Physical Properties Related to Bonding Type Topic 4.5

1. Physical Properties Related to Bonding TypeTopic 4.5

2. Melting point(mp) - solid to liquid • Boiling point(bp) - liquid to gas • Volatility - how easily it is converted to gas • Conductivity (conducts electricity) • depends on whether the substance contains freely moving charged particles • Solubility - solute’s ability to dissolve in solvent

3. Categorize by type of bonding

4. Giant Covalent – carbon allotropes and silicon • atoms joined by strong covalent bonds • insoluble in all solvents (polar or non-polar) • high mp and bp • e- firmly held in place therefore no conductivity • exception is graphite and fullerenes that have moving electrons

5. Ionic bonding • held tight by strong electrostatic forces in between cations and anions • non-volatile, high mp, high bp • solid at room temp • hard and brittle because of lattice/crystalline structure • conductivity • non-mobile e- as solid = no • ions move freely when melted = yes • cations and ions separate when dissolved in water = yes • soluble in polar solvents like water

6. Covalent • strong intramolecular forces, weak intermolecular forces, usually liquids or gases at room temp or soft solid • strength of polarity and strength of van der Waals’ forces determine mp and bp • greater polarity = higher mp and bp • greater van der Waals’ = higher mp and bp • often dissolve in nonpolar solvents but not in strong polar solvents like water • do not conduct electricity

7. Metallic • high mp and bp • decreases going down the periodic table • harder for cations to attract the sea of electrons • increases going across the periodic table • atomic radii becomes smaller, easier to attract the sea of electrons • low volatility • not soluble in most solvents (polar or non-polar) • conduct electricity well because of moving sea of electrons

8. Categorized by physical properties

9. Melting , Boiling, and Volatility • from highest to lowest • macromolecular (giant) covalent molecules • very strong intermolecular forces hold molecules together • diamonds, silicon dioxide, graphite (boils at 4830°C) • metallic bonds • ionic bonds (cations and anions) • hydrogen bonding (strong δ+ or δ-) • very strong when H is bonded with NOF (nitrogen, oxygen, or fluorine) • dipole : dipole (δ+ or δ-) • van der Waals’ forces (weak, temporary δ+ or δ-)

10. For covalently bonded molecules • generally speaking • the greater the intermolecular force (IMF) between the molecules, the higher the melting point, boiling point, and volatility (evaporate) • more electrons help increase the van der Waals’ forces and keep the substance in the liquid state • molecules that can stick together better remain a liquid at higher temps. these round shapes do NOT allow them to stick to one another this flat shape allows it to stick to one another better boiling point increases

11. Exampe: two Lewis structures for the formula C2H6O. Compare the boiling points of the two molecules. hydrogen bonding can occur here which is the strongest type of dipole : dipole intermolecular force only normal dipole : dipole bonding can take place ethanol - higher BP dimethyl ether - lower BP

12. Solubility • “like dissolves like” • polar substances tend to dissolve in polar solvents • non-polar substances tend to dissolve in non-polar solvents • dissociation of salt YouTube (:53)

14. – – – – – – – – – + + + + + + + + + + + + + + + + + + The dipoles of water attract, pushing the oil (with no partial charge) out of the way: attractions win out over the tendency toward randomness.

15. Conductivity • substances must possess Freely Moving Charged Particles • this occurs in… • metals with their “sea of electrons” • YouTube (1:05) • molten ionic compounds (+ and – ions can move) • http://www.dynamicscience.com.au/tester/solutions/chemistry/bonding/bonding5.htm • ionic compounds in aqueous solution (dissolved in water) • water pulls apart + and – ions and allows them to move • graphite (delocalized electrons move between the layers)