Particles

Particles

Middle School

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Learning Objectives

• Describe how atoms combine to form molecules and other large extended structures.

• Explain the properties of solids, liquids, and gases based on their particles.

• Explain how thermal energy affects particle motion, temperature, and states of matter.

• Interpret chemical formulas to determine the composition of a pure substance.

• Create models to show the atoms in molecules and extended structures.

Key Vocabulary

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Atom

An atom is the fundamental building block of an element, representing its smallest possible unit.

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Particle

A particle is a general term for a tiny piece of matter, such as an atom or molecule.

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Molecule

A molecule forms when two or more atoms are chemically bonded together to create a single unit.

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Element

An element is a pure substance made of only one type of atom, identified by its atomic number.

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Chemical Formula

A chemical formula uses symbols and numbers to show the types and counts of atoms in a molecule.

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Extended Structure

An extended structure is a large arrangement of atoms or ions formed by repeating subunits, like in crystals.

Key Vocabulary

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Kinetic Energy

Kinetic energy is the energy an object possesses because of its motion.

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Thermal Energy

Thermal energy represents the total kinetic energy of all the particles within a substance.

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Solid

A solid is a state of matter that maintains a fixed shape and volume.

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Liquid

A liquid is a state of matter that has a fixed volume but no fixed shape.

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Gas

A gas is a state of matter with no fixed shape or fixed volume.

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State of Matter

State of matter describes the distinct physical form that matter can exist in, like solid, liquid or gas.

Atoms, Elements, and Particles

• Atoms are the building blocks for all 90 naturally occurring elements.

• An atom is the smallest possible unit of a pure element like gold.

• A particle is the smallest piece of any substance, like an atom or molecule.

Multiple Choice

What is the smallest possible unit of a pure element?

• An atom

• A particle

• An element

• A molecule

Multiple Choice

Which statement best describes the relationship between an atom and a particle?

• An atom is a type of particle.

• A particle is a type of atom.

• Atoms and particles are unrelated.

• Atoms are much larger than particles.

Multiple Choice

If all 90 naturally occurring elements are made of the same fundamental building blocks, what are those blocks called?

• Atoms

• Elements

• Molecules

• Substances

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Molecules and Extended Structures

Simple Molecules

• A molecule consists of a specific number of atoms joined together, like in water, H₂O.

• A chemical formula, such as NH₃ for ammonia, shows the types and number of atoms present.

• Molecules are individual units with a fixed composition and size that exist as distinct particles.

Extended Structures

• An extended structure involves many atoms or ions arranged in a repeating pattern, forming a crystal.

• The chemical formula, like NaCl for salt, shows the simplest ratio of atoms in the structure.

• These structures do not have a fixed size and can grow by adding more repeating units.

Multiple Choice

Which statement best describes a simple molecule?

• It is a distinct particle with a specific number of atoms and a fixed size.

• It is a structure with a repeating pattern of atoms that can grow indefinitely.

• It is a substance whose chemical formula shows the simplest ratio of atoms.

• It is a crystal formed by many different types of molecules joined together.

Multiple Choice

What is the key difference in how a chemical formula represents a simple molecule (like H₂O) versus an extended structure (like NaCl)?

• The formula for a molecule shows the exact number of atoms, while the formula for an extended structure shows the simplest ratio.

• The formula for a molecule uses letters, while the formula for an extended structure uses only numbers.

• The formula for a molecule represents a repeating pattern, while the formula for an extended structure represents a single particle.

• The formula for a molecule can change, while the formula for an extended structure is always fixed.

Multiple Choice

A scientist observes a new material that forms a large crystal. When more atoms are added, the crystal grows larger but maintains the same basic arrangement. How should this material be classified?

• It is an extended structure, because it is formed from a repeating pattern and does not have a fixed size.

• It is a simple molecule, because it is made of a specific number of atoms.

• It is a simple molecule, because all crystals are made of individual molecules.

• It is an extended structure, because it has a chemical formula like H₂O.

States of Matter: Solids

• Particles in a solid are tightly packed in fixed positions.

• They constantly vibrate but do not change their location.

• This fixed arrangement gives solids a definite shape and volume.

Multiple Choice

Which statement best describes the particles that make up a solid?

• They are tightly packed and vibrate in fixed positions.

• They can move freely and slide past one another.

• They are far apart and move in random directions.

• They are in a liquid state and have no definite shape.

Multiple Choice

What is the primary reason solids have a definite shape and volume?

• Because their particles are constantly vibrating.

• Because their particles are locked in a fixed arrangement.

• Because their particles can flow to fit the container.

• Because their particles are very large and heavy.

Multiple Choice

If you could see the individual particles in a block of wood at room temperature, what would you observe?

• The particles would vibrate, but they would remain in their fixed positions.

• The particles would begin to slide past one another.

• The particles would stop moving completely.

• The particles would break apart from each other.

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Properties of Liquids

• Particles in a liquid are close together but can slide past one another.

• Liquids have a definite volume but take the shape of their container.

• The particles move randomly and are constantly colliding with each other.

• This particle movement allows liquids to flow and be poured easily.

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Multiple Choice

Which statement describes a key property of all liquids?

• They have a definite volume and a definite shape.

• They have no definite volume and take the shape of their container.

• They have a definite volume but take the shape of their container.

• Their particles are fixed in place and cannot move.

Multiple Choice

What is it about the particles in a liquid that allows it to flow and be poured?

• The particles are locked in a fixed, rigid structure.

• The particles are very far apart from each other.

• The particles are close but can slide past one another.

• The particles completely stop moving when the liquid is not being poured.

Multiple Choice

If a student carefully pours 100 mL of water from a tall, narrow beaker into a short, wide bowl, what will happen to the water's volume and shape?

• The volume will remain 100 mL, and the shape will change to match the bowl.

• The volume will decrease, and the shape will change to match the bowl.

• The volume will remain 100 mL, and the shape will remain like the beaker.

• The volume will increase to fill the entire bowl.

States of Matter: Gases

• Gas particles are far apart and move randomly and quickly.

• A gas has no fixed shape or volume, filling its container.

• Particle collisions with the container walls create pressure.

Multiple Choice

Which of the following best describes the shape and volume of a gas?

• It has a fixed shape but no fixed volume.

• It has no fixed shape but a fixed volume.

• It has a fixed shape and a fixed volume.

• It has no fixed shape and no fixed volume.

Multiple Choice

What causes a gas to expand and completely fill the container it is in?

• The particles are held tightly in a fixed position.

• The particles create pressure by sticking to the walls.

• The particles move quickly and are far apart from each other.

• The particles are attracted to each other and clump together.

Multiple Choice

If more gas is pumped into a rigid, sealed container, what is the most likely outcome?

• The pressure will decrease because the particles have less room to move.

• The pressure will stay the same because the container's volume has not changed.

• The pressure will increase because of more frequent particle collisions.

• The particles will stop moving because the container is full.

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Energy, Temperature, and Motion

• Kinetic energy is the energy of motion in the particles of a substance.

• Thermal energy is the total kinetic energy of all particles in a substance.

• Temperature measures the average kinetic energy of particles in a substance.

• Heating increases particle motion, which raises the substance's overall temperature.

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Multiple Choice

What does the temperature of a substance measure?

• The total kinetic energy of the particles in the substance.

• The average kinetic energy of the particles in the substance.

• The number of particles in the substance.

• The overall weight of the substance.

Multiple Choice

Which concept explains why a large container of water and a small container of water at the same temperature have different amounts of thermal energy?

• The relationship between thermal energy and temperature.

• The process of particles getting larger when heated.

• The idea that all substances have the same kinetic energy.

• The way particles decrease their motion when heated.

Multiple Choice

If a large pot of soup and a small cup of soup are at the exact same temperature, which statement is the most accurate conclusion?

• The cup of soup has more thermal energy because it is smaller.

• The pot of soup has more thermal energy because it has more particles.

• They have the same thermal energy because they are at the same temperature.

• Their thermal energy cannot be compared without knowing their weight.

Changes in State

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Solid

• Particles are held in fixed positions and vibrate.

• Adding thermal energy can cause the solid to melt into a liquid.

• This change of state is a physical change called melting.

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Liquid

• Particles are close together but are able to move around.

• Adding thermal energy can cause the liquid to boil into a gas.

• Removing thermal energy causes the liquid to freeze into a solid.

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Gas

• Particles are far apart from each other and move very quickly.

• A gas is formed when a liquid is heated to its boiling point.

• Removing thermal energy causes a gas to condense into a liquid.

Multiple Choice

What is the primary factor that causes a substance to change from one state to another?

• The addition or removal of thermal energy

• A change in the substance's mass

• A chemical reaction between particles

• The mixing of two different substances

Multiple Choice

How does the arrangement and motion of particles in a liquid compare to that in a gas?

• Particles in a liquid are in fixed positions, while particles in a gas are close together.

• Particles in a liquid are far apart, while particles in a gas are held in fixed positions.

• Particles in a liquid are close but can move, while particles in a gas are far apart.

• Particles in both liquids and gases are held in fixed positions and only vibrate.

Multiple Choice

On a hot, sunny day, a puddle of water on the sidewalk slowly disappears. Which statement provides the best explanation for this change?

• Lost thermal energy, causing its particles to slow down and freeze into a solid.

• Absorbed thermal energy, causing its particles to move faster and farther apart into a gas.

• Gained mass, causing it to condense and form a new liquid elsewhere.

• Lost its particles to the ground, causing them to become part of the solid surface.

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Common Misconceptions

Misconception	Correction
Heat and temperature are the same thing.	Temperature measures particle energy; heat is the transfer of that energy.
Particles in a solid are completely still.	Particles in a solid are always in motion, vibrating in fixed positions.
If you cut an atom in half, you get two smaller atoms.	An atom is an element's smallest unit; splitting it changes the element.

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Summary

• All matter is made of moving atoms, which form molecules and extended structures.

• A substance can exist as a solid, liquid, or gas depending on particle arrangement.

• Temperature measures the average kinetic energy (energy of motion) of a substance’s particles.

• Adding or removing thermal energy can cause a substance to change its state.

Poll

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

• 1 (Not confident)

• 2 (A little confident)

• 3 (Mostly confident)

• 4 (Very confident)