2.9 - Metallic Bonding & Structure

• metallic bonding


  the attraction between delocalised electrons and positive ions
• describe metallic bonding


  when metal atoms come together electrons in outer orbital share space with electrons in the outer orbital of neighbouring atoms forming a molecular orbital

  sharing occurs between all atoms touching central atom and so on

  electrons are delocalised and can more across positive lattice due to positive metal ions formed
• what holds metals together


  strong electrostatic forces of attraction between delocalised electrons and positive metal ions
• strength of metallic bond depends on

  nuclear charge: the higher it is the stronger the bond

  number of electrons donated to sea of delocalised elections: the more the stronger the bond

  atomic radii: the smaller the stronger the bond
• properties of metals


  high melting & boiling points

  high density

  good conductors of heat

  good conductors of electricity

  malleable - can be beaten into sheets

  ductile - can be pulled out into wires

  hard
• why do metals have high melting & boiling points?


  atoms are closely packed with strong electrostatic for us of attraction between positive ions and delocalised electrons so more energy needed to overcome them
• why do metals have high densities?


  atoms are packed as close as possible - close packing
• why are metals good conductors of heat?


  when a metal is heated energy is transferred to the kinetic energy store of electrons so energy is transferred by moving electrons
• why are metals good conductors of electricity?


  because of delocalised electrons

  When a potential difference is applied electrons are attracted to the positive electrode and flow through metal producing an electric current
• why are metals malleable and ductile?


  layers can slide over one another (slip) and then the structure will rearrange so electrons are still attracted to positive lattice
• how does the strength of the metallic bond affect malleability?


  the stronger the bond the less malleable the metal due to stronger electrostatic forus of attraction
• how to reduce malleability of metals


  make alloys

  atoms of different sites disrupt layers of atoms so it's harder for them to slide over one another
• why are metals hard?


  rolling layer of atoms is hindered by grain boundaries because rows of atoms don't line up properly
• metallic bonding in transition metals


  stronger bon because they can involve 3d and 4s electrons in delocalisation

  So have high melting & boiling points
• metallic bonding in molten metals


  ordered structure has broken down & metallic bonding is loosened
• best guide for strength of metals


  boiling point ass that's when bond breaks
• how do metals exist


  as giant metallic lattice structures
• 12- co-ordination


  each atom in metallic structure has 12 touching atoms: 6 atoms touching it in each layer, 3 in layer above, 3 in layer below
• 8-co-ordination


  each atom in metallic structure has 8 atoms touching it - 4 in layer above, 4 in layer below

  poached less efficiently

  notably those in group 1
• crystal grains

  regions of regularity where atoms in a piece of metal are arranged in a regular way
• grain boundaries


  where atoms are Misaligned
• dislocations


  subtle irregularities within a crystal grains
• 6 co-ordination


  Each atom in the metallic structure has 6 atoms touching it
• what determines type of co-ordination in the metallic structure?

  nuclear charge