States of matter and particle motion

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Lesson notes

Particle Model of Matter

All matter is made of tiny **particles** (atoms, molecules, or ions) that are in constant motion.
The **particle model** describes how particles are arranged and how they move in different states.
The **kinetic energy** of particles increases with temperature, causing faster motion.
The **strength of forces** between particles determines whether a substance is solid, liquid, or gas.

Solids

In a **solid**, particles are **tightly packed** in fixed positions and can only **vibrate** in place.
Solids have a **definite shape** and **definite volume** because particles are held in a rigid structure.
Most solids are **crystalline** (particles in a regular pattern), but some are **amorphous** (no long-range order).
Melting a solid requires **energy** to overcome the forces holding particles together.

Liquids

In a **liquid**, particles are **close together** but can **slide past** one another.
Liquids have a **definite volume** but **no definite shape**—they take the shape of their container.
Particles in a liquid have **more kinetic energy** than in a solid, allowing them to move more freely.
Water is an exception: its solid (ice) is **less dense** than its liquid form.

Gases

In a **gas**, particles are **far apart** and move **rapidly and randomly** in all directions.
Gases have **no definite shape or volume**—they expand to fill any container.
The **kinetic energy** of gas particles is high enough to overcome most intermolecular forces.
Gases are **compressible** because there is a lot of empty space between particles.

Changes of State

**Melting**: solid → liquid (energy added, particles gain kinetic energy).
**Freezing**: liquid → solid (energy removed, particles slow down and lock into place).
**Boiling/Evaporation**: liquid → gas (energy added, particles escape from surface or throughout).
**Condensation**: gas → liquid (energy removed, particles come closer together).
**Sublimation**: solid → gas directly (e.g., dry ice).
**Deposition**: gas → solid directly (e.g., frost formation).

Temperature and Particle Motion

**Temperature** is a measure of the average **kinetic energy** of particles.
As temperature **increases**, particles move **faster** and spread apart (if possible).
As temperature **decreases**, particles move **slower** and come closer together.
At the **melting point**, particles have enough energy to break free from fixed positions.
At the **boiling point**, particles have enough energy to overcome all intermolecular forces and become gas.

Particle arrangement in solid, liquid, and gas. Solids have tightly packed vibrating particles; liquids have close but sliding particles; gases have widely spaced, fast-moving particles.

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Practice questions

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1.In which state of matter do particles have the least amount of kinetic energy?
Easy
- ASolid
- BLiquid
- CGas
- DPlasma
2.What happens to the particles of a liquid when it evaporates?
Easy
- AThey gain energy and move faster, some escape the surface
- BThey lose energy and move slower
- CThey freeze into a solid
- DThey condense into a gas
3.Which of the following is a property of a solid?
Easy
- ADefinite shape and definite volume
- BDefinite shape but no definite volume
- CNo definite shape but definite volume
- DNo definite shape and no definite volume
4.The process by which a solid changes directly into a gas is called:
Medium
- ASublimation
- BDeposition
- CMelting
- DBoiling
5.In which state of matter do particles have the greatest freedom of movement?
Medium
- AGas
- BLiquid
- CSolid
- DPlasma
6.Which statement best describes the particle arrangement in a liquid?
Medium
- AParticles are close together but can slide past each other
- BParticles are in fixed positions and only vibrate
- CParticles are far apart and move randomly
- DParticles are arranged in a regular pattern
7.A student observes that a puddle of water disappears over time. Which process explains this?
Hard
- AEvaporation
- BCondensation
- CFreezing
- DMelting
8.Which of the following is an example of a substance that undergoes sublimation at room temperature?
Hard
- ADry ice (solid carbon dioxide)
- BIce (solid water)
- CIron
- DSalt

Revision notes

## States of Matter and Particle Motion ### The Particle Model - All matter is made of tiny particles (atoms, molecules, ions). - Particles are in constant motion. The amount of motion depends on temperature. - Temperature is a measure of the average kinetic energy of particles. Higher temperature → faster particle motion. ### The Three Common States | State | Particle Arrangement | Particle Motion | Shape & Volume | |-------|---------------------|-----------------|----------------| | **Solid** | Tightly packed in fixed positions | Vibrate in place | Definite shape and volume | | **Liquid** | Close together but not fixed | Slide past each other | Definite volume, takes shape of container | | **Gas** | Far apart, little attraction | Move freely and quickly | No definite shape or volume; fills container | ### Changes of State - **Melting**: solid → liquid (at melting point) - **Freezing**: liquid → solid (at freezing point) - **Boiling**: liquid → gas (at boiling point) - **Condensation**: gas → liquid - **Sublimation**: solid → gas directly (e.g., dry ice) - **Deposition**: gas → solid directly (e.g., frost) ### Key Ideas - Adding heat increases particle motion, which can overcome forces holding particles together, causing a change of state. - Removing heat decreases particle motion, allowing forces to pull particles into a more ordered state. - During a change of state, temperature remains constant until the change is complete (energy is used to break or form bonds). ### Plasma (bonus) - A fourth state of matter where particles are charged (ions and electrons). Found in stars, lightning, neon signs. ### Important Terms - **Kinetic energy**: energy of motion. Particles in a gas have more kinetic energy than in a solid. - **Intermolecular forces**: attractions between particles that hold them together. - **Vapor**: a gas that can be liquefied by compression (below its critical temperature).

Solid: State of matter with tightly packed particles that vibrate in fixed positions, giving a definite shape and volume.
Liquid: State of matter with particles close together but able to slide past each other; has a definite volume but takes the shape of its container.
Gas: State of matter with particles far apart and moving freely; has no definite shape or volume and fills any container.
Plasma: State of matter similar to gas but containing charged particles (ions and free electrons); responds to electric and magnetic fields.
Melting: Change of state from solid to liquid when heated to the melting point.
Freezing: Change of state from liquid to solid when cooled to the freezing point.
Boiling: Change of state from liquid to gas at the boiling point, occurring throughout the liquid.
Condensation: Change of state from gas to liquid when cooled.
Sublimation: Change of state from solid directly to gas without passing through liquid (e.g., dry ice).
Deposition: Change of state from gas directly to solid without passing through liquid (e.g., frost formation).
Kinetic energy: Energy of motion; particles in a substance have kinetic energy that increases with temperature.
Intermolecular forces: Attractive forces between particles that hold them together; stronger in solids, weaker in gases.
Vapor: A gas that can be liquefied by compression alone without cooling (exists below its critical temperature).

Flashcards

What are the four classical states of matter?

Solid, liquid, gas, and plasma.

How are particles arranged in a solid?

Particles are tightly packed and held in fixed positions, only able to vibrate.

What properties does a solid have?

A solid has a definite shape and a definite volume.

How do particles behave in a liquid?

Particles are close together but can move past one another.

What are the properties of a liquid?

A liquid has a definite volume but takes the shape of its container.

How are particles arranged in a gas?

Particles are far apart and move freely.

What are the properties of a gas?

A gas has no definite shape or volume; it expands to fill its container.

What is plasma?

Plasma is a state of matter similar to gas but containing charged particles (ions and free electrons) that respond to electric and magnetic fields.

What happens to particle motion when temperature increases?

Particles gain kinetic energy and move faster.

What happens to particle spacing when temperature increases?

Particles move farther apart, causing the substance to expand.

What is melting?

Melting is the change from solid to liquid when heated above the melting point.

What is freezing?

Freezing is the change from liquid to solid when cooled below the freezing point.

What is boiling?

Boiling is the change from liquid to gas at the boiling point, where bubbles form throughout the liquid.

What is condensation?

Condensation is the change from gas to liquid when cooled.

What is sublimation?

Sublimation is the direct change from solid to gas without passing through the liquid state.

What is deposition?

Deposition is the direct change from gas to solid without passing through the liquid state.

What is a crystalline solid?

A crystalline solid has particles arranged in a regularly ordered, repeating pattern (crystal structure).

What is an amorphous solid?

An amorphous solid lacks long-range order in its particle arrangement (e.g., glass).

What is a vapor?

A vapor is a gas below its critical temperature that can be liquefied by compression alone.

What is a supercritical fluid?

A supercritical fluid is a substance above its critical temperature and pressure, where liquid and gas phases are indistinguishable.

How does pressure affect the boiling point?

Increasing pressure raises the boiling point; decreasing pressure lowers it.

What is the triple point of a substance?

The triple point is the temperature and pressure at which solid, liquid, and gas phases coexist in equilibrium.

What is the critical temperature of a substance?

The critical temperature is the highest temperature at which a liquid can exist; above it, the substance is a gas regardless of pressure.

Why does water expand when it freezes?

Water is unusual; its solid form (ice) is less dense than liquid water because the crystal structure has more space between molecules.

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