Chemistry

• Solids have particles which are in very fixed arrangements and they vibrate around in fixed positions, they have little kinetic energy and there are strong forces between them
• Liquids have particles that are slightly more widely spaced apart, they're not touching quite as much so they have intermediate forces between them and they vibrate more and they don't have fixed positions
• Gases have particles that are further apart, they have large amounts of kinetic energy, they're not held in fixed position and there are weak forces between the particles
• Melting


  When a solid turns into a liquid
• Freezing


  When a liquid turns into a solid
• Boiling/Evaporating


  When a liquid turns into a gas
• Condensation


  When a gas turns into a liquid
• Particles with the most kinetic energy will evaporate first and leave the surface of the liquid, leaving the remaining particles with lower average kinetic energy
• In a closed container, condensation and evaporation will be occurring simultaneously
• Diffusion


  The net movement of particles from an area of high concentration to an area of low concentration, down the concentration gradient, requiring no energy as it is a passive process
• Diffusion example


  • Ammonia and hydrochloric acid in a glass tube, forming ammonium chloride as a white ring closer to the hydrochloric acid end due to ammonia diffusing faster
• Atom


  The 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
• Protons and neutrons have a mass of 1, electrons have a much smaller mass of 1/2000
• Protons have a positive 1 charge, electrons have a negative 1 charge, neutrons have no charge
• Atoms are uncharged, having equal numbers of protons and electrons
• Atomic number


  The number of protons in an atom
• Mass number


  The total number of protons and neutrons in an atom
• Group number corresponds to the number of electrons in the outer shell, period number corresponds to the number of electron shells
• Elements in the same group have similar chemical properties due to having the same number of outer shell electrons
• Noble gases


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


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


  A charged particle formed by gaining or losing electrons
• Ionic bonding


  Metal atoms lose electrons to become positive ions, non-metal atoms gain electrons to become negative ions, the oppositely charged ions are attracted to form an ionic bond
• Ionic bonding examples


  • Sodium chloride, magnesium fluoride, aluminium oxide
• 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
• Chemical structures


  • Giant covalent
  • Giant ionic
  • Giant metallic
  • Simple molecular
• Ionic bond


  Electrostatic forces of attraction between oppositely charged ions
• Giant ionic structures


  • Have high melting and boiling points due to strong electrostatic forces
  • Don't conduct electricity when solid as ions aren't free to move
  • Conduct electricity when molten/liquid as ions are free to move
  • Are brittle as layers of ions with same charge repel when force is applied
• Diamond


  • Has a giant tetrahedral structure with many strong covalent bonds
  • Has a high melting point
• Graphite


  • Has a structure of carbon atoms bonded in layers
  • Has a slightly lower melting point than diamond
  • Is used as a lubricant as the layers can slide over each other
  • Conducts electricity due to free electrons