooperate to complete their outer electron shells.

• A classic example is water (H₂O), made of hydrogen and oxygen atoms.

Multiple Choice

What is the defining characteristic of an ionic bond?

• One atom transfers one or more electrons to another atom.

• Atoms share one or more pairs of electrons with each other.

• Atoms cooperate to form a new type of element.

• Atoms break apart into smaller particles.

Multiple Choice

How does the formation of an ionic bond differ from the formation of a covalent bond?

• Ionic bonds create charged particles, while covalent bonds create new atoms.

• Ionic bonds involve the transfer of electrons, while covalent bonds involve the sharing of electrons.

• Ionic bonds form water, while covalent bonds form table salt.

• Ionic bonds only happen with metals, while covalent bonds only happen with nonmetals.

Multiple Choice

Two atoms are near each other and complete their outer electron shells by sharing a pair of electrons. What is the most likely outcome?

• The atoms will form an ionic bond by creating charged particles.

• The atoms will form a covalent bond, like in a water molecule.

• One atom will become table salt, and the other will become water.

• The atoms will repel each other and not form a bond.

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Chemical Reactions and Equations

• A chemical reaction is a process that rearranges atoms to create new substances.

• The starting substances are reactants, and the new substances formed are products.

• A chemical equation represents this, like 2H₂ + O₂ → 2H₂O.

• Signs of a reaction include a change in color, temperature, or gas formation.

Multiple Choice

What happens during a chemical reaction?

• Atoms are rearranged to create new substances.

• Substances are mixed together without changing.

• Substances change their state, like melting or freezing.

• Atoms are destroyed and new ones are created.

Multiple Choice

What is the relationship between reactants and products in a chemical reaction?

• Reactants are the starting substances, and products are the new substances formed.

• Reactants and products are both present at the beginning of a reaction.

• Reactants are the substances formed, and products are the starting substances.

• Reactants and products are always the same chemical substance.

Multiple Choice

If you mix two clear liquids and observe that the mixture begins to bubble and feels warmer, what can you conclude?

• A chemical reaction has occurred.

• The liquids have simply been stirred together.

• One of the liquids has evaporated quickly.

• The substances have dissolved into each other.

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Identifying Chemical Reactions by Properties

• A chemical reaction creates new substances with different properties.

• We can measure properties before and after to identify a chemical reaction.

• Key properties include density, melting point, boiling point, solubility, and flammability.

• For example, flammable wood burns to create ash, which is not flammable.

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Multiple Choice

What is the primary result of a chemical reaction?

• New substances with different properties are formed.

• Substances change their state, like melting or freezing.

• Substances are physically mixed together without changing.

• The original substances are separated into their components.

Multiple Choice

How can scientists determine that a chemical reaction has created a new substance?

• By measuring and comparing properties like density or flammability before and after.

• By observing if the substance has changed color or shape.

• By checking if the total mass of the substances has increased.

• By seeing if the substances can be easily mixed together.

Multiple Choice

A substance is tested and found to have a melting point of 0^oC. After it is mixed with another substance, the resulting material has a melting point of -5^oC. What is the best conclusion from this observation?

• A chemical reaction occurred, creating a new substance.

• The original substance only dissolved, it did not react.

• The temperature of the room must have changed.

• The measurement is likely incorrect because properties cannot change.

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The Law of Conservation of Mass

• Mass is not created or destroyed during a chemical reaction, it is conserved.

• ​The number and types of atoms are the same before and after a reaction.

• Atoms are rearranged to form new molecules, but they are never lost or gained.

• The total mass of reactants equals the total mass of the products.

Multiple Choice

What is the fundamental principle of the Law of Conservation of Mass?

• Mass is never created or destroyed in a chemical reaction.

• The mass of products is always greater than the reactants.

• Atoms change their type during a chemical reaction.

• The number of atoms changes during a chemical reaction.

Multiple Choice

Why does the total mass remain the same during a chemical reaction?

• The atoms are not created or destroyed, only rearranged.

• The reactants lose mass when they turn into products.

• New atoms are formed, but they have the same mass.

• Energy is converted into mass during the reaction.

Multiple Choice

If 24 grams of magnesium (a reactant) completely react with 88 grams of oxygen (another reactant), what can you conclude about the mass of the product formed?

• The total mass of the products will be 112 grams.

• The total mass of the products will be 88 grams.

• The total mass of the products will be less than 112 grams.

• It is impossible to know the mass without seeing the reaction.

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Energy in Chemical Reactions

Exothermic Reactions

• Reactions that release thermal energy into their surroundings.

• This release of energy causes the surroundings to feel warmer.

• Burning wood and hand warmers are common examples of these reactions.

Endothermic Reactions

• Reactions that absorb thermal energy from their surroundings.

• This absorption of energy causes the surroundings to feel colder.

• The chemical reaction inside an instant cold pack is an example.

Multiple Choice

What is the fundamental difference between an exothermic and an endothermic reaction?

• By whether the reaction releases or absorbs energy.

• By the color of the substances involved.

• By how long the reaction takes to complete.

• By whether the reaction produces a gas or a solid.

Multiple Choice

What is the direct cause for the area around a burning campfire to feel warmer?

• The reaction absorbs cold from the environment.

• The reaction releases thermal energy into its surroundings.

• The reaction creates a barrier that traps heat.

• The reaction consumes the oxygen in the air.

Multiple Choice

If a student mixes two chemicals and observes that the beaker containing them becomes cold to the touch, what conclusion can be drawn?

• An exothermic reaction is occurring, releasing cold into the beaker.

• An endothermic reaction is occurring, absorbing heat from its surroundings.

• The liquids were simply cold to begin with.

• The glass of the beaker is preventing heat from escaping.

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Synthetic Materials From Natural Resources

• Synthetic materials are made by humans using chemical processes.

• They are not found in their final form in nature.

• Natural resources are changed by chemical reactions to create them.

• For example, plastics are made from petroleum, a natural resource.

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Multiple Choice

Which statement best defines a synthetic material?

• A material made by humans using chemical processes.

• A material found in its final form in the natural world.

• A raw material extracted directly from the Earth.

• A material that exists without any human changes.

Multiple Choice

What is the relationship between natural resources and synthetic materials?

• Natural resources and synthetic materials are the same.

• Synthetic materials are used to create natural resources.

• Natural resources are chemically changed to create synthetic materials.

• Synthetic materials are simply natural resources found in different places.

Multiple Choice

Plastic is a synthetic material made from petroleum, which is a natural resource. What does this example suggest about the process of creating synthetic materials?

• The chemical process changes petroleum into a new substance with different properties.

• Plastic is a natural resource found alongside petroleum.

• Petroleum is a synthetic material made from plastic.

• The process involves physically mixing petroleum with other natural materials.

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Common Misconceptions

Misconception	Correction
Atoms are created or destroyed in chemical reactions.	Atoms are only rearranged; they are not created or destroyed.
Mixing substances always causes a chemical reaction.	A chemical reaction only occurs if new substances are formed.
Bubbles always mean a chemical reaction is happening.	Bubbles can also be from boiling, which is a physical change.
All chemical reactions produce heat.	Some reactions release heat (exothermic), while others absorb it (endothermic).

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Summary

• Atoms bond to form molecules, and chemical reactions rearrange these atoms into new products.

• Reactions are signaled by property changes and can release or absorb energy.

• The Law of Conservation of Mass states that atoms are conserved in reactions.

• Chemical processes create useful synthetic materials from natural resources.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1 (Not confident at all)

• 2 (A little confident)

• 3 (Mostly confident)

• 4 (Very confident)