1. Topic 4.5 Physical Properties of Bonds

2. Assessment Statements  4.5.1 Compare and explain the following properties of substances resulting from different types of bonding: melting and boiling points, volatility, conductivity and solubility.  Look at how impurities affect these properties  Solubilities of compounds in polar and non-polar solvents  Solubilities of alcohols in water being related to chain length

3. General physical properties Depend on the forces between the particles The stronger the bonding between the particles, the higher the M.P and BP MP tends to depend on the existence of a regular lattice structure

4. Impurities and Melting points An impurity disrupts the regular lattice that its particle adopts in the solid state, so it weakens the bonding. They always LOWER melting points Its often used to check purity of a known molecular covalent compound because its MP will be off, proving its contamination

5. How would this ideal heat curve look different if the substance was contaminated?

6. Volatility A qualitative measure of how readily a liquid or solid is vaporised upon heating or evaporation It is a measure of the tendency of molecules and atoms to escape from a liquid or a solid. Relationship between vapour pressure and temperature (B.P) Mostly dealing with liquids to gas, however can occur from solid directly to gas (dry ice). The weaker the intermolecular bonds, the more volatile

7. Conductivity Generally molecules have poor solubility in polar solvents like water, but if they do dissolve they do not for ions There are no charged particles to carry the electrical charge across the solution. Example: sugar dissolves in water C 12 H 22 O 11(s)  C 12 H 22 O 11(aq)

8. Dissolving sugar (covalent compound) It takes energy to break the bonds between the C 12 H 22 O 11 molecules in sucrose crystal structure. It also takes energy to break the hydrogen bonds in water so that one of these sucrose molecules can fit into solution. In order for sugar to dissolve, there must be a greater release of energy when the dissolution occurs than when the breaking of bonds occur.

9. Ionic compounds The energy needed to break the ionic bond must be less than the energy that is released when ions interact with water. The intermolecular ion-dipole force is stronger than the electrostatic ionic bond Breaks up the compound into its ions in solution.

10. Soluble salt in water breaks up as NaCl (s)  Na + (aq) + Cl - (aq) http://www.mhhe.com/physsci/chemistry/essentialchemis try/flash/molvie1.swf http://www.mhhe.com/physsci/chemistry/essentialchemis try/flash/molvie1.swf

13. Ionic compounds Held together by strong 3-d electrostatic forces. They are solid at room temperature and pressure If one layer moves a fraction, the ions charges are off and now repulsion occurs. This is the reason they are strong, yet brittle.

14. Molten or dissolved ionic compounds conduct electricity Insoluble in most solvents, yet H 2 O is polar and attracts both the + and – ions from salts

15. Covalent bonding properties Giant covalent Ex: diamond, silicon dioxide Very hard Very high MP (>1000 o C) Does not conduct Insoluble in all solvents Molecular covalent Ex: CO 2, alcohols, I 2 Usually soft, malleable Low MP (<200 o C) Does not conduct More soluble in non- aqueous solvents, unless they can h-bond

16. Solubility of methanol in water http://www.mhhe.com/physsci/chemistry/animations /chang_7e_esp/clm2s3_4.swf http://www.mhhe.com/physsci/chemistry/animations /chang_7e_esp/clm2s3_4.swf Alcohols generally become less soluble, the longer the carbon chain due to the decreasing tendency for hydrogen bonding to occur intermolecularly.

17. States of matter Physical state depends on intermolecular forces The weaker the attraction, the more likely it’s a gas, while stronger attractions indicate solid.

18. http://www.chemguide.co.uk/atoms/bonding/metal lic.html http://www.chemguide.co.uk/atoms/bonding/metal lic.html Metallic bonding review http://chemed.chem.purdue.edu/genchem/topicrev iew/bp/ch18/soluble.php http://chemed.chem.purdue.edu/genchem/topicrev iew/bp/ch18/soluble.php Solubility review http://wwwcsi.unian.it/educa/inglese/kevindb.html History involved with dissolving ionic compounds