S2.3: The Metallic Model Flashcards
What is metallic bonding?
Close-packed lattice of metal cation in a ‘sea’ of delocalized electrons
Metallic bonding in non-directional
-> doesn’t matter how cations oriented
What the theory of metallic bonding?
Metals -> low number of valance electrons
-> energy required to remove is low
Electrons detached -> delocalized -> free to move thought the structure
Atoms become positively charged -> repel and keep and lattice shape
= Strong electrostatic forces between cations and sea of delocalized electrons
Properties of metals: malleability
Can be beaten into shape with a hammer (opposite of bitter)
Metal cation layers slide
Attractive forces between metal ions and electron -> all directions
-> when slide -> metallic bonds are reformed
Lattice not broken -> reshaped
Properties of metals: strength
Metallic compounds are strong and hard
Strong attractive forces between ions + sea of electron
Properties of metals: electrical conductivity
Current carried by delocalized electrons
-> move freely though metal structure (also true for graphite)
-> metal = low resistance
Potential difference: delocalized electrons repel away from the negative terminal towards the positive terminal
Number of outer electrons increase across period -> number of delocalized electrons increase
-> conductivity increase across a period
Properties of metals: thermal conductivity
Metal -> good conductor bc of behavior of cations+electrons
Metal heated ->
cations vibrate vigorously (thermal energy increases) ->
transfer kinetic energy as they collide (to both other cations and electrons) ->
KE is transferred rapidly throughout metal ->
conduct heat very well
Although there is friction as a result of movement -> no chemical change
Properties of metals: ductile
Can be drawn into a wire
Due to close packed layers being able to slide over each other without breaking bonds
Metal fatigue: metal breaks after being bent too much
Properties of metals: melting and boiling points
Most metal -> high bp and mp -> metallic bonding strong
-> strong electrostatic forces of attraction between cations and electrons -> lots of energy to overcome
+ mobile charge = + mp, bp
What factors determine the strength of metallic bonds?
Charge of the metal ion:
+ charge -> + electrons -> + difference between ion and electron -> + electrostatic attraction -> + metallic bond
Radius of metal ion:
Smaller ionic radii -> greater attraction on the sea of electrons
Greater attraction -> stronger metallic bond -> more energy to break
What trends effect the melting point of metals?
Strength of electrostatic attraction can be increased by:
Increasing number of delocalized electrons/metal atom
Increasing number of positive charges on the metal centers in the lattice
Decreasing size of metal ion
Also:
How will the metals are packed -> why mp of periods are less clear
Melting point of metals across a period
Ex: Na, Mg, Al
-> number of valance electrons increases
-> Al -> smaller ion
= Al has strongest metallic bond
= most energy needed to break bond -> highest mp
Across a period -> mp increases
Melting points of metals down a group
Down a group -> cation size increases
-> decreased attraction between electrons + ions
-> reduction in mp
Down a group -> charge density of cations decreases -> attraction between cations and electrons decreases
How are metals chosen for a particular job?
Based on their properties:
Malleability/ductility
Mp/bp
Density
Reactivity
Electrical conductivity
Strength
Toxicity
Lustre
Thermal conductivity
Strength : weight ratio
Corrosion resistance
Sonority
Ex:
- aluminium used in food cans (non toxic and resistant to corrosion and acidic food stuffs)
- copper is used in electrical wiring (good electrical conductor and malleable/ductile)
- stainless steel is used in cutlery (strong and corrosion resistant)
