THE DIVISION OF MATTER
MATTER
PURE SUBSTANCES
COMPOUNDS
ELEMENTS
MIXTURES
MECHANICAL
MIXTURES
(heterogenous)
SOLUTIONS
(homogenous)
SOLUTION
- a homogenous mixture of a
solute and a solvent

solute: ________________

solvent: __________________

NB. when water is the solvent we refer to it as an
aqueous solution

When a solute dissolves in a solvent NO CHEMICAL
REACTION occurs. Dissolving is a physical change.
Therefore, components of a solution can be separated
using physical properties, such as boiling point.
The Nine Solution Combinations
solvent
solute
Solid
Gas
alloys, ex. brass:
copper and zinc
brine: salt in water moth balls:
(soluble vs.
naphthalene in air
insoluble)
dental amalgam:
mercury in gold or
antifreeze:
ethylene glycol in
water (miscible
Solid
Liquid
Liquid
silver
humidity: water in
air
vs. immiscible)
Gas
hydrogen in
platinum
carbonated water:
air: oxygen in
CO2 is H2O
nitrogen
Predicting Solubility
solubility
 a physical property that describes the amount of
solute that will dissolve in a given quantity of
solvent at a specific temperature

determined by forces between the solute and
the solvent (__________________________)
 in
order for a substance to dissolve, the
forces between particles in the solute must
be _____________and new ones must be
formed between the solute and the
solvent:
forces between
the particles in
the solute must
be broken
some of the
intermolecular
forces between
particles in the
solvent must be
broken
an attraction
between the
particles of the
solute and the
solvent causes
the solute to
solubilize
FORCES BETWEEN MOLECULES:
INTERMOLECULAR FORCES

intermolecular forces are forces of attraction
__________ molecules: hydrogen bonds are the
strongest, then dipole-dipole interactions and
London dispersion forces

they are based on __________________bonds:
covalent and ionic bonds
COVALENT BONDING AND
POLARITY
nonpolar covalent bonding
 the electron pair is shared ____________,
ex. H2(g)
 "tug
of war" : linear shape
polar covalent bonding
- when an electron pair is not shared equally,
there is a localized negative charge around one
atom, represented by the symbol δ-, while the
other atom is more positively charged, δ+
- a polar covalent bond has a slightly negative
end and a slightly positive end, ex. H2O, HCl (g)
- polar molecules exhibit some
ionic character!

whether a bond is polar covalent depends on the
difference between the electronegativities of the bonded
atoms
Electronegativity

the measure of an atom's ability to attract the pair of
electrons it shares with another atom within a covalent
bond

increases up and right on periodic table

metals have a lower electronegativity than nonmetals
Polar and Nonpolar Molecules
polar molecules
 molecules that have a positively charged
end and a negatively charged end
 the slight difference in charge within a
covalent molecule is called a DIPOLE
nonpolar molecules
 do not have charged ends, ex. H2
Polarity of a molecule depends on:
1. the presence of polar covalent bonds
2. the three-dimensional shape (geometry)
of the molecule
ex. ammonia, NH3(g): polar molecule
because it contains polar covalent bonds
and a pyramidal shape
ex. methane, CH4(g): nonpolar polar
covalent bonds are all arranged
symmetrically about the central carbon:
symmetrical tetrahedral shape
Intermolecular Forces

weaker than _____________________________, but
can be stronger than ionic bonds

the temperature at which a liquid boils reflects the
________________________ needed to overcome the
attractive intermolecular forces (likewise, the
temperature at which a solid melts).


intermolecular bonds are broken when a molecular compound
melts and boils
Thus, the strength of the intermolecular forces
determines the physical properties of the substance
1) van der Waals forces
 weak
forces of attraction between
molecules, such as the dipole–dipole force
and the London dispersion force
a) dipole–dipole force (DDF)
 occurs
between ____________molecules,
such as hydrogen chloride, HCl
 the
slightly positive end of one hydrogen
chloride molecule is attracted to the
slightly negative end of a neighbouring
hydrogen chloride molecule
b) London dispersion force (LDF)

an intermolecular force of attraction that forms between
atoms of neighbouring molecules as a result of a
temporary imbalance in the position of the atoms’
electrons

forms between
__________________________________________

the side of the atoms with more electrons develops a
temporary __________charge, and the side with fewer
electrons develops a temporary ____________ charge;
if same happens to neighbouring molecule they attract
each other

since electrons move quickly, the dipole lasts for only a
fraction of a second
2. Hydrogen bonding (WATER)

water is a highly polar molecule: the difference
between the electronegativities of the oxygen
and hydrogen atoms is 1.4

since oxygen has the higher _____________
the electrons spend more time around oxygen
than they do around hydrogen, therefore the
oxygen end of a water molecule has a slightly
____________ charge while the hydrogen end
of the molecule is slightly ______________
 the
arrangement of atoms and bonds
forms a ________________________
 the
dipoles created by O-H in water are
attracted to _____________charges,
creating hydrogen bonds: the strongest
of all intermolecular forces
 water
is known as the ________________
since it is able to dissolve many more
substances than any other solvent!
Water can cause some molecular substances to _________,
including ITSELF
ie. HCl (g) + H2O (l)
-------> H3O+(aq) + Cl– (aq)
(hydronium ion)
ie H2O(l) + H2O (l)
-------> H3O+(aq) + OH– (aq)

eliminating H20 from both sides we get:
H3O+ (aq) + OH- (aq)  H2O(l)
Water causes ionic substances to
__________:
ie NaCl (s)
-------> Na+ (aq) + Cl –(aq)
INTERMOLECULAR BONDS AND SOLUTIONS
The general rule of thumb is that
_____________________________________
1. NON-POLAR SUBSTANCES
 Most covalent molecules are non-polar
 Only small molecular compounds capable of
forming hydrogen bonds will be soluble in a
polar solvent.
 ____________ solutes tend to be soluble in
_____________solvents, such as benzene or
kerosene.
2. POLAR SUBSTANCES

Result from polar covalent bonds, caused by
_________sharing of electrons between atoms.

Polar substances and substances capable of
_________bonding are soluble in polar solvents.

___________________interactions and
_____________________ increase solubility.
3. IONIC COMPOUDS

________________ attractions are attractive
forces between an ion and a polar solvent.

If the ion-dipole attractions are greater than
______________, the compound will dissolve,
and ions of ionic solutes become hydrated by
water molecules
This gives rise to miscible and immiscible
mixtures:

when two liquids dissolve in each other they are
said to be ____________, ex. ethanol and water

when two liquids do not dissolve in each other
they are said to be ______________, ex. oil and
water
Two other factors to consider are:
 i) the number of charges: compounds that
have more charges (and therefore are in a
stronger ionic bond) tend to be less
soluble.
 ii) the size of the ions involved: since small
ions bind closer together than large ions,
they tend to be less soluble
HOW DO WE KNOW WHAT TYPE OF BOND WILL
FORM?

Although no actual dividing line exists, a bond difference
of 0.4 or less is considered to be pure covalent [equal
sharing of electrons]

A bond difference between 0.4 to 1.7 is considered to be
polar covalent [unequal sharing of electrons]

a bond difference of 0.4 or less is considered to be pure
covalent [equal sharing of electrons]

a bond difference of 1.7 or greater is considered to be
ionic [loss and gain of electrons]
 In
order to truly know if a substance is
ionic or covalent, experimental data is
needed to verify that the properties do
apply
Properties of Aqueous Solutions


these are solutions that involve substances in water
there are three most common types of aqueous
solutions:
i) electrolytes
 usually formed of highly soluble ionic compounds
(formula units) that dissociate in water

conduct electricity
ii) non-electrolytes
 usually formed of covalent compounds
(molecules) that do not dissociate in water
or ionic non-soluble formula units
 do
not conduct electricity
iii) acids/bases/neutral solutions
 solutions that contain different ratios of
ions in them
- aqueous solutions can be
i) unsaturated
 a solution that will dissolve more solute
ii) saturated
 a solution that will not dissolve more solute
 a solution that is saturated with respect to one
solute can dissolve other solutes
iii) supersaturated
 formed when a saturated solution is heated to
solubilize (dissolve) more solute
Other factors affecting solubility
i) molecular size
 smaller substances dissolve easier
ii) temperature
 increase in temperature gives energy for
intermolecular bonds to be broken
 For liquids and solids, the higher the
temperature the more soluble they
become:
 since
gases expand when heated, the
higher the temperature the less soluble a
gas solute becomes
iii) pressure

affects gases more than solids or liquids: the
higher the pressure on the surface of a liquid,
the more soluble a gas solute becomes
(increase the pressure, increase the solubility of gases)