Bonding and structures

• Ionic bond 


  the strong electrostatic force of attraction between oppositely charged ions
• giant ionic compounds 


  giant ionic lattice

  regular lattice of positive and negative ions
• property of giant ionic lattice

  hard

  consist of regular pattern of oppositely charged ions with strong electrostatic forces of attraction between them
• property of giant ionic lattice

  brittle

  small distortion aligns ions with same charge

  so they repel each other

  giant lattice splits apart
• property of giant ionic lattice

  high melting point

  lots of energy is required to break the strong forces of attraction between the ions
• property of giant ionic lattice

  most will dissolve in water (soluble)

  water molecules able to provide enough energy to break down the ionic bonds between the oppositely charged ions
• property of giant ionic lattice

  electrical conductivity:

  charged particles able to move

  in a solid: do not conduct electricity

  ions cannot move due to strong electrostatic forces of attraction

  in a liquid: does conduct electricity

  ions are free to move and conduct the electrical charge
• movement of ions in giant ionic lattice (solid ionic compound crystal)

  vibrate in a fixed position

  prevented from moving by strong electrostatic forces of attraction
• factors affecting strength of ionic bond (& m/bp)

  higher charge on ion

  stronger bond

  higher melting point
• covalent bond 


  atoms held together by strong electrostatic forces of attraction between the positively charged nuclei and the negatively charged shared pair of electrons
• simple covalent molecules 


  contain a fixed number of atoms

  strong covalent bonds WITHIN molecules

  weak intermolecular forces BETWEEEN molecules
• electrons in covalent molecule

  localised

  cannot move
• property of simple covalent molecules 


  low melting/ boiling points

  not much energy is required to break the weak intermolecular forces
• property of simple covalent molecules 


  do not conduct electricity

  no overall charge

  electrons localised
• relationship between Mr and melting point

  higher Mr —> stronger intermolecular forces of attraction

  stronger intermolecular forces —> more energy needed—> higher melting/boiling point
• giant covalent structures 


  millions of atoms

  not molecules as they have no fixed number
• allotrope 


  a different form of the same element in the same state

  e.g. allotropes of carbon = diamond, graphite, fullerene, graphite
• diamond uses

  jewellery

  record player needles

  drills
• diamond structure 


  each carbon bonds to four other carbon atoms

  tetrahedral arrangement

  held in place by strong covalent bonds
• diamond property

  high melting point

  strong carbon-carbon covalent bonds require lots of energy to break them.

  no intermolecular forces
• diamond property 


  doesn’t conduct electricity

  electrons are localised
• diamond property

  insoluble

  too much energy is required to break the very strong carbon-carbon covalent bonds
• diamond property 


  hard

  lots of energy is required to break the very strong covalent-covalent bonds
• diamond property

  good conductor of heat

  heating causes atoms to vibrate more

  vibrates are transmitted throughout the structure effectively by the strong covalent bonds
• graphite uses

  batteries

  pencils

  machinery lubricant
• graphite structure

  layered structure

  carbon bonds to 3 other carbons

  hexagonal arrangement

  atoms held in place by string covalent bonds

  layers of hexagons held together by weak intermolecular forces
• graphite property

  less dense than diamond

  gaps between layers are twice as big as gaps between atoms within layers
• graphite property

  soft and slippery

  layers held together by weak intermolecular forces which require less energy to break them

  layers slide off each other easily
• graphite property

  high melting point

  strong covalent bonds require lots of energy to break them
• graphite property 


  conductor of electricity

  each carbon atoms only bonds to 3 other carbons so the 4th electron is delocalised and can move throughout the structure and conduct electricity
• graphite property

  insoluble

  too much energy is required to break the strong covalent bonds
• C60 fullerene structure

  simple molecular structure

  hexagonal + pentagonal carbon rings

  weak intermolecular forces between molecules
• C60 fullerene property 


  lower melting and boiling points

  less energy us required to break weak intermolecular forces
• C60 fullerene property 


  soft

  easier to break the weak intermolecular forces holding it together
• C60 fullerene property 


  does not conduct electricity

  delocalised electron contained within molecule so can’t conduct a current
• C60 fullerene uses 


  drug delivery systems

  lubricants

  catalysts
• metallic bonding 


  strong force of attraction between the positive ions and delocalised electrons
• metallic bonding structure 


  giant lattice structures

  tightly packed together

  outer shell electrons delocalised

  positive ions

  not molecules as don’t have fixed number of atoms
• metal property

  malleable and ductile

  layers of ions slide over each other when force is applied. forces of attractions aren’t affected so keeps the structure together
• metal property 


  conduct electricity

  delocalised electrons can move around the structure and conduct the electrical charge