Transcript A somewhat review of bonding and characteristics

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 graphene 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
London 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
non-polar)

conduct electricity well because of
moving sea of electrons

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. London forces (weak, temporary δ+ or δ-)

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
these round
liquid state
shapes do
this flat shape
allows ittomolecules that can stick together better NOT allow
them to stick
stick to one
remain a liquid at higher temps.
to one
another
better
another
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

“like dissolves like”
› polar substances tend to dissolve in polar
solvents (ex. water dissolves ionic
compounds)
 dissociation of salt YouTube (:53)
› non-polar substances tend to dissolve in
non-polar solvents (ex. alcohol dissolves
covalent molecules)

giant network covalent molecules and
metals do not dissolve in most solvents
+
–
+
+
–
+
+
+
–
–
+
The dipoles of water
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/
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)
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 and
graphene)
No
No