Properties and Atoms

Properties and Atoms

Middle School

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Learning Objectives

• Identify the key indicators of a chemical reaction.

• Explain that substances are composed of atoms and molecules.

• Describe how atoms are conserved during a chemical reaction.

• Use models to represent simple molecules and chemical reactions.

Key Vocabulary

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Atom

The smallest unit of an element that maintains the properties of that element.

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Molecule

A group of two or more atoms that are held together by chemical bonds.

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Substance

A type of matter with a fixed composition and a unique set of properties.

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Property

A characteristic of a substance that can be observed, such as its color or odor.

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Chemical Reaction

A process where atoms rearrange to form new substances with different properties.

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Reactant

A substance that is present at the start of a chemical reaction to make products.

Key Vocabulary

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Product

A new substance that is formed as a result of a chemical reaction.

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Model

A representation used to explain something that is too small or large to see.

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Conservation of Mass

The principle that matter is not created or destroyed in a chemical reaction.

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What Are Substances and Properties?

• A substance is matter with a consistent composition and unique properties.

• Scientists use physical and chemical properties to identify different substances.

• Physical properties like boiling point don't change the substance itself.

• Chemical properties like flammability show how a substance can change.

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Multiple Choice

What is the definition of a substance?

• Matter with a consistent composition and unique properties

• Anything that has mass and takes up space

• A material that can easily change its state

• A mixture of different kinds of matter

Multiple Choice

What is the main difference between a physical property and a chemical property?

• Physical properties describe appearance, while chemical properties describe texture.

• Physical properties can be measured, while chemical properties cannot.

• Observing a physical property does not change the substance, while observing a chemical property can.

• Physical properties include boiling point, while chemical properties include melting point.

Multiple Choice

If a piece of wood is burned and turns into ash and smoke, what does this transformation demonstrate?

• A chemical property of the wood

• A physical property of the wood

• The boiling point of the wood

• The consistent composition of the wood

The World of Atoms and Molecules

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Atoms

• All substances are made of tiny particles called atoms.

• Atoms are the basic building blocks of all matter.

• Different types of atoms are known as chemical elements.

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Molecules

• Molecules are made of two or more atoms bonded together.

• A water molecule has two hydrogen and one oxygen atom.

• The chemical formula for the water molecule is H₂O.

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Extended Structures

• These are atoms arranged in a repeating crystal pattern.

• They form large, solid structures instead of separate molecules.

• Examples of these include salt crystals and shiny diamonds.

Multiple Choice

What are the basic building blocks of all matter?

• Atoms

• Molecules

• Salt crystals

• Extended structures

Multiple Choice

What is the primary characteristic that defines a molecule?

• A molecule consists of two or more atoms bonded together.

• A molecule is a single particle of a chemical element.

• A molecule is always arranged in a repeating crystal pattern.

• A molecule is another name for a single atom.

Multiple Choice

A substance is found to be a large, solid material made of atoms arranged in a repeating crystal pattern. Based on this information, what conclusion can be drawn about the substance?

• It is an extended structure.

• It is a collection of separate molecules.

• It is a single, large atom.

• It is a chemical element like oxygen.

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What Are Models of Molecules?

• Scientists use models to study atoms and molecules because they are extremely small.

• Chemical formulas show the type and number of atoms in a single molecule.

• Glucose’s formula, C₆H₁₂O₆, shows 6 carbon, 12 hydrogen, and 6 oxygen atoms.

• Ball-and-stick models use balls for atoms and sticks for the bonds connecting them.

Multiple Choice

What is the primary purpose of using models to represent molecules?

• To understand things that are too small to see.

• To create new types of chemical bonds.

• To change the number of atoms in a molecule.

• To measure the exact size of a molecule.

Multiple Choice

In a ball-and-stick model, what is the relationship between the parts of the model and the molecule it represents?

• The balls represent atoms, and the sticks represent the bonds connecting them.

• The balls represent chemical bonds, and the sticks represent the atoms.

• The balls show the number of molecules, and the sticks show the types of atoms.

• The balls represent the chemical formula, and the sticks represent the 3D shape.

Multiple Choice

The chemical formula for glucose is C₆H₁₂O₆. What must a ball-and-stick model of glucose include to accurately represent this formula?

• Three different types of 'balls' to represent Carbon, Hydrogen, and Oxygen atoms.

• Exactly 6 'balls' and 12 'sticks' in total.

• Only one type of 'ball' because it is a single molecule.

• A total of 24 'sticks' to represent all the atoms.

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What is a Chemical Reaction?

• A chemical reaction transforms one set of chemical substances into another.

• During this process, the atoms of the substances are simply rearranged.

• Starting substances are called reactants, and new substances formed are called products.

• Signs of a reaction include a color change, bubbling, or temperature change.

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Multiple Choice

What is the primary result of a chemical reaction?

• One set of chemical substances is transformed into another.

• Substances are mixed together without changing their properties.

• The atoms of the substances are completely destroyed.

• The temperature of the substances involved always decreases.

Multiple Choice

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

• Reactants are the starting substances whose atoms are rearranged to form products.

• Products are the starting substances that combine to form reactants.

• Reactants and products are different names for the same substances.

• Reactants are the signs of a reaction, while products are the starting materials.

Multiple Choice

If you mix two substances and observe that the container gets warmer and the color changes, what can you conclude?

• A chemical reaction has likely occurred.

• The two substances have simply mixed together.

• The experiment failed because no bubbling was observed.

• The starting substances were destroyed in the process.

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What Is the Law of Conservation of Mass?

• Mass is never created or destroyed during any chemical reaction.

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

• In a reaction, atoms are only rearranged to form new substances.

• No atoms are ever lost, and no new atoms are ever created.

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Multiple Choice

Which statement best defines the law of conservation of mass?

• Mass is only important in physical changes.

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

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

• New atoms are created during chemical reactions.

Multiple Choice

How can the total mass remain the same during a chemical reaction?

• Some atoms in the reactants are destroyed.

• New atoms are created to form the products.

• The atoms of the reactants are rearranged to form the products.

• The number of atoms increases during the reaction.

Multiple Choice

If a chemical reaction starts with 50 grams of reactants in a sealed container, what must be true about the mass of the products?

• The total mass of the products will be less than 50 grams.

• The total mass of the products will be greater than 50 grams.

• The total mass of the products will be exactly 50 grams.

• It is impossible to predict the mass of the products.

Energy in Chemical Reactions

• Chemical reactions involve energy changes, often as heat.

• Exothermic reactions release energy, making the surroundings warmer.

• Endothermic reactions absorb energy, making the surroundings colder.

Multiple Choice

What is a fundamental characteristic of chemical reactions regarding energy?

• They always create a new solid substance.

• They always involve a change in energy.

• They always require a source of light.

• They always produce a noticeable smell.

Multiple Choice

What is the primary difference between exothermic and endothermic reactions?

• Exothermic reactions create heat, while endothermic reactions create cold.

• Exothermic reactions happen quickly, while endothermic reactions happen slowly.

• Exothermic reactions release energy, while endothermic reactions absorb it.

• Exothermic reactions require energy, while endothermic reactions produce it.

Multiple Choice

If a chemical reaction in a beaker causes the beaker to feel cold to the touch, what is the best explanation for this?

• The reaction is exothermic because it is releasing cold energy.

• The reaction is endothermic because it is absorbing heat from its surroundings.

• The reaction is exothermic because it is destroying heat in the beaker.

• The reaction is endothermic because it is creating a new cold substance.

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Synthetic Materials from Natural Resources

• Many materials we use are synthetic, meaning they are human-made.

• These materials are made from natural resources found in our environment.

• For example, crude oil is a natural resource used to make plastics.

• This process provides useful items but can also cause pollution.

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Multiple Choice

Which statement best defines a synthetic material?

• It is a material made by humans using natural resources.

• It is a material that occurs naturally in the environment.

• It is a material that is always biodegradable.

• It is a material that is only used for fuel.

Multiple Choice

What is the relationship between crude oil and plastic?

• Crude oil is a natural resource that is used to create the synthetic material plastic.

• Plastic is a natural resource that is used to create the synthetic material crude oil.

• They are both synthetic materials created by humans.

• They are both natural resources found underground.

Multiple Choice

What conclusion is best supported by the information about making synthetic materials?

• The production of useful items from natural resources can also lead to environmental harm.

• The use of synthetic materials has no negative consequences.

• All natural resources are primarily used to make plastics.

• Pollution is only caused by the use of natural resources, not synthetic ones.

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Common Misconceptions

Misconception	Correction
Chemical reactions always involve explosions or bubbling.	Many reactions are silent and slow, like rusting.
Atoms are created or destroyed in a reaction.	Atoms are only rearranged to form new molecules.
Physical changes are the same as chemical reactions.	In a physical change, molecules don't change (ice is still H2O).
You can turn any substance into any other substance.	You can only form products that use atoms from the reactants.

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Summary

• All substances are made of atoms and have unique properties.

• Chemical reactions rearrange atoms to form new substances with different properties.

• Mass is conserved in reactions, which can release or absorb energy.

• Synthetic materials are made from natural resources using chemical reactions.

Open Ended

In your own words, explain the difference between a physical change (like tearing paper) and a chemical change (like burning paper).

Poll

A new energy drink powder is mixed with water and the bottle becomes very cold. What type of reaction is this?

• Exothermic

• Endothermic

• Physical Change

• No Reaction

Poll

On a scale of 1-4, how confident are you about explaining the Law of Conservation of Mass to a friend?

• 1 - Not confident at all

• 2 - A little confident

• 3 - Mostly confident

• 4 - Very confident