chemistry

• Solids


  • Particles in very fixed arrangements
  • Particles vibrate around in fixed positions
  • Little kinetic energy
  • Strong forces between particles
• Liquids


  • Particles slightly more widely spaced apart
  • Particles not touching quite as much
  • Intermediate forces between particles
  • Particles vibrate more
  • Particles don't have fixed positions
• Gases


  • Particles further apart
  • Particles have large amounts of kinetic energy
  • Particles not held in fixed position
  • Weak forces between particles
• Melting


  Solid to liquid conversion
• Freezing


  Liquid to solid conversion
• Boiling/Evaporating


  Liquid to gas conversion
• Condensation


  Gas to liquid conversion
• In a closed container, condensation and evaporation will be occurring simultaneously
• Diffusion


  • Net movement of particles from an area of high concentration to an area of low concentration
  • Passive process that does not require energy
• Ammonia diffuses further and faster than hydrochloric acid due to its lower relative atomic mass
• Atom


  Smallest particle of a substance that can exist
• Element


  Contains only one type of atom and cannot be split by chemical means
• Compound


  Two or more elements chemically combined, cannot be separated back into constituent elements
• Mixture


  Contains two or more elements not chemically combined, can be separated into constituent components
• Molecule


  Two or more atoms bonded together
• Atom structure


  • Nucleus contains protons and neutrons
  • Surrounded by shells of electrons
• Proton


  Positive charge, mass of 1
• Neutron


  Neutral charge, mass of 1
• Electron


  Negative charge, mass of 1/2000
• Atomic number


  Number of protons in an atom
• Mass number


  Total number of protons and neutrons in an atom
• Group number


  Number of electrons in the outer shell
• Period number


  Number of electron shells
• Elements in the same group have similar chemical properties due to the same number of outer shell electrons
• Noble gases


  Group 0 elements that are highly unreactive due to full outer electron shells
• Isotopes


  Atoms of the same element with the same number of protons but different numbers of neutrons
• Ion


  Charged particle formed by gaining or losing electrons
• Ionic bonding


  1. Metal loses electrons to form positive ion

  2. Non-metal gains electrons to form negative ion

  3. Oppositely charged ions are attracted to form ionic bond
• Covalent bonding


  Sharing of electrons between two non-metal atoms to fill their outer shells
• Covalent bonding examples


  • Water (H2O)
  • Methane (CH4)
• Water (H2O) has a central oxygen atom with two hydrogen atoms coming to the side
• Hydrogen


  Has one electron in its outer shell
• Oxygen


  Has six electrons in its outer shell, which becomes full with eight electrons
• Methane (CH4) has a central carbon atom with four hydrogen atoms
• Carbon dioxide (CO2) has double covalent bonds
• Ethene (C2H4) has a central carbon-carbon double bond with four hydrogen atoms
• Giant ionic structures


  • Made up of a metal and a non-metal
  • Held together by strong electrostatic forces of attraction between oppositely charged ions
  • Have high melting and boiling points as a lot of energy is required to break the strong bonds
  • Don't conduct electricity when solid as the ions aren't free to move
  • Conduct electricity when molten/liquid as the ions are free to move
  • Are brittle and smash easily when hit as the layers of ions can slide and positive charges repel
• Giant covalent structures (diamond and graphite)

  • Have high melting points due to many strong covalent bonds that require a lot of energy to break
  • Graphite is used as a lubricant as the layers require little energy to slide off each other
  • Diamond doesn't conduct electricity as it has no free electrons, but graphite does conduct as it has a fourth free electron per carbon atom
• Covalent bond


  A shared pair of electrons, or the electrostatic attraction between a positive nucleus and a shared pair of electrons
• Simple molecular substances


  • Have low melting points due to weak intermolecular forces that require little energy to break
  • Have increasing boiling points with increasing relative molecular mass (Mr) as greater intermolecular forces require more energy to separate the molecules