Physical Properties Related to Bonding Type Topic 4.5

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

Categorize by type of bonding

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

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

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

Metallic high mp and bp low volatility 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

Categorized by physical properties

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-)

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

only normal dipole : dipole bonding can take place 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 One Lewis structure could be ethanol and one Lewis structure could be dimethyl ether. Ethanol will have a higher boiling point than dimethyl ether because ethanol exhibits hydrogen bonding and dimethyl ether exhibits dipole-dipole interactions. Hydrogen bonding is an especially strong type of dipole-dipole interaction and will thus raise the boiling point of ethanol. ethanol - higher BP dimethyl ether - lower BP

dissociation of salt YouTube (:53) 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)

12/10/99 + – + – The dipoles of water attract, pushing the oil (with no partial charge) out of the way: attractions win out over the tendency toward randomness. + –

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)

Electrical Conductivity Solubility in Non-polar Solvent Type of Bonding Melting Point Boiling Point Volatility Electrical Conductivity Solubility in Non-polar Solvent Solubility in Polar Solvent Non-polar Low High No Yes Polar varies Hydrogen bonding Ionic Bonding high low (molten or aqueous) Yes (most) Metallic Bonding Covalent Giant Covalent No (except graphite)