Lesson C1 – The Kinetic Molecular Theory and Solids, Liquids, & Gases

Key Words Matter is anything that has mass and volume. (Examples: air, water, desk, hand) Mass is the amount of matter that an object contains. (Common Units: g, kg) Volume is the amount of space taken up by an object. (Common Units: mL, L, cm3)

The Kinetic Molecular Theory (KMT) All matter is made up of very small particles (atoms and molecules). There is empty space between the particles. The particles are always moving; they collide with each other and the walls of their container. Energy makes the particles move; the more energy they have, the faster they move and the farther apart they can get.

States of Matter & the KMT There are three familiar states (or phases) of matter: Solid: has a definite volume and shape (unless in small pieces, ex: sand) Liquid: has a definite volume but shape depends on its container Gas: volume and shape are determined by its surroundings

States of Matter & the KMT Solids The particles are packed together tightly, so even though a solid does not appear to move, the particles are constantly vibrating in place.

States of Matter & the KMT Liquids The particles are in contact with each other, but they can slip and slide past one another, changing their position. This slipping and sliding means liquids take the shape of their container.

States of Matter & the KMT Gases The particles have very large spaces between them (gases are mostly empty space). The particles can move freely in all directions, so gases spread out or diffuse in their container.

Changes of State All matter can change from one state to another by increasing or decreasing the energy of the substance. All substances have different specific temperatures at which they change state: Melting Point is the temperature at which a solid turns to a liquid. Boiling Point is the temperature at which a liquid turns to a gas.

Changes of State Changes of state due to increasing the heat energy: solid → liquid: melting ex: icicles melting liquid → gas: evaporation ex: puddles or clothes drying solid → gas: sublimation ex: dry ice (frozen carbon dioxide)

Changes of State Changes of state due to decreasing the heat energy: gas → liquid: condensation ex: water forming on the outside of a cold drink; rain liquid → solid: solidification ex: water freezing gas → solid: deposition ex: frost forming on window; snowflakes

Changes of State

Thermal Expansion & Contraction When energy is added to a material, you increase the kinetic energy of the particles. A common way to add energy is to add heat. Thermal Expansion is an increase in volume due to an increase in temperature; heating causes increased speed of particles and increased space between particles. Thermal Compression is a decrease in volume due to a decrease in temperature; cooling causes decreased speed of particles and decreased space between particles.