covalent bonding

• proton: 1, neutron: 1, electron: 0 (very small)
• Some alpha particles were deflected by the gold foil - this showed that an atom's mass and positive charge must be concentrated in one small space (the nucleus)
• Four physical processes that can be used to separate mixtures

  • filtration
  • crystallisation
  • distillation
  • fractional distillation
  • chromatography
• Compound


  Substance made of more than one type of atom chemically joined together
• Plum pudding model of the atom

  Sphere of positive charge with negative electrons embedded in it
• proton: +1, neutron: 0, electron: -1
• Niels Bohr's discovery


  Electrons orbit in fixed energy levels (shells)
• Unit conversion


  Changing the units of a measurement to a different standard unit
• 120 cm = 1.2 m
• 120 m = 12000 cm
• Unit conversion


  1. When converting to a larger unit, multiply the original value by the value in metres in standard form

  2. When converting to a smaller unit, divide the original value by the value in metres in standard form
• Particle model


  The three states of matter can be represented in the particle model
• Particle model assumptions


  • There are no forces between the particles
  • All particles in a substance are spherical
  • The spheres are solid
• The amount of energy needed to change the state of a substance


  Depends on the forces between the particles. The stronger the forces, the higher the melting or boiling point
• Covalent bonding


  Atoms can share or transfer electrons to form strong chemical bonds
• Covalent bond


  When electrons are shared between non-metal atoms
• Number of electrons shared

  Depends on how many extra electrons an atom needs to make a full outer shell
• Properties of covalent substances

  • High melting and boiling points
  • Solid at room temperature
• Properties of small molecules

  • Low melting and boiling points
  • Normally gas or liquid at room temperature
• Properties of large molecules

  • Melting and boiling points are low compared to giant covalent substances but higher than for small molecules
  • Normally solid at room temperature
• Most covalent structures do not conduct electricity because they do not have delocalised electrons or ions that are free to move to carry charge
• Graphite


  A giant covalent structure made only of carbon, with each carbon atom bonded to three others and forming hexagonal rings in layers. Each carbon atom has one spare electron which is delocalised and free to move around the structure
• Graphite


  • The layers can slide over each other because they are not covalently bonded, making graphite softer than diamond
  • The delocalised electrons are free to move through graphite, so it can carry charges and allow an electrical current to flow
• Graphene


  Consists of only a single layer of graphite
• Graphene


  • Strong covalent bonds make it a strong material that can also conduct electricity
  • Could be used in composites and high-tech electronics
• Fullerenes


  Hollow cages of carbon atoms bonded together in one molecule, can be arranged as a sphere or a tube (called a nanotube)
• Fullerenes


  • Molecules held together by weak intermolecular forces, so can slide over each other
  • Conduct electricity
• Fullerenes


  • Buckminsterfullerene (60 carbon atoms)
  • Other fullerenes with different numbers of carbon atoms arranged in rings that form hollow shapes
• Nanotubes


  • Carbon atoms arranged in cylindrical tubes
  • High tensile strength (difficult to break when pulled)
• Fullerenes can be used as lubricants and in drug delivery
• Nanotubes are useful in electronics
• Covalent bond


  A chemical bond formed by the sharing of one or more pairs of electrons between atoms
• Types of covalent substances


  • Molecular
  • Giant covalent
• Graphite


  • Giant covalent structure
  • Made only of carbon
  • Each carbon atom bonds to three others
  • Forms hexagonal rings in layers
  • Each carbon atom has one spare electron that is delocalised and free to move around the structure
• Graphite's layers can slide over each other


  Graphite is softer than diamond
• Conductivity of graphite


  The delocalised electrons are free to move through graphite, so can carry charges and allow an electrical current to flow
• Graphene


  • Consists of only a single layer of graphite
  • Strong covalent bonds make it a strong material
  • Can conduct electricity
  • Could be used in composites and high-tech electronics
• Fullerenes


  • Hollow cages of carbon atoms bonded together in one molecule
  • Can be arranged as a sphere or a tube (called a nanotube)
  • Molecules held together by weak intermolecular forces, so can slide over each other
  • Conduct electricity
• Fullerenes


  • Buckminsterfullerene (60 carbon atoms)
  • Other fullerenes with different numbers of carbon atoms arranged in rings that form hollow shapes
• Fullerenes


  • Can be used as lubricants and in drug delivery