unit 2.1

• A liquid has a defined volume but takes the shape of its container.
• a molecule is two or more atoms held together by chemical bonds
• a molecule is two or more atoms bonded together
• Boiling points increase with increasing molecular mass, as more energy is required to overcome intermolecular forces between particles.
• The boiling point is the temperature at which a liquid changes into its gaseous state.
• Matter is a substance that has mass and occupies space
• Matter exists in three states: solid (s), liquid (l) or gas (g)
• Particle theory of matter:

  • Describes the arrangement and movement of particles in a substance
  • Used to explain the physical properties of solids, liquids, and gases
• Kinetic particle theory states that:

  • All matter is made up of tiny particles (atoms or molecules)
  • Particles are in constant and random motion
• Solid:

  • Particles are held together in fixed positions by very strong forces of attraction
  • Cannot move about freely
  • Cannot be compressed because particles are already close together
  • Particles vibrate or rotate about their fixed positions
• Liquid:

  • Particles are arranged in a disorderly/random manner with weaker forces of attraction than in solids
  • Can move about freely throughout the liquid
  • Still packed closely together
• Gas:

  • Forces of attraction between gas particles are very weak
  • Particles have a lot of kinetic energy and are not held in fixed positions
  • Particles in gas are far apart from one another, allowing for compression when pressure is applied
• Changes of State:

  • Arrangement, movement, and distance between particles change during a change of state
  • Particles themselves remain unchanged
• Melting point:

  • Temperature at which a solid becomes a liquid
• Evaporation:

  • Process by which a liquid changes to a gas below the boiling point
  • Volatile liquids evaporate quickly at room temperature
• Condensation:

  • Process by which a gas changes to a liquid
• the molar mass of a substance is equal to the sum of the masses of all the atoms that make up one mole of the substance