Chemistry 1011

1. Chemistry 1011 TOPIC Physical Properties of Matter TEXT REFERENCE Masterton and Hurley Chapter 9 Chemistry 1011 Slot 5

2. 9.2 Network Covalent, Ionic, and Metallic Solids YOU ARE EXPECTED TO BE ABLE TO: • Classify non-molecular solids as either network covalent solids, ionic solids, or metallic solids. • Relate the physical properties of non-molecular solids to the forces holding them together. Chemistry 1011 Slot 5

3. Network Covalent, Ionic, and Metallic Solids • Almost all substances that are gases or liquids 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 solids Chemistry 1011 Slot 5

4. Other Materials • There are also other materials with complex structures, for example • Polymers – natural and manufactured • Biological materials • Semiconductors Chemistry 1011 Slot 5

5. 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) Chemistry 1011 Slot 5

6. Some Examples - Carbon • Carbon can exist as both diamond and graphite • Both forms are network covalent solids • This site shows diagrams of both diamond and graphite structures: http://www.education.eth.net/acads/chemistry/allotropic_carbon-I.htm Chemistry 1011 Slot 5

7. Diamond • Diamond – pure carbon • Three dimensional structure based on tetrahedrally bonded carbon atoms. All single bonds • Very hard • Very high melting point • Does NOT conduct electricity • Diamond is transparent, strong, and very hard. It is a superb cutting tool. The atoms in diamond are very strongly held in position. Chemistry 1011 Slot 5

8. Diamond Structure • http://www.rensselaer.edu/dept/chem-eng/WWW/faculty/cale/classes/SMP/lecture1/sld014.htm • http://iumsc11.chem.indiana.edu/common/Minerals/diamond/diamond.htm Chemistry 1011 Slot 5

9. Carbon • Graphite – pure carbon • Two dimensional, layer structure based on carbon atoms bonded in triangular planar arrangement. Each carbon atom forms 2 single and 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 delocalized electrons from double bonds Chemistry 1011 Slot 5

10. Graphite Structure • Graphite is black, soft, and an excellent lubricant. • It is easy to separate layers of atoms in graphite, to make them slide past one another. . Chemistry 1011 Slot 5

11. 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 • Talc Chemistry 1011 Slot 5

12. Ionic Solids - Observations • All ionic compounds: • are solids at room temperature • have high melting points • have wide temperature range for liquid phase • are hard, but brittle • conduct electricity in the liquid phase and in solution Chemistry 1011 Slot 5

13. Ionic Solids • High melting and non volatile • Strong interionic attractions must be overcome in order to separate ions of opposite charge • Do not conduct in solid phase • Ions must move in order for the material to conduct electricity. Ions can only move if the substance is melted or dissolved in water • Many dissolve in water, but not in organic solvents • Water is a highly polar substance Chemistry 1011 Slot 5

14. Attractions Between Ions • The force of attraction between oppositely charged 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 = greater force of attraction, eg NaCl vs KBr http://www.scs.uiuc.edu/~chem315/solidstatestructures/naclf.htm Chemistry 1011 Slot 5

15. Metals - Observations • All metals: • are solids at room temperature (except for mercury); 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 shiny Chemistry 1011 Slot 5

16. Metal Structures • Solid metals consist of regular arrays of metal atoms forming a crystal lattice • Delocalized valence electrons form a “sea of electrons” that can move freely throughout the metal • Delocalization provides stability • The “electron sea” is also present in the liquid phase Chemistry 1011 Slot 5

17. Explaining Metal Properties • Variable melting points • Melting point depends upon the strength of the bonds. This in turn generally depends upon the number of valence electrons. However, there is no simple correlation • High liquid temperature range • Vaporizing a metal requires the valence electrons to become localized, ie the metal bonds must be broken • Ductility and malleability • Metal crystal structures are flexible, layers in the crystal lattice can slide Chemistry 1011 Slot 5

18. 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 by themselves • Shininess • Delocalized electrons absorb and emit light over a wide wavelength range Chemistry 1011 Slot 5

19. On-line materials • http://www.beyondbooks.com/psc92/3.asp Chemistry 1011 Slot 5