Transcript Week 5

Solutions
&
The Ocean
Professor Bob
Kaplan University
Department of Science
 Most of the things you see and feel every
day are chemical compounds.
 Compounds consist of a combination of
atoms of two or more elements.
 Although there are 115 elements known
today, there are millions of compounds due
to the many ways atoms combine, with
thousands more discovered each year.
Electrons are shared equally by the atoms.
Most hydrogen compounds such as water H2O are
covalently bonded. 70% of earth’s surface is covered
by water. The human body is about 60-65% water.
Organic (C, H, O) compounds include:
Carbohydrates, Fats, Proteins, DNA
 Covalent bonding
 Chemical bond: A force that holds groups of
atoms together & makes them function as a
unit. Bond energy is the energy required to
break the bond.
 Ionic bonds:
Strong forces of attraction
between positively charged cations and
negatively charged anions which hold the ions
together in a crystalline lattice
Formed when an atom that readily loses electrons
reacts with an atom that has a high electron affinity.
Metal reacts w/ Non-metal
Electrons are transferred
from one atom to another to form
positive cations and negative anions.
Cl will gain one electron to be like Ar
Cl combines with Group I element ( Na )
Cl atom  Cl- anion
Na loses one electron to be like Ne
Na combines with Group VII element ( Cl )
Na atom  Na+ cation

Bond polarity is a simple result of the fact that:
Electrons are not shared equally.
In a polar covalent bond, the atom with the
stronger affinity for electrons may be shown with a
partial negative charge.

The atom with the lower affinity for electrons is
farther from the electron pair and is shown with a
partial positive charge.


Illustration of the hydrogen fluoride (HF) molecule.

The dipole is symbolized by a cross (+ end ) .

Note the arrowhead pointing in the
direction of the negative end.

Note the larger size of the molecule on the
negative end, as the unequally shared electrons
are spending more time there.

Polar molecules of any substance have attractions
between the positive end of one molecule and the
negative end of another molecule.

When the polar molecule has hydrogen at one end
and fluorine, oxygen or nitrogen at the other end,
the attractions are strong enough to qualify as
type of chemical bonding called:
Hydrogen bonding

A hydrogen bond is an attraction between the
oxygen atom of one water molecule
and a hydrogen atom in another.

Hydrogen bonds are much weaker than
covalent or ionic bonds.

Hydrogen bonding plays an important role
in the properties of water and
biochemical compounds such as
amino acids, proteins & DNA.

A solution is a homogeneous mixture in which one
substance called the solute is dispersed uniformly
in another substance called the solvent.

Water acts as the solvent (major component)
for the solute (minor component) or the substance
that is dissolved or dispersed in the solvent in
aqueous solutions.
The air we breathe is a solution of oxygen and
nitrogen gases.
 When we make solutions of coffee or tea,
we use hot water to dissolve substances from
coffee beans or tea leaves.
 In a hospital, the antiseptic tincture of iodine is a
solution of iodine dissolved in alcohol.
 The ocean is an aqueous solution of many salts
such as NaCl dissolved in water.

Dilute solutions contain very little solute.
Concentrated solutions contain a
larger quantity of solute.
Body fluids contain solute ions such as
K+ , Na+ , Cl- , H+ , HC03Solvent: Blood plasma
Significant changes in their concentrations
can be a sign of illness or injury.

Solutions, solutes and solvents may be
combinations of solids, liquids or gases.

The solution that forms has the
same physical state as the solvent.

Carbonated beverages are formed
by dissolving CO2 gas in water.

Stainless steel is a solid solution of carbon atoms
in a crystalline matrix of iron atoms.
Solutions dissolve a limited amount of solute.
 A solution that has not reached the limit of
solute that will dissolve in it is said to be
unsaturated.
 When a solution contains as much solid as
will dissolve at that temperature, it said to be
saturated.

NaCl will form a solution with water because the
Na+ and Cl- ions in the salt are attracted to the
positive and negative parts of water molecules.

In the hydration of NaCl :
Cl- ions are attracted to partially ( + ) H atoms,
Na+ ions are attracted to partially ( - ) O atoms.

This pulls charged ions from the crystalline solid,
as they become surrounded by water molecules.

When ionic compounds dissolve, the resulting
solution contains separated ions.

The conduction of electricity provides evidence
for these ions in solution.

Charged ions in solution act as mobile
charge carriers (like electrons in metals).

Sodium chloride and water together form a strong
electrolyte aqueous solution.

Solutes that dissolve in water as covalent
molecules do not conduct electricity .

Table sugar dissolves as a polar molecule, but
does not dissociate into charged ions.

Why is ethanol so soluble in water?

The ethanol molecule contains a polar O-H group,
which makes it compatible with water.

Covalently bonded substances such as elemental
gases, long chain hydrocarbon fuels, oil or grease
do not dissolve in water or other polar solvents.

Non-polar solutes require non-polar solvents.
‘Like dissolves Like’

In a covalently bonded compound such as
petroleum oil, the bonding electrons are
shared equally.

Covalent bonds are essentially non-polar.

The resulting molecule with its non-polar bonds
cannot form attractions to polar water molecules.

This prevents it from being soluble in water.
If you have come here directly from the SC155
Seminar session, please return to the KU course
platform now to continue with the live session of
discussion, questions and answers 
See you all there !
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