structure and bonding

• ionic bonding

  • metal + non-metal bonds
  • giant structure of ions
  • held together by strong electrostatic forces that act in all direction between oppositely charged ions
  • high melting and boiling point
  • conducts electricity when molten or in a solution
• metallic bonds:

  • occurs in metallic elements and alloys
  • giant structure in which electrons are delocalized
  • regular arrangement of positive ions held together by electrostatic attractions to the delocalized electrons
• properties of metallic bonds

  • strong and hard
  • high melting and boiling point
  • delocalized electrons move freely and carry a charge
  • layers in pure metal have a regular arrangement
• copper is used to make water pipes because it doesnt react with water and is easily bent to shape
• alloys are mixtures of metals and atleast one other element these are stronger than pure metals as the layers are distorted and cant slide over each other easily
• steels are alloys of iron made by mixing small quantaties of carbon and other metals to make steel
• steel with high carbon create a hard and strong material
• steel with low carbon create soft and easily shaped material
• stainless steel is created by adding chromium and nickel to create hard materials that are resistant to corrosion
• pure copper , gold and alluminium are too soft so alloys are created

  • gold + silver
  • copper + zinc = brass
  • copper + tin = bronze
• 24 carat gold is 100% gold
• aluminium alloys -

  • low density
  • high strenght
  • for planes and cans
• bronze

  • copper + tin
  • bright colour
  • for statues
• covalent bonding can presented in

  • energy level diagrams
  • dot and cross diagrams
  • stick diagrams
• simple covalent bonds:

  • cannot conduct electricity
  • low melting and boiling point
  • weak intermolecular forces
• covalent bonds is a shared pair of electron between atoms
• graphite

  • giant covalent structure
  • high melting point
  • each carbon atom froms three covalent bonds with other carbon atoms
  • layered hexagonal structure
  • layers are held by weak intermollecular forces
  • layers can slide so graphite is soft and slippery
  • one electron is delocalized
• silicone dioxide or silica

  • similiar structure to diamond
  • each oxygen atom is joined to two silicon atoms
  • each silicon atom is joined to four oxygen atoms
• catalyst need a large surface area to improve effectiveness
• biggest to smallest particle;

  • course particle (dust) : contains many thousand atoms
  • fine particle : contains several thousand atoms
  • nonometer : 1-100nm its only a few hundred atoms
• as particle size decreases by 10 times sa:v increases 10 times
• limitations of bonding diagrams:

  • do not tell you the shape of the molecule
  • (stick diagrams)- cannot tell how many electrons are not bonded , cannot tell where electrons come from
  • (ball and stick) alot of space
  • only small part of the lattice shown
• diamond

  • giant rigid lattice
  • each carbon atom have 4 strong covalent bonds with other carbon atoms
  • very hard
  • no charged particles cannot conduct electricity
• polymers:

  • consists of very large molecules
  • plastics are synthetic polymers
  • atoms withing polymers are held by strong covalent bonds
  • intermoleculare bonds are strong between the large polymers
  • solid at room temp
• graphene

  • single layer of graphite
  • hexagonal structure just one atom thick
  • very strong
  • good thermal thermal and electrical conductor
  • nearly transparent
  • useful as electronics and composite material
• carbon nanotubes:

  • cylindrical fullerenes with high length to diameter ratios
  • very useful for nonotechnology , electronics and materials
  • fullerenes are used to deliver drugs in the body
  • lubricants
  • as catalysts
  • reinforcing material
  • tennis racket frames
• nanoparticle:

  • high surface : volume ratio
  • uses small quantity as catalyst

  uses

  • medecine
  • suncream
  • cosmetics
  • deoderant
  • electronics
  • catalyst

  a risk

  • absorbed into body cells
  • unknown potential long term effects
• fullerenes

  • hexagonal rings of carbon atoms
  • sometimes the rings contain 5-7 carbon atoms
  • molecules have a hollow shape including tubes, balls and cages
  • first fullerene dicovered was buckministerfullerene $C_{60}$
  • consists of 60 carbon atoms
  • joined in a series of hexagons and pentagons
  • most symmetrical and therefore most stable fullerene
• brass

  • copper + zinc
  • hard wearing
  • resistant to corrosion
  • for water taps
  • door fittings