Presentation on theme: "Ionic, Covalent and Metallic structures of solids"— Presentation transcript:
1 Ionic, Covalent and Metallic structures of solids
2 IntroductionWhere does the concept of bonding come from and how do we know what structures will be formed??The AtomValence electronsNow we know bonding refers to the forces which hold atoms togetherThere are three types of bonding Ionic, Covalent and Metallic
4 Ionic Ionic compounds are Solids at room temp Metal and Nonmetal Held together by electrostatic attraction between cations and anionsCrystaline solid … crystal lattice structure
5 Ionic Ionic lattices are extremely difficult structures to break apart. As a result, all ionic substances are solids with high melting points.Potassium iodide, magnesium chloride and calcium oxide. All of these ionic compounds have melting points over 500 °C.There is one method of breaking up the lattice - dissolve the ionic compound in water. Water has the ability to separate the ions from the lattice and allow them to move freely as a solution.
6 IonicIonic SolidsShape of Unit Cell determines breaking angle of crystal.3 unit cells: simple cubic, body centered cubic, face centered cubicHigh Lattice Energy makes them rigid, high melting and boiling points, etc.Rigid structure of charges means they do not conduct electricity when solid (but do when dissolved in water or liquid)
8 MetallicOnly MetalsHeld together by electrostatic attraction between positive nucleus and a sea of mobile valence electronsAlso called “delocallized covalent”Covalent = sharingDelocallized = not staying in one areaMobile electrons = goodconductors of electricityand heat
9 Metallic Bonding: Close Packing Strong and nondirectional Difficult to separate metal atomsHigh melting and boiling pointsSolid at room temperature (except mercury)Easy to move their relative positionMalleable and ductileCan be Amorphous Solid
10 Metallic Alloys: 2 or more metallic elements Substitutional Alloy All similar sizeStructure of Alloy similar to each pure metalEx: brass = copper and zinc, sterling = Ag & CuInterstitial AlloyVery different sized elementsHoles between larger atoms filled by smaller atomsEx: steel = iron & carbon; harder, stronger, less ductile than pure iron
11 Only nonmetal elements Covalent moleculesOnly nonmetal elementsCovalent compounds have no ions. Their atoms join up by sharing electrons with their neighbours in small groups or clusters of atoms called molecules.For example:You will find that covalent compounds have low melting points. They exist either as gases (methane), liquids (water) or as easily melted solids (paraffin wax).
12 Covalent moleculesThe covalent bonds inside the molecules are very strong. The molecules don't break apart easily. However the forces attracting neighbouring molecules to each other are very weak. It is therefore very easy to separate molecules from one another: e.g. ammoniaWhen a covalent compound melts or boils, it is the forces between the molecules which are broken. Very little energy is needed to make this happen, so covalent substances have low melting and boiling points.
13 Covalent Network Structures Only Nonmetal atomsGiant network of localized covalent bondsRigid like ionic crystal lattices (crystalline structures)Bonded by electrostatic attraction between shared, localized valence electrons and positive nucleus.Since e- are localizedPoor conductors of heatInsulators (do not conduct electricity)Rigid (will break before it changes shape)
14 Covalent network structures Diamond, graphite, the element silicon and silicon dioxide are examplesDiamond and Silica (glass)
15 Covalent network structures These covalent network structures need a large amount of energy to break all of the strong covalent bonds in them, so these substances have very high melting points.Unlike the ionic lattices, the covalent networks are insoluble in water - they are not broken apart by trying to dissolve them.
16 Covalent network structures Diamond vs GraphiteDiamond: crystallinehard, colorless, electrical insulatorBonded in 6-membered ringsGraphite: amorphous-likeslippery, black, electrical conductorBonded in sheets of trigonal planar arrangementsPi bonds between the layers account for the conductivity
17 Semiconductors Silicon network structures Metallic: temp & conductivity inversely proportionalSilicon Network Structures: temp & conductivity directly proportionalDoping increases conductivityReplace a small fraction of silicon with elements containing 1 more valence electron (n-type) or 1 less valence electron (p-type)
18 Compare PropertiesSulphur is easily ground, it is brittle, so it is a nonmetal. In fact it is a covalent moleculeTin can be flattened but not broken.Magnesium is not easily broken up
19 Summary Melting/boiling points Strength of bonds Examples Ionic High The ionic bond is strongSodium ChlorideCovalentLowThe covalent bond is strong intramolecularWeak intermolecularWaterCovalent networkCovalent bonds are strongDiamondMetallicVariesThe Strength of the metallic bond variesMagnesium