Topic 4.5 Physical Properties and Bonding Types

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 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
 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
Categorized by physical
properties
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. ionic bonds (cations and anions)
4. hydrogen bonding (strong δ+ or δ-)
○ very strong when H is bonded with NOF (nitrogen,
oxygen, or fluorine)
5. dipole : dipole (δ+ or δ-)
6. 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
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
ethanol - higher BP
only normal dipole : dipole
bonding can take place
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 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/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
Solubility
in Nonpolar
Solvent
Solubilit
y in
Polar
Solvent
Nonpolar
Low
Low
High
No
Yes
No
Polar
varies
varies
varies
No
No
Yes
Hydroge
n
bonding
varies
varies
varies
No
No
Yes
Ionic
Bonding
high
high
low
Yes
(molten or
aqueous)
No
Yes
(most)
Metallic
Bonding
high
high
low
Yes
No
No
Covalent
varies
varies
varies
No
No
No
Giant
Covalent
High
High
Low
No (except
graphite)
No
No

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