Matter's Properties and Changes

Matter's Properties and Changes

Middle School

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Learning Objectives

• Define properties of matter at the macroscopic and atomic levels.

• Use properties like density to identify substances and determine if a reaction occurred.

• Use a model to describe how atoms are conserved in a chemical reaction.

• Describe how synthetic materials are made from natural resources through chemical processes.

• Compare endothermic and exothermic reactions based on whether they absorb or release energy.

Key Vocabulary

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Atom

Smallest particle of an element that retains the element's chemical identity in reactions.

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Molecule

Two or more atoms linked by chemical bonds acting as a single neutral particle.

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Extended Structure

Large arrangement of repeating subunits, such as crystals or polymers, forming solid materials.

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Physical Property

Characteristic measured or observed without changing substance composition, like color, density, or melting point.

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Chemical Property

Characteristic that becomes evident during chemical change, such as flammability or ability to rust.

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Density

Key Vocabulary

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Chemical Reaction

A chemical reaction is a process that involves the rearrangement of atoms to create entirely new substances.

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Reactant

A reactant is a substance that you start with before a chemical reaction begins.

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Product

A product is a new substance that is formed at the end of a chemical reaction.

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Conservation of Mass

The law of conservation of mass states that mass is never created or destroyed in reactions.

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Endothermic Reaction

An endothermic reaction is a chemical process that absorbs, or takes in, thermal energy from its surroundings.

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Exothermic Reaction

An exothermic reaction is a chemical process that releases thermal energy, often in the form of heat.

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Physical Properties: Mass and Volume

Mass

• Mass is the amount of matter in an object, which is commonly measured in grams (g).

• It is a size-dependent property, as a larger object will have more mass than a smaller one.

• It is different from weight, which is the measure of the pull of gravity on an object.

Volume

• Volume is the amount of space an object occupies, measured in cubic centimeters (cm³).

• Volume is also a size-dependent property because a larger object takes up more space than a smaller one.

• An irregularly shaped object's volume can be found by using the water displacement method.

Multiple Choice

Which statement correctly defines mass and volume?

• Mass is the space an object occupies, and volume is the matter it contains.

• Mass is the amount of matter in an object, and volume is the amount of space it occupies.

• Mass is the pull of gravity on an object, and volume is its physical size.

• Mass and volume are both the amount of matter in an object.

Multiple Choice

Why are both mass and volume described as size-dependent properties?

• Because they are both measured using metric units like grams and centimeters.

• Because a larger object generally contains more matter and takes up more space.

• Because both properties can be measured using the water displacement method.

• Because they are different from weight, which changes depending on gravity.

Multiple Choice

A student needs to find the volume of a small, irregularly shaped stone. Which of the following describes the correct scientific method?

• Place the stone on a scale to determine the pull of gravity on it.

• Measure the length, width, and height of the stone with a ruler.

• Place the stone in a measuring cup with water and measure the change in the water level.

• Compare the stone to a larger object to see which one has more matter.

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Physical Properties: Density

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Multiple Choice

Which statement best defines density?

• The amount of mass in a specific volume

• The total weight of an object

• The amount of space an object occupies

• The shape and texture of a substance

Multiple Choice

If you cut a large block of wood into two smaller pieces, how does the density of one small piece compare to the original large block?

• The density of the large piece is greater.

• The density of the small piece is greater.

• The density of both pieces is the same.

• The density depends on the shape of the pieces.

Multiple Choice

An object has a mass of 30 g and a volume of 40 cm³. If placed in water (density = 1 g/cm³), what will most likely happen?

• It will sink because its mass is 30 grams.

• It will float because its volume is 40 cm³.

• It will sink because its density is greater than water.

• It will float because its density is less than water.

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Chemical and Other Identifying Properties

• A chemical property describes matter’s ability to change into a new substance.

• Observing a chemical property requires a chemical reaction.

• Key chemical properties include: flammability (burns in air), reactivity (reaction with acids or oxygen), and ability to rust or oxidize.

• Examples:

  • Hydrogen + oxygen → water (reactivity)

  • Wood catching fire (flammability)

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Multiple Choice

Which statement best defines a chemical property?

• It describes matter’s ability to change into a new substance.

• It is a characteristic that can be seen without changing the substance.

• It relates to the size, shape, or state of matter.

• It is the temperature at which a substance melts or freezes.

Multiple Choice

What is required to observe an identifying property like flammability?

• A chemical reaction must occur to observe how the substance changes.

• The substance must be measured using a ruler or scale.

• The substance must be observed at a distance without touching it.

• The color and texture of the substance must be recorded.

Multiple Choice

A scientist observes that a piece of iron begins to rust when it is exposed to oxygen in the air. Which chemical property is being demonstrated?

• Reactivity

• Solubility

• Boiling point

• Odor

Atomic Composition of Matter

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Atoms

• All substances are made from different types of tiny particles called atoms.

• Atoms are the fundamental building blocks of all matter around us.

• They are so small that we cannot see them directly.

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Molecules

• Molecules form when two or more atoms chemically bond together.

• A water molecule, H₂O, has two hydrogen atoms and one oxygen atom.

• Molecules are the smallest unit of many familiar substances like water.

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Extended Structures

• Some substances form large, repeating patterns of atoms or ions.

• This repeating arrangement is called a crystal lattice, like in table salt.

• Sodium chloride, NaCl, is a common example of a crystal lattice.

Multiple Choice

What are the fundamental building blocks of all matter?

• Molecules

• Atoms

• Extended structures

• Crystal lattices

Multiple Choice

What is the relationship between an atom and a molecule?

• A molecule is a repeating pattern, while an atom is not.

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

• An atom is the smallest unit of water, while a molecule is not.

• An atom is visible, but a molecule is too small to be seen.

Multiple Choice

If a substance is described as a large, repeating pattern of bonded atoms, such as in table salt, how should it be classified?

• As a molecule like H₂O

• As an extended structure

• As a single, fundamental atom

• As a collection of unbonded atoms

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Chemical Reactions and Conservation of Mass

• A chemical reaction rearranges atoms from reactants to form new products.

• The Law of Conservation of Mass states that mass is always conserved.

• Atoms are simply rearranged during a reaction, not created or destroyed.

• For example, 2H₂ + O₂ → 2H₂O shows atoms regrouping to form water.

Multiple Choice

Which statement best describes the Law of Conservation of Mass?

• Atoms are conserved and are not created or destroyed.

• New atoms are created to form the products.

• Some atoms are lost during the reaction.

• Atoms change into different types of atoms.

Multiple Choice

According to the Law of Conservation of Mass, how can a chemical reaction result in new products without losing any atoms?

• By rearranging the existing atoms of the reactants.

• By adding new atoms from the surrounding air.

• By changing the type of atoms involved.

• By breaking down atoms into smaller particles.

Multiple Choice

A chemical reaction begins with reactants containing 4 hydrogen (H) atoms and 2 oxygen (O) atoms. After the reaction is complete, what must be true about the atoms in the products?

• The products must contain exactly 4 hydrogen atoms and 2 oxygen atoms.

• The products will contain more atoms than the reactants.

• The products will be made of different types of atoms.

• The products must have fewer than 6 atoms in total.

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Energy in Chemical Reactions

Exothermic Reactions

• These reactions release more energy than they absorb, releasing energy into the surroundings.

• The release of energy, often as heat, causes the temperature of the surroundings to rise.

• The general equation for this reaction is: reactants → products + energy.

Endothermic Reactions

• These reactions absorb more energy than they release, taking energy from the surroundings.

• This absorption of energy causes the temperature of the surroundings to drop.

• The general equation for this reaction is: reactants + energy → products.

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Synthetic Materials from Natural Resources

• Synthetic materials are made by people through chemical processes.

• These processes turn natural resources into new, useful materials.

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

• They are used for medical devices, clothing, and other products.

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Multiple Choice

What is the defining characteristic of a synthetic material?

• It is found growing in nature.

• It is created by people using chemical processes.

• It is a raw material taken from the Earth.

• It is a type of plant or animal.

Multiple Choice

What is the relationship between natural resources and synthetic materials?

• Synthetic materials are used to create natural resources.

• Natural resources are a type of synthetic material.

• Natural resources and synthetic materials are the same thing.

• Natural resources are chemically changed to form synthetic materials.

Multiple Choice

If scientists wanted to develop a new synthetic material to make waterproof clothing, what would their process most likely involve?

• Find a natural resource that can be chemically changed to have the desired properties.

• Search for a plant that already repels water.

• Mix several types of existing clothing together.

• Use petroleum to make medical devices instead.

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Common Misconceptions

Misconception	Correction
When a substance dissolves or burns, its mass is destroyed.	Mass is conserved; atoms are just rearranged to form new substances.
Atoms are changed into new types of atoms during a reaction.	Atoms are only rearranged into new combinations; they do not change identity.
Synthetic materials are completely “unnatural.”	All synthetic materials originate from natural resources that are chemically altered.
Exothermic reactions create energy from nothing.	Energy is conserved; it is released from the chemical bonds of reactants.

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Summary

Poll

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

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