Bonding Structure

• Solids - Liquids - Gases

  Solids:

  • cannot be compressed
  • vibrate around a fixed point
  • fixed shape

  Liquids:

  • cannot be compressed
  • takes shape of container

  Gas:

  • can be compressed
  • particles move in all directions
• The particle model assumes that particles are solid spheres with no forces between them. However:

  • particles are not solid, since atoms are mostly empty space
  • many particles are not spherical

  Condensing and freezing

  Energy is transferred from a substance to the surroundings when a substance condenses or freezes. This is because the forces of attraction between the particles get stronger.
• • metal atoms lose electrons to form positively charged ions
  • non-metal atoms gain electrons to form negatively charged ions
• The ionic lattice


  An ionic lattice is held together by strong electrostatic forces of attraction between the oppositely charged ions

  • The forces act in all directions in the lattice
• Ionic compounds are held together by electrostatic forces between the oppositely charged ions

  • has a high boiling/melting point ——> a lot of energy is needed to overcome the strong bonds
• A substance can conduct electricity if:

  • it contains charged particles, such as ions
  • these particles are free to move from place to place

  An ionic compound can conduct electricity when:

  • it has melted to form a liquid, or
  • it has dissolved in water to form an aqueous solution


  (Ions can’t move in a solid)
• Dot & Cross and Structural formula

  Advantages + limitations of dot and cross diagram:

  • shows the pairs of outer electrons, and which atoms they have come from
  • It does not show how the atoms are arranged in space

  Advantages + limitations Of a structural formula

  • shows the bonds between atoms
  • does not show which atoms the electrons have come from
• Small Molecules


  Have:

  • strong covalent bonds
  • weak intermolecular forces that are (overcome)
  • low melting/ boiling points
• Silicon dioxide (silica)


  Found in sand:

  • has a giant covalent structure
  • strong covalent bonds
  • regular arrangement
  • high melting/boiling points —-> large amounts of energy is needed to overcome the strong covalent bonds
  • no charged particles that are free to move = can’t conduct electricity (except graphite)
• Diamond


  Has a:

  • giant covalent strucrture
  • each carbon atom is joined to four other carbon atoms
  • there are no free electrons
  • very hard
  • useful for oil rig drills
  • very high melting point
  • does not conduct electricity
• Graphite


  Has a:

  • giant covalent structure
  • each carbon forms three covalent bonds with other carbons
  • form layers of hexagonal rings
  • no covalent bonds between layers
  • one delocalised electron from each atom ( can conduct electricity) ——> they are free to move between layers
  • Useful for electrodes and lubricants
  • Weak forces ——> so layers can slide over each pther
  • makes graphite slippery
• Graphene


  Form of carbon:

  • a single layer of graphite
  • strong covalent bonds
  • has a high melting pont
  • very strong
  • conducts electricity —-> has delocalised electrons that are free to move
  • useful for electronics and composites
• Fullerenes


  Molecules of carbon with hollow shapes

  • hexagonal rings joined by covalent bonds (structure)
  • examples: buckminsterfullerene and nanotubes

  Buckminsterfullerene:

  • first to be discovered
  • made of 60 carbon atoms
  • spherical shape
  • weak intermolecular forces
  • slippery
  • low melting point

  Nanotubes:

  • rolled like a cylinder
  • high length to diameter ratios
  • high tensile strength
  • strong in tension
  • conduct electricity (delocalised electrons)
  • useful for nanotechnology and electronics
• Polymers


  have:

  • very large molescules
  • joined by covalent bonds
  • strong intermolecular forces
  • melt at high temperatures
  • solids at room temp
• Properties of metals


  they are:

  • electrical conductors (have delocalised electrons)
  • good conductors of thermal energy
  • have high melting and boiling points (metallic bonding is very strong) ——> large amounts of energy are needed to overcome the metallic bonds 
• Alloys


  Mixtures of two or more metals

  E.g. Iron + tungsten —-> steel (a hard alloy)

  Pure metal: When a force is applied, the layers may slide over each other (they are soft)

  • The greater the force needed, the harder and stronger the metal

  Alloy: atoms are in different sizes ——-> create distorted layers —-> greater force is required for the layers to slide over each other

  • alloy is hard and strong
• Nano particles


  Have a large surface area to volume ratio

  Uses:

  • electronics
  • catalysts (efficient)
  • medical treatments

  E.g. Self-cleaning window panes have nano-particulate coatings. These catalyse the breakdown of dirt in the presence of sunlight.

  risks: harmful to body (toxic substances may bind to them)