1. Physical Properties Related to Bonding Type Topic 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 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

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. 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

12. 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)

14. 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. + –

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)
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)

16. 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)