9.2 Network Covalent, Ionic, and Metallic Solids

1 Chemistry 1011 Slot Network Covalent, Ionic, andMetallic SolidsYOU ARE EXPECTED TO BE ABLE TO: Classify non-molecular Solids as eithernetwork covalent Solids , ionic Solids , ormetallic Solids . Relate the physical properties of non-molecular Solids to the forces holding 1011 Slot 52 Network Covalent, Ionic, andMetallic Solids Almost all substances that are gases orliquids at room temperature and pressure(25oC and 1 atm) are molecular There are three distinct types of non-molecular Solids Network covalent Solids Ionic Solids Metallic solidsChemistry 1011 Slot 53 Other Materials There are also other materials with complexstructures, for example Polymers natural and manufactured Biological materials SemiconductorsChemistry 1011 Slot 54 Network Covalent Solids High melting points To melt such a solid , covalent bonds must be broken Insoluble in all common solvents For solution to occur, covalent bonds must be broken Poor electrical conductors There are no mobile electrons (EXCEPT Graphite)

2 Chemistry 1011 Slot 55 Some Examples - Carbon Carbon can exist as both diamond and graphite Both forms are Network covalent Solids This site shows diagrams of both diamond andgraphite structures: 1011 Slot 56 Diamond Diamond pure carbon Three dimensional structure based on tetrahedrallybonded carbon atoms. All single bonds Very hard Very high melting point Does NOT conduct electricity Diamond is transparent, strong, and very hard. It is asuperb cutting tool. The atoms in diamond are verystrongly held in 1011 Slot 57 Diamond Structure 1011 Slot 58 Carbon Graphite pure carbon Two dimensional, layer structure based oncarbon atoms bonded in triangular planararrangement.

3 Each carbon atom forms 2 singleand 1 double bond with its neighbours Layers held together by dispersion forces Very soft (layers slip) Very high melting point Conducts electricity as a result of delocalizedelectrons from double bondsChemistry 1011 Slot 59 Graphite Structure Graphite is black, soft, and an excellent lubricant. It is easy to separate layers of atoms in graphite, tomake them slide past one 1011 Slot 510 Other Network Covalent Solids Quartz SiO2 Three dimensional array of Si and O atoms Major component of sand Heated with CaCO3 and Na2CO3 gives glass Other silicon oxygen structures include Mica Asbestos TalcChemistry 1011 Slot 511 Ionic Solids - Observations All ionic compounds.

4 Are Solids at room temperature have high melting points have wide temperature range for liquidphase are hard, but brittle conduct electricity in the liquid phase andin solutionChemistry 1011 Slot 512 Ionic Solids High melting and non volatile Strong interionic attractions must be overcome in orderto separate ions of opposite charge Do not conduct in solid phase Ions must move in order for the material to conductelectricity. Ions can only move if the substance ismelted or dissolved in water Many dissolve in water, but not in organicsolvents Water is a highly polar substanceChemistry 1011 Slot 513 Attractions Between Ions The force of attraction between oppositelycharged ions depends on The size of the charge Greater charge = greater force of attraction,eg CaO vs NaCl The size of the ions Smaller ions get closer together = greaterforce of attraction, eg NaCl vs ~chem315/ 1011 Slot 514 Metals - Observations All metals: are Solids at room temperature (except formercury).

5 Melting points vary have a wide temperature range for liquid phase are ductile and malleable conduct electricity in the solid and liquid phase,but not in the gaseous phase have high thermal conductivity are insoluble in water or other solvents are shinyChemistry 1011 Slot 515 Metal Structures solid metals consist of regular arrays ofmetal atoms forming a crystal lattice Delocalized valence electrons form a seaof electrons that can move freelythroughout the metal Delocalization provides stability The electron sea is also present in theliquid phaseChemistry 1011 Slot 516 Explaining Metal Properties Variable melting points Melting point depends upon the strength of the in turn generally depends upon the number ofvalence electrons.

6 However, there is no simplecorrelation High liquid temperature range Vaporizing a metal requires the valence electrons tobecome localized, ie the metal bonds must be broken Ductility and malleability Metal crystal structures are flexible, layers in the crystallattice can slideChemistry 1011 Slot 517 Explaining Metal Properties Conduction of electricity Delocalized electrons are mobile. Conduction of heat Heat is carried through metals by colliding electrons Solubility Electrons cannot go into solution, nor cations bythemselves Shininess Delocalized electrons absorb and emit light over a widewavelength rangeChemistry 1011 Slot 518On-line materials