 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




 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

 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

 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

 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 nonpolar)
 conduct electricity well because of moving sea of electrons

Melting , Boiling, and Volatility
 from highest to lowest
1.
macromolecular (giant) covalent molecules
○
 very strong intermolecular forces hold molecules together diamonds, silicon dioxide, graphite (boils at 4830 °C)
2.
metallic bonds
3.
4.
ionic bonds (cations and anions) hydrogen bonding (strong δ+ or δ-)
5.
6.
○ very strong when H is bonded with NOF ( n itrogen, o xygen, or f luorine) 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.
this flat shape allows it to stick to one another better these round shapes do
NOT allow them to stick to one another boiling point increases

Exampe: two Lewis structures for the formula
C
2
H
6
O. 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

Solubility

“like dissolves like”
 polar substances tend to dissolve in polar solvents
 non-polar substances tend to dissolve in nonpolar solvents
 dissociation of salt YouTube (:53)


+
 –

+

+
 –

+

+
 –

+
The dipoles of w a t e r attract, pushing the oil
(with no partial charge) out of the way: attractions win out over the tendency toward randomness.

+
 –

+

+
 –

+
 –

+

+

+
 –

+

+
 –

+

 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/chemistr y/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)

Type of
Bonding
Melting
Point
Boiling
Point
Volatilit y
Electrical
Conductivity
Low Low High No
Solubility in Nonpolar
Solvent
Yes
Solubilit y in
Polar
Solvent
No Nonpolar
Polar varies varies varies No No Yes
No No Yes Hydroge n bonding
Ionic
Bonding varies varies high high varies low
Metallic
Bonding high
Covalent varies high varies
Giant
Covalent
High High low varies
Low
Yes
(molten or aqueous)
Yes
No
No (except graphite)
No
No
No
No
Yes
(most)
No
No
No