4.4 Metallic bonding

Assessment Statements Describe metallic bond as the electrostatic attraction between a lattice of positive ions surrounded by delocalized valence electrons Explain the electrical conductivity and malleability of metals Students should appreciate the economic importance of these properties and the impact that the large-scale production of iron and other metals has made on the world.

Metallic bond Occurs between atoms with low electronegativities Metal atoms pack close together in 3-D, like oranges in a box. Close-packed lattice formation

Many metals have an unfilled outer orbital In an effort to be energy stable, their outer electrons become delocalised amongst all atoms No electron belongs to one atom They move around throughout the piece of metal. Metallic bonds are not ions, but nuclei with moving electrons

Physical Properties Conductivity Delocalised electrons are free to move so when a potential difference is applied they can carry the current along Mobile electrons also mean they can transfer heat well Their interaction with light makes them shiny (lustre)

Malleability The electrons are attracted the nuclei and are moving around constantly. The layers of the metal atoms can easily slide past each other without the need to break the bonds in the metal Gold is extremely malleable that 1 gram can be hammered into a sheet that is only 230 atoms thick (70 nm)

Melting points Related to the energy required to deform (MP) or break (BP) the metallic bond BP requires the cations and its electrons to break away from the others so BP are very high. The greater the amount of valence electrons, the stronger the metallic bond. Gallium can melt in your hand at 29.8 o C, but it boils at 2400 o C!

Alloys Alloying one metal with other metal(s) or non metal(s) often enhances its properties Steel is stronger than pure iron because the carbon prevents the delocalised electrons to move so readily. If too much carbon is added then the metal is brittle. They are generally less malleable and ductile Some alloys are made by melting and mixing two or more metals Bronze = copper and zinc Steel = iron and carbon (usually)

Economic importance Iron is found by certain percentages in minerals, such as iron oxides like of magnetite (Fe 3 O 4 ), hematite (Fe 2 O 3 ), and many others. Hematite- up to 66% pure could be put in a blast furnace directly for the production of iron metal 98% of iron production is destined for making steel

Who needs it? China, then Japan, then Korea are the world’s largest consumer's of iron Where does it come from? Iron rich minerals are commonly found everywhere in the world, however China, Brazil and Australia are the highest producers of iron ore mining The main constraint is the position of the iron ore relative to market, the cost of rail infrastructure to get it to market and the energy cost required to do so.

Exercise: Use the commonly accepted model of metal bonding to explain why: The boiling points of metals in the 3 rd period increase from sodium to magnesium to aluminum. Most metals are malleable All metals conduct electricity conduct electricity in the solid state.