C2

• States of matter


  Solid, liquid, gas
• Melting and freezing


  Take place at the melting point
• Boiling and condensing


  Take place at the boiling point
• Energy needed to change state

  Depends on the strength of the forces between the particles
• Particle theory model


  Particles represented by small solid spheres
• Gas particles


  • Widely spaced, in constant quick motion, collisions are frequent and elastic, weak forces between particles
• Liquid particles


  • Closely spaced, in constant motion, colliding, forces between particles less than in solid
• Solid particles


  • Can only vibrate in a fixed position
• Pure elements and compounds melt and boil at specific temperatures
• Melting point and boiling point data can be used to distinguish pure substances from mixtures
• Melting point curve


  Temperature stays horizontal when solid is melting as heat is absorbed to break bonds
• Chemical equations


  States of matter shown as (s), (l) and (g), with (aq) for aqueous solutions
• Ionic bonding


  Occurs in compounds formed from metals combined with non-metals
• Electron transfer in ionic bonding

  Metal atoms lose electrons to become positively charged ions, non-metal atoms gain electrons to become negatively charged ions
• Dot and cross diagram


  Represents electron transfer in ionic bonding
• Ionic bond


  Electrostatic force of attraction between oppositely charged ions
• Common charges of ions

  • Group 1 = +1, Group 2 = +2, Group 6 = -2, Group 7 = -1
• Working out formulae for ionic compounds

  Combine ions so total positive charge equals total negative charge
• Brackets in ionic formulae

  Used when there are two or more of a compound ion
• Giant ionic structure


  Ionic compounds are a giant structure of ions held together by strong electrostatic forces of attraction
• Properties of ionic substances

  • High melting and boiling points, do not conduct electricity when solid but do when molten or dissolved
• Covalent bonding

  Occurs in non-metallic elements and compounds of non-metals, atoms share pairs of electrons
• Covalent substances


  May consist of small molecules, have relatively low melting and boiling points, do not conduct electricity
• Size of molecule


  Larger molecules have stronger intermolecular forces, higher melting and boiling points
• Polymers


  Very large molecules, atoms linked by strong covalent bonds, intermolecular forces between polymer molecules are relatively weak
• Small molecular covalent substances


  Substances that consist of small molecules, usually gases or liquids that have relatively low melting points and boiling points
• Small molecular covalent substances

  • Have only weak intermolecular forces between the molecules
  • Intermolecular forces are overcome, not the covalent bonds, when the substance melts or boils
  • Require little energy to overcome intermolecular forces
  • Do not conduct electricity because the molecules do not have an overall electric charge
• Molecular representation


  Molecules can be shown with sticks to represent covalent bonds or shown in a 3D way
• Polymers


  • Very large molecules (not giant covalent structures)
  • Atoms in polymer molecules linked by strong covalent bonds
  • Intermolecular forces between polymer molecules are relatively strong, so they are solids at room temperature
  • Intermolecular forces are broken when a polymer melts
• Polymer representation


  • C-C-H-H-H-H-n
• Giant covalent substances


  • Solids with very high melting points
  • All atoms linked by strong covalent bonds
  • Bonds must be overcome to melt or boil
• Giant covalent substances


  • Diamond
  • Graphite
  • Silicon dioxide (silica)
• Diamond


  • Each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure
  • Very hard
  • Very high melting point
  • Does not conduct electricity
• Graphite


  • Each carbon atom forms three covalent bonds with three other carbon atoms, forming layers of hexagonal rings
  • High melting point
  • Layers free to slide over each other, so graphite is soft and slippery
  • One electron from each carbon atom is delocalised, allowing graphite to conduct thermal energy and electricity
• Graphene


  A single layer of graphite, one atom thick
• Fullerenes


  • Molecules of carbon atoms with hollow shapes, based on hexagonal rings but may also contain five or seven carbon atom rings
  • First fullerene discovered was Buckminsterfullerene (C60) with a spherical shape

  
• Carbon nanotubes


  • Cylindrical fullerenes with very high length to diameter ratios
  • Useful for nanotechnology, electronics and materials
• Metallic bonding


  • Giant structures of atoms arranged in a regular pattern
  • Electrons in the outer shell of metal atoms are delocalised and free to move through the whole structure
  • Sharing of delocalised electrons gives rise to strong metallic bonds
• Metallic bonding representation


  Delocalised electrons between positive ions
• Properties of metals


  • Strong metallic bonding means high melting and boiling points
  • Good conductors of electricity due to delocalised electrons
  • Good conductors of thermal energy due to delocalised electrons