States of Matter: Solid, Liquid, and Gas

• The video discusses the three states of matter: solid, liquid, and gas.
• Substances can change from one state to another.
• The explanation relies on the particle theory.
• The particle theory, sometimes called kinetic theory, models particles as small, solid, inelastic spheres.

Solids

• There are strong forces of attraction between the particles.
• Particles are held close together in a fixed position.
• They form a regular lattice structure.
• The substance maintains a definite shape and volume.
• Solids cannot flow like a liquid, holding its form.
• Particles vibrate around, jostling against one another without changing position.
• Heating a solid causes particles to gain energy and vibrate more.
• Increased vibration weakens the forces between particles.
• At the melting point, particles gain enough energy to break free of their bonds.
• This causes the solid to melt into a liquid.

Liquids

• There are weak forces of attraction between the particles.
• Particles are free to move around randomly.
• Weak forces allow particles to stick together and remain fairly compact
• Liquids have a definite volume but can change shape.
• They can flow to fit a container.
• Heating a liquid increases particle energy and speed.
• Increased speed weakens the forces holding particles together.
• At the boiling point, particles gain enough energy to break bonds altogether.
• The liquid boils or evaporates into a gas.

Gases

• The force of attraction between particles is very weak.
• Particles are essentially free to move around independently.
• Gases do not keep a definite shape or volume.
• They fill a container by spreading out as much as possible.
• Gas particles move in straight lines, not randomly swerving.
• Particles can travel in any direction being randomly deflected by solid walls and other gas particles.
• Pressure increases when a gas is heated in a fixed container.
• Cooling a gas reduces particle energy, decreasing speed.
• Reduced energy allows forces of attraction to form bonds between particles.
• This condenses the gas into a liquid.

Changes of State

• Cooling a liquid reduces particle energy, decreasing speed.
• Reduced energy allows attractions to form more bonds and Fixing particles in place
• This freezes the liquid into a solid.
• Changes in state within a closed system do not change the mass.
• The number of particles remains the same.
• Density changes with the state of matter.
• Solids have the highest density.
• Liquids have slightly lower density.
• Gases have the lowest density.