States of Matter

The Kinetic Molecular Theory KMT – describes the behavior of gases in terms of particles in motion Size: Gas particles are small Spaced very far apart No significant attractive or repulsive forces between the gas particles

The Kinetic Molecular Theory Motion: Gas particles are in constant random motion Kinetic energy is transferred when particles collide with each other or the sides of their container The collisions are elastic (no energy is lost)

The Kinetic Molecular Theory Energy: Depends on the particles mass and velocity KE = ½ mv2 Temperature is a measure of the average kinetic energy of the particles in a gas 2 gases at the same temperature have the same average kinetic energy

Explaining the behavior of gases Compression and expansion: A gas will expand to fill its container Random motion of gas particles fill the empty spaces and it expands until the container stops it. Large amounts of empty space between gas particles allow it to be compressed (squeezed into a smaller space)

Explaining the behavior of gases Diffusion refers to the movement of one material through another Gas particles flow past each other easily because there are no significant forces of attraction between them. Particles diffuse from areas of high concentration to areas of low concentration

Explaining the behavior of gases Effusion – a gas escaping through a tiny opening Gases with a higher mass effuse slower than gases with less mass Example: A tire deflating from a puncture

Gas pressure 1 atm = 101.3 kPa = 760 mm Hg = 760 Torr Pressure is force per unit area. When gas particles collide with the walls of their container, they exert pressure on the walls. SI unit for pressure is the Pascal (Pa) 1 atm = 101.3 kPa = 760 mm Hg = 760 Torr Barometer = instrument that measures pressure of the atmosphere Manometer = instrument that measures pressure of a gas in a closed container

Temperature Applies to solids, liquids, and gases Increasing the temp causes an increase in the average kinetic energy of the particles At a given temp, all particles of a substance have the same average kinetic energy Kelvin (oC+273) = SI unit of temp Absolute zero = lowest temp on Kelvin scale (0K = -273oC ~ -460oF) Movement of all particles stops at this temp

Forces of Attraction The attractive forces that hold particles together in ionic and covalent bonds are called intramolecular forces. (within the molecule) Intermolecular forces hold particles of different molecules together. (between molecules) There are three types of intermolecular forces: dispersion forces, dipole–dipole forces, and hydrogen bonds.

Liquids Liquids: Fixed volume, no fixed shape Densities are much greater than that of gases Particles are packed closer together Is a fluid – has the ability to flow and change shape

Liquids Viscosity – measure of the resistance of a liquid to flow Example: water vs. molasses Viscosity is affected by the type of intermolecular forces and by the temperature As temperature increases, viscosity decreases

Liquids Surface Tension: The particles on the surface of a liquid are being pulled down by intermolecular forces (between two molecules) The stronger the attraction between particles the stronger the surface tension

Liquids Capillary action occurs when adhesive forces are greater than cohesive forces Adhesion is the force of attraction between molecules that are different, such as water molecules and the molecules of silicon dioxide in glass. Cohesion is the force of attraction between identical molecules, such as water molecules Example: water in a graduated cylinder

Solids Solids: Particles in a solid are in constant motion (vibrating) Definite shape and volume Very strong attractive forces acting between molecules More dense than most liquids Most solids are in the shape of crystals (repeating geometric patterns)

Solids The type of ions and the ratio of ions determine the structure and the shape of the crystal.

Solids The particles in an amorphous solid are not arranged in a regular, repeating pattern and do not form crystals (they can take on different shapes). Examples of amorphous solids include glass, rubber, and many plastics.