1. Topic 4: Chemical Bonding and Structure 4.5 Metallic Bonding

2. Understandings A metallic bond is the electrostatic attraction between a lattice of positive ions and delocalized electrons

3. Understandings The strength of a metallic bond depends on the charge of the ions and the radius of metal ioin – Charge of ion Higher charge means more delocalized electrons which means stronger attraction Higher charge means stronger attraction – radius of ion Smaller radius means stronger attraction

4. Applications and Skills Explanation of electrical conductivity and malleability in metals – Malleability Ability to be pounded or hammered into sheet w/o breaking. Ions can slide past each other to rearrange shape The metallic bonds w/I lattice don’t have direction so pounding isn’t breaking bonds just moving – Electrical conductivity Mobile delocalized electrons Mobile electrons can move through structure Carry electric current (not produce….) Impurities can restrict electron movement Copper used in wiring needs high purity

5. Applications and Skills Explanation of trends in melting points of metals – Metallic bonds are strong often high mp – (some exceptions like mercury) – Mp depends on strength of attractive forces Across period – More delocalized electrons, higher ion charges, smaller radius all mean higher attraction, higher mp Down a group (alkali metals) – Ion radius increases, decreasing attractive force, decreasing mp

6. Understandings Alloys usually contain more than one metal and have enhanced properties. Explanation of the properties of alloys in terms of non-directional bonding (fact check book here) – Alloys are generally stronger the presence of other ions disrupts the flow of ions and makes it more difficult to hammer flat.

7. Common alloys Name of AlloyComponentsProperties & Uses SteelFe w/ C & other elementsHigh tensile strength but corrodes, used as structural material Stainless steelFe w/others such as Ni and CrWidely used in domestic and industrial appliances due to strength and corrosion resistance BrassCu & ZnVariety of plumbing fittings BronzeCu & Tin(Sn)Coins, medals, tools, heavy gears PewterSn, antimony(Sb) & CuDecorative objects DuraluminAl, Cu & MnAircraft, boats and machinery due to high strength and resistance to corrosion NicromeNi & CuHeating elements in toasters, electric heaters SolderPb & SnLow mp, used in joining two metals together specially in electric circuitry Sterling sliverAg & CuJewellery, art objects

8. Nature of Science Use theories to explain natural phenomena – Molten ionic compounds conduct electricity but solid ionic compounds do not – The solubility and melting points of ionic compounds can be used to explain observations.

9. International Mindedness The availability of metal resources and the means to extract them varies greatly in different countries. It is a factor in determining national wealth. As technologies develop, the demands for different metals change and careful strategies are needed to manage the suppy of these finite resources.