CHEMISTRY: the molecular nature of matter and change

• Chemistry is the study of matter, its properties, the changes that matter undergoes, and the energy associated with these changes
• Matter


  Anything that has both mass and volume - the "stuff" of the universe: books, planets, trees, professors, students
• Composition


  The types and amounts of simpler substances that make up a sample of matter
• Properties


  The characteristics that give each substance a unique identity
• States of Matter


  • Solid
  • Liquid
  • Gas
  • Plasma
  • Bose-Einstein condensate

  
• Solid


  • Has a fixed shape and volume. Solids may be hard or soft, rigid or flexible
• Liquid


  • Has a varying shape that conforms to the shape of the container, but a fixed volume. A liquid has an upper surface
• Gas


  • Has no fixed shape or volume and therefore does not have a surface
• Plasma


  • An electrically conducting medium in which there are roughly equal numbers of positively and negatively charged particles, produced when the atoms in a gas become ionized
• Bose-Einstein condensate (BEC)


  • A state of matter in which separate atoms or subatomic particles, cooled to near absolute zero, coalesce into a single quantum mechanical entity—that is, one that can be described by a wave function—on a near-macroscopic scale

  
• Physical Properties


  Properties a substance shows by itself without interacting with another substance (e.g. color, melting point, boiling point, density)
• Chemical Properties


  Properties a substance shows as it interacts with, or transforms into, other substances (e.g. flammability, corrosiveness)
• A physical change is a change in which the composition of a substance does not change, only the physical form changes
• A chemical change is a change in which the composition of a substance changes, resulting in the formation of one or more new substances
• Changes in physical state are reversible by changing the temperature, while chemical changes cannot simply be reversed by a change in temperature

  
• Some characteristic properties of copper

  • Color
  • Malleability
  • Ductility
  • Thermal and electrical conductivity
  • Resistance to corrosion

  
• Distinguishing between physical and chemical change

  Does the substance change composition or just change form?

  
• In a physical change, the composition of a substance does not change, only the physical form changes
• In a chemical change, the composition of a substance changes, resulting in the formation of one or more new substances
• Kinetic Theory of Matter


  Atoms are always moving, and the more energy added to the atoms, the faster and farther apart they move
• Types of Physical Changes

  • Grinding
  • Dissolving
  • Eroding
  • Ripping
  • Tearing
  • Breaking
  • Phase changes (melting, freezing, condensing, etc.)
• Examples of Physical Changes

  • Paper torn into pieces
  • Sugar dissolved into tea
  • Salt dissolved into water
  • Nails or hair cut
• Types of Phase Changes

  • Melting
  • Freezing
  • Evaporation
  • Condensation
  • Sublimation
  • Deposition

  
• Phase changes are physical changes, as the chemical composition of the substance does not change, only the physical form

  
• When molecules move faster

  They produce more friction and therefore more heat, and they spread farther apart and expand
• When molecules move slower


  They cause less friction and therefore less heat, and they move closer together and contract
• Melting


  Matter changing from a solid to a liquid, as energy is added and the particles move faster until the bonds break
• Evaporation


  Matter changing from a liquid to a gas at the surface, as energy is added to the surface and the particles at the surface move faster, breaking bonds

  
• Boiling


  Matter changing from a liquid to a gas throughout the liquid, as energy is added and the particles move faster, with some particles moving fast enough to change to gas while still in the liquid

  
• Condensation


  Matter changing from a gas to a liquid, as energy is removed and the particles move slower, allowing the attraction between them to pull them closer together

  
• Freezing


  Matter changing from a liquid to a solid, as energy is removed and the particles move even slower, allowing the attraction between them to pull them closer together

  
• Sublimation


  Matter changing directly from a solid to a gas, as heat is added rapidly and the molecules speed up and spread out

  
• Deposition


  Matter changing directly from a gas to a solid, as heat is taken away rapidly and the molecules slow down and get closer together

  
• All phase changes are physical changes, as the chemical composition of the substance does not change, only the physical form

  
• Phase changes occur when energy (heat) is added or removed from a substance
• In a chemical change, two or more substances are combined into an entirely new substance with all new properties, which cannot be changed back
• Signs of a Chemical Change

  • Fizzing or bubbling
  • Color change
  • Heat given off
  • Light given off
  • Odor
  • Heat required for reaction
  • New substance formed (precipitate, gas bubbles)

  
• Examples of Chemical Changes


  • Baking bread
  • Alka-Seltzer
  • Baking soda and vinegar
  • Rusting
  • Tarnishing
• Physical Property


  A trait of matter that can be observed or measured without changing the chemical composition of the matter
• Examples of Physical Properties

  • Color
  • Texture
  • Temperature
  • Mass
  • Volume
  • Density
  • Luster