Biomolecules:
Carbohydrates
and Fats
Molecular Compounds
A molecule is defined as the smallest
indivisible portion of a pure compound
thatretains a set of unique chemical and
physical properties. Most molecular
compounds are formed in the reactions
between two or more nonmetals. A molecule
consists of two or more atoms bonded
together by covalent bonds. Most molecules
are much too small to be seen with the
naked eye, but there are exceptions.
diamond on an engagement ring, are giant
crystal lattices, repetitive molecules with
covalent bonds connecting the entire
structure.
Chapter 3.Chemical Compounds
KEY CONCEPTS
Naming
Molecular ,
Molecular
Binary
condensed and
Compounds Molecular Structural
Compounds Formulas
Naming of
Hydrocarbons StraightStraight-chain
and Alcohols chain
Alkyl groups
alkanes
Naming of Alkanes and
BranchedBranched- Their
chain alkyl
chain
Constitutional
groups
alkanes
Isomers
Naming
Ions:
Ions and Ionic
Name ionic
monatomic
Compounds
compounds
and
polyatomic
Names and Name and
Charges on
charges on formulas of
monatomic
polyatomic ionic
ions
ions
compounds
Properties of
ionic
Properties of
electrolytes and
compounds
Ionic
noncompared to
Compounds
electrolytes
molecular
compounds
Empirical
Molecular
Formula of a
and
Formula ans
hydrated ionic
Molecular
Weight
compound
Formulas
Biologically
Biologically
The Biological
important
important
Periodic Table
functional
elements
groups
Molecular Formulas, Condensed,
Structural and Empirical formulas
Types of Formulas
As a sample exercise, consider the organic
molecule given below. An organic
compound will contain carbon and hydrogen
atoms and possibly one or more atoms of
oxygen, nitrogen, sulfur, or phosphorus. To
view the molecule’s shape and the atoms in
each molecule most easily, the ball-andstick representation is used.
Molecular Formula
1
Molecular formula shows ratio of atoms
each element in the compound. E.g.
ethylamine: C2H7N.Amine had NH2
functional groups.
Todetermin
e the
molecular
formula
for a
compound
such as this
you must
first find
how many
atoms of each type are in the molecule. This
molecule contains two dark gray carbon
atoms, one dark blue nitrogen atom, and
seven light gray hydrogen atoms (a total of
five bonded to the two carbon atoms and
two bonded to the nitrogen atom). Since this
is an organic compound the next step is to
write the symbols for the elements in the
order CH followed by other element
symbols in their alphabetical order. In this
case, CHN. Finally, the number of atoms of
each kind in the molecule is denoted as a
subscript to the right of the element’s
symbol. The molecular formula for this
compound is
around the groups of atoms as a visual aid.
The condensed formula for the molecule is
CH3CH2NH2.
Structural Formula
Structural formula shows bonding of
important groups of atoms in the chemical
formula.
To picture how the atoms in the molecule
are bonded together, a structural formula
is used. This formula does not depict the
shape of the molecule. It only shows the
connectivity of atoms or bonds on 2-D
paper. It does not show correct bon distances
or angles. Single bonds are shown as single
like double and triple bonds are shown as
double and triple lines, respectively.For the
above molecule the structural formula is:
CH3CH2NH2.
C2H7N
Why isn’t the compound’s molecular
formula C2H7N1? Leaving out the subscript
"1" for nitrogen implies that there is only one
nitrogen atom in this compound.
Condensed Formula
Another way for writing out a molecule’s
formula is the condensed formula. This
method, unlike the molecular formula,
emphasizes groups of atoms in the molecule.
In the figure below, boxes have been drawn
2
3) Alloys: metal + metal
The names are written differently for ionic
and covalent compounds.
Naming
Molecular
or
Covalent
Compounds: Naming is done using prefixes
in front of the names of elements to indicate
number of atoms in the molecule.Last
element in the name is added an suffix
anide. E.g.PCl3- Phosphorus trichloride.
Prefixes
used:
Empirical Formula
Some experimental methods like elemental
analysis solve for the simplest ratio of atoms
in a molecule, the empirical formula. If
you are given the empirical formula CH2, its
molecular formula could be C2H4, C3H6, or
any multiple of CH2. While the empirical
formula gives the simplest possible ratio, the
molecular formula contains the total number
of atoms in the molecule.
A very important example of this occurs
with the empirical formula CH2O. The
molecular formula for formaldehyde is
CH2O. This is also the empirical formula for
acetic acid (molecular formula: C2H4O2). In
addition, glucose and fructose also have
CH2O as their empirical formula, but have
C6H12O6 as their molecular formulas. Since
they have the same molecular formulas, to
tell glucose and fructose apart requires
knowledge of their structural formulas.
1
mono
6
2
di
7
3
tri
8
4
tetra
9
5
penta
10
Naming of molecular compounds is similar
to ionic compound but prefixes are added in
front of the name of elements to indicate
number of atoms in the molecule.
Ionic Compound: AlCl3 -aluminum
Naming Chemical Compounds
chloride
Name of a chemical compound: A
Molecular
Compound:
SF6 -sulfur
substance is given systematic name of
hexafluoride
substance according to certain rules. Before
Naming Binary Molecular Compounds
the rules are made common names was
Binary molecular compounds are
given without following non-systematic
composed of only two elements. Examples
rule. There are names given while following
are H2O, NO, SF6 etc. .Sometimes these
systematic rules but have some features of
compounds have generic or common names
systematic naming omitted. You find that
(e.g., H2O is "water") and they also have
rules are not always followed like
systematic names (e.g., H2O,
everywhere and in chemistry strictly.
dihydrogenmonoxide). The common name
Chemical formula of a compound:Formula
must be memorized. The systematic nameis
gives types atoms and number each one in
more complicated but it has the advantage
the
that the formula of the compound can be
Chemical compound.The compound given
deduced from the name.
above can be classified as ionic and covalent
Common name
compound
Compound
Systematic
name
Types of Chemical Compounds
(if it has one)
1) Molecular or Covalent Compounds:
non -metal + non-metal
NF3
nitrogen trifluoride
2) Ionic compounds: metal+ non-metal
3
NO
nitrogen monoxide
note: for first element we
don't use mono- prefix
NO2
nitrogen dioxide
N2O
dinitrogen monoxide
N2O4
dinitrogen tetraoxide
PCl5
phosphorous pentachloride
SF6
sulfur hexafluoride
S2F10
disulfur decafluoride
H2O
dihydrogen monoxide
H2S
dihydrogen monosulfide
NH3
nitrogen trihydride
N2H4
dinitrogen tetrahydride
PH3
phosphorous trihydride
nitric oxide
higher oxidation #
laughing gas
nitrous oxide
Naming Straight-chain Alkanes: Simple
lower oxidaton # or n-alkanes
Simple alkanes contain all carbon
atoms in linear chain. Prefixes are used to
indicate how many carbon atoms there are
(the same prefixes are used for naming) in
the alkane.
Prefixes Number of
Condensed Structural
Name of
Carbon
water
Formula of Alkane CnH2n+2 Alkane
Atoms
hydrogen
sulfide
meth1
1
CH4
methane
ammonia
eth - 2
2
CH3CH3
ethane
prop- 3
hydrazine
but- 4
phosphine
3
CH3CH2CH3
propane
4
CH3CH2CH2CH3
butane
pent- 5
5
CH3(CH2)3CH3
pentane
Alkanes (also called the paraffin hex- 6
series) are hydrocarbons with single
hept- 7
covalent bonds between carbon, carbon or
hydrogen atoms. Alkanes are the simplest oct- 8
class of organic compounds. They contain non- 9
only tetravalent (making 4 covalent
dec- 10
bonds).Alkanes can form chains of carbon
and hydrogen atoms in straight chains,
branched chains, or in a ring.The number of
atoms in an alkane is given by a formula
CnH2n+2, where n is the number of carbon
atoms. alkenes and
alkynes):Methane CH
4 and Butane C4H8
methane – CH4
6
CH3(CH2)4CH3
hexane
7
CH3(CH2)5CH3
heptane
8
CH3(CH2)6CH3
octane
9
CH3(CH2)7CH3
nonane
Naming Alkanes
4
10
CH3(CH2)8CH3
decane
Simple Alkyl Groups
Alkyl group is obtained by removing
a hydrogen atom from an alkane. This
vacant bond on the carbon atom could be
bonded to any monovalent atom. Alkyl
group is used to understand the connection
relationship of a particular organic
compound to an alkane. Simple alkyl groups
or n-alkyl groups are obtained by removing
a hydrogen atom from the end of alkane
carbon atom chain. There are also called nalkyl groups. Alkane name is changed by
removing -ane and adding -yl from the end
of the name to show the removal of
hydrogen atom.
Greek prefixes
meth- 1
eth - 2
prop- 3
bellow.
Alkane
ofCommon
Alkyl Group
Name
Condensed Structural
Formula
Structure
CnH2n+1- (or R-)
CH3CH2CH3
propane
CH3CH3CH2CH3CH2CH2CH3
CH3CH2CH2-
butane
Complex AlkylGroup
Name of Alkyl Group
Common
Structure
ethyl
CH3CH2CH2CH2-
pent- 5
CH3(CH2)3CH2-
hex- 6
CH3(CH2)4CH2-
hexyl
hept- 7
CH3(CH2)5CH2- isobutane
CH3(CH2)6CH2-
heptyl
non- 9
sec-butyl
1methylpro
isobutyl
2methylpro
tert-butyl
1,1dimethyle
propyl
isobutane
IUPAC
Name
n-alkyl Group
isopropyl 1-methyle
methyl
but- 4
oct- 8
Name
butyl
pentyl
octyl
n-pentyl
nonyl
CH3CH2CH2CH
penty
2CH2(n-amyl)
decyl
isopentyl
isopentane
3-methylb
(isoamyl)
CH
3(CH2)7CH2- pentane
CH3CH
2CH2CH2CH3
CH3(CH2)8CH2-
dec- 10
BranchedChain Alkanes
Branched chain alkanes contain a
carbon atoms in linear chain and at least one
branch made up of one or more carbon
atoms. In the following balanced chain
alkane, methyl propane there is a threecarbon atom chain (propane) and one-carbon
atom
(methyl)
branch.
Complex
Alkyl
Groups
There are
alkyl
groups that
can be
produced
by
removing
a hydrogen atom from the middle carbon
atoms of the simple or n-alkanes or
removing a hydrogen atom from the carbon
atoms in a branched chain of alkanes. Some
of common complex alkyl groups are listed
isopentane
tertpentyl
1,1dimethylp
neopentane
neopentyl
2,2dimethylp
Naming branched chain alkanes:
Naming branched chain alkanes use the
IUPAC (International Union of Pure and
Applied Chemists) method. The steps of this
process are:
1. Identify the parent chain - the longest
line of carbons you can find
- the chain can be bent
- you should be able to trace over it with
your pencil without overlapping
2. Name the chain as you would name a
normal alkane
3. Looking at the remaining carbons,
name each group using the normal
5
prefixes & adding -yl
4. Number the parent chain
- number the chain so the carbons not on
the chain correspond with the lowest
possible numbers
5. Write the name of the compound by:
- writing the branch number, a dash, and
the name of the branch
[number - branch]
- if there is more than one type of that
branch, write the numbers separated by
commas
& then use the prefixes di, tri, tetra,
penta, etc. in front of the branch name
[number, number, number - tri
branch]
- if more than one type of branch is
named, put the branches in alphabetical
order,
separated by commas, based on their
names without prefixes
[number - branch, number,
number- di branch]
(2-ethyl, 4, 5- dimethyl...)
- then write the name of the parent chain
Structural Formula
IUPAC name
3-ethyl-4,5-dimethyloctane
Branched-chain alkane constitutional
isomers
Constitutional Isomers are molecules, which
have the same molecular formula but have
different connectivities (The Order They
Are Put Together). Alkanes can be very
simple examples of this.
With the structural formula C4H10 there are
two different isomers possible.
e.g.
e) If more than one different substituents are
attached to the main carbon chain, they are
arranged according to the alphabetical order
and separated by a hyphen. E.g.
As the number of Carbons in an
alkane increases, the number of structural
isomers also increases. This happens quite
dramatically, as is shown by the following
6
4-ethyl
table.
Number of carbon
Atoms
Possible
Isomers
1-3
1
4
2
5
3
6
5
7
9
8
18
9
35
10
75
15
4,347
20
366,319
Type II ionic compound:For metals that
can have more than one charge (type II) the
name of the metal is succeeded by the
charge or valency in capital Roman
numerals in bracketsORby using the suffix ous for the lowest charge and -ic for the
highest charge and sometimes with the
Latinised name for the metal.Compound
formed by transition metals and three main
group elements,Sn,Pb and Hg.The ionic
(cationic) charge is written as a roman
numeral after metal name to give one of the
possible charges they normally show.
Charges on monatomic ions of metals and
nonmetals
Symbols and Names of monoatomic ions:
Type I ions: Fixed Charge
Symbol
Name
H+
hydrogen ion
+
Li
lithium ion
Na+
sodium ion
+
K
potassium ion
Rb+
rubidium ion
Cs+
cesium ion
2+
Be
beryllium ion
Mg2+
magnesium ion
2+
Sr
strontium ion
Ba2+
barium ion
2+
Ra
radium ion
Zn2+
zinc ion
Note that the letters in an ion's name before
the -ide ending is the stem. For example, the
stem for bromide is brom-. Also, just in
case, the P for phosphide is a capital P.
Naming Ionic Compounds
Ionic compounds are made up of
ions.Positively charged ions are called
cations Charge is also called valency to
show strength of the ionic bond.Negatively
charged ions are called anions. The cation is
always named first. Cations can be metals or
polyatomic ions. There are two types of
ionic compounds depending on the fixed or
variable charges on the cation.
a) Type I- ionic compound
b) Type II ionic compound
Type Iionic compound: Converting name
to formula, requires the charge on
ions.Main-group (type I) elements usually
have fixed charges depending on the group
they occupy in the periodic table. .For
metals that have only one possible charge
(type I) the name of the metal is
used.Examples are Group I metals, Group II
metals, Aluminum, Zinc, Silver
Writing the formula, number of charges on
ions is written as subscripts in the reverse
order.
Symbol
HFClBrIO2S2Ca2+
N3P3As3Al3+
Type II: CationsVariable Charge
Symbol Systematic name
(Stock system)
+
Cu
copper(I)
Cu2+
copper(II)
2+
Fe
iron(II)
7
Common
name
cuprous
cupric
ferrous
Symbol S
(
2+
Hg2
m
Hg2+
m
2+
Pb
l
Fe3+
iron(III)
ferric
2+
Sn
tin(II)
stannous
Sn4+
tin(IV)
stannic
Cr2+
chromium(II)
chromous
3+
Cr
chromium(III)
chromic
Mn2+
manganese(II)
manganous
3+
Mn
manganese(III)
manganic
Names and Formulas of Polyatomic Ions
Pb4+
lead(IV)h)
plumbic
2+ iron(II)
g)
i) potassium
Co
cobalt(II)
cobalt(III) cobaltous
3+
chromate
Cochloride
cobalt(III)
cobaltic
nitrate
Ni2+
nickel(II)
nickelous
Ni4+
nickel(IV)
nickelic
k)
+ cesium
l) carbon
Auj)
gold(I) chlorine aurous
3+
tetrafluoride
Auperchlorate
gold(III)trifluoride auric
m)
dinitrogen
pentoxide
Symbols and Charges for Polyatomic
Anions
b)
aluminum
phosphate
d)
potassium
nitrate
e) calcium f) mercury(II)
sulfate
chloride
o) sulfur
hexafluoride
Answer: formula of ionic compounds
Formula
Name
For ionic compounds, the name of the
ClO4perchlorate
positive ion (cation) is given first, followed
ClO3chlorate
by- the name of the negative ion (anion).
ClO2
chlorite
There for conversion of name to formula is
ClOhypochlorite
easy
if you know the metal and nonmetal
IO4
periodate
atomic symbol and charge. Use the periodic
IO3iodate
table
to decide the charge on both the cation
IO
hypoiodite
and anion and determine the formula of the
CO32carbonate
compound(s)
formed in each case. For
2SO4
sulfate
transition metals the common ionic charges
are given in after the metal name in
parenthesis.
Writing basic ionic compound formulas.
Examples: lithium sulfidelithium =Li+1 ;
sulfide =S-2
PO33phosphite
Write
ions on a line: Li+1 S-2
2S2O3
thiosulfate
Then remove cation and anion charges and
exchange them without charge as subscripts
on the metal and nonmetal
Li+1 S-2 becomes Li2S1
Remember we omit "1" from the
subscript formula becomes Li2S
One other thing to remember: In ionic
compounds we only give simple ratio of
metal and nonmetal or, cations and anions.
Following example will illustrate this
principle.
Examples: magnesium oxidelithium =Mg+2 ;
oxide =O-2
Write ions on a line: Mgi+2O-2
Similarly,copper (II) bromide => CuBr2
Formula
Name
NO3nitrate
NO2nitrite
2CrO4
chromate
Cr2O72dichromate
CN
cyanide
MnO4permanganate
OH
hydroxide
O22peroxide
HCO3
hydrogen carbonate
HSO4hydrogen sulfate
(bisulfate)
SO32sulfite
HSO3hydrogen sulfite
3(bisulfite) PO4
phosphate
HPO42hydrogen phosphate
H2PO4dihydrogen phosphate
C2H3O2acetate(an alternate way
to write acetate is CH3COO-)
WritingFormulas of Ionic Compounds
Give formula offollowing ionic
compounds
a) sodium
chloride
n) carbon
dioxide
c)
magnesium
fluoride
8
Then remove cation and anion charges
andexchange them without charge as
subscripts on the metal and nonmetal
Mgi+2O-2becomes Mg2O2
This is not a simple ration of atoms of metal
and nonmetals (polyatomic ions) the
subscript of the formula becomes MgO
E. g. copper (II) bromide => CuBr2
a) sodium chloride- NaCl
f)
mercury(II) chloride- HgCl2 k)
chlorine
trifluoride-ClF3
b) aluminum phosphate-AlPO4
g) iron(II)
chloride-FeCl2
l) carbon tetrafluorideCF4
c) magnesium fluoride MgF2
h)
cobalt(III) nitrate-Co(NO2)3
m)dinitrogen
pentoxide-N2O5
d) potassium nitrate-KNO3
i)
potassium chromate-K2CrO4 n)
carbon
dioxide-CO2
e) calcium sulfate-CaSO4
j) cesium
perchlorate-CsClO4 o) sulfur hexafluorideSF6
Names of Ionic Compounds
Give the name of the following
compounds:
a) KCl
f) FeCl3
b) Mg3P2
g) CuCl2
c) Ca(NO3)2
h)
Na2Cr2O7
m) HNO3
d) HgCl2
i) K3PO4
e) CaO
j) CaSO3
a) KCl-Potassium chloride
f)
FeCl3Iron(III)chloride
k)
N2O-Dinitrogen
monoxide
b) Mg3P2-magnesium phosphide
g)
CuCl2Copper(II)chloride
j)
PCl3-Phosphorus
trichloride
c) Ca(NO3)2-Calcium nitrate h) Na2Cr2O7-Sodium
dichromate
m) HNO3 -Nitric acid
d) HgCl2-Mercury(II)chloride i)
K3PO4-Potassium
phosphate
n) HClO2 -Chlorus acid
e) CaO-Calcium oxide
j)
CaSO3
Calcium sulphite
o) H3PO4 -Phosphoric
acid
Names of Acids and Bases
Binary acids: made up of only two elements hydrogen and one other element.
Naming binary acids:
Begin with the prefix hydro.
Determine the "stem" - part of the name of the element
that combines with hydrogen.
Add the suffix ic.
Examples:
HF -hydro fluor ic - hydrofluor ic acid
HCl - hydro chlor ic - hydrochloric acid
HBr - hydro brom ic - hydrobromic acid
HI -hydro iod ic - hydroiodic acid
Ternary
k) N2O acids: made up of three elements - hydrogen,
oxygen,
l) PCl3 and another element.
Naming ternary acids:
Acids made up of three elements including hydrogen
Determine
n) HClO2 the "stem" - part of the name of the third
element.
The most common acid is given the suffix ic.
Add the prefix per for the acid with one more oxygen.
o) H3PO4
The suffix ous is given to the acid with one less
oxygen.
Answer: Formula and name of compounds:
Add the prefix hypo for the acid with two less oxygen
Name the cation (the metal) first and the anion
atoms.
(nonmetal) second. Monoatomic cations take their
Examples:
name from the element name. Monoatomic anions take
HClO4 - per chlor ic - perchloric acid - one more
their names from the first part of the element name and
oxygen atom.
then add
HClO3 - chlor ic - chloric acid - the most common
"-ide" to end.
form of the acid.
HClO2 - chlor ous - chlorous acid - one less oxygen
9
atom.
Compounds may be classified as ionic or
HClO - hypo chlor ous - hypochlorous acid - two less
molecular by performing some simple
oxygen atoms.
diagnostic tests. These include state of
HNO3 -nitric acid
matter, melting point, solubility in water,
HNO2 -nitrous acid
and electrical conductivity tests.
H2SO4
State of matter: Ionic compounds are solids
-sulfuric acid
at room temperature whereas molecular
H2SO3 -sulfurous acid
substances as a group are variable in their
H3PO4
states of matter - some are solids, but many
-phosphoric acid
are liquids or gases. Since all pure ionic
H3PO3
compounds are solids at room temperature
-phosphorous acid
(25°C), you can classify any pure liquid or
H3BO3 -boric acid
gas substance at room temperature as
molecular.
Naming Bases
Most bases have a formula that ends with
Melting point: Generally, molecular
OH. Naming is similar to naming salts or
substances like sugar melt at temperatures
ionic compounds: Name the metal and then
below 300°C, whereas ionic substances tend
the OH, hydroxide. Subscripts are obtained
to have higher melting points. However,
by cation charge and charge on the
melting point data alone is usually
hydroxide ion, OH .
insufficient evidence to classify a substance
NaOHsodium hydroxide
as ionic or molecular.
Ba(OH)2barium hydroxide
Solubility of solids in water: Both ionic
KOHpotassium hydroxide
and molecular compounds may or may not
NH4OHammonium hydroxide
dissolve in water, so this evidence alone
Ca (OH)2calcium hydroxide
cannot be used to classify a solid compound
as ionic or molecular. However, combined
Properties of Ionic Compounds and
with an electrical conductivity test,
Molecular Compounds
solubility tests are an excellent way of
Properties of Compounds
A compound consists of two or more atoms
classifying solids.
or ions bonded together.There are two major
Electrical conductivity test: A simple
classes of compounds defined by chemical
conductivity tester can be made using some
bonding:Ionic compounds are formed by
wire, a battery, a light bulb, and light bulb
the attractions between oppositely charged
socket. Ionic compounds dissolve in water
ions as described above.Molecular
to form electrically conductive solutions.
compounds are formed when nonmetallic
Dissolved molecular substances do not
atoms share attractionsfor each other's
conduct electricity.
electrons.Each class of compounds has
All solutions that contain dissolved ionic
unique distinguishing properties.
compounds will conduct electrical current,
Imagine that you are cleaning up tiny white
But what if the substance you want to test is
crystals that have been spilled on your
not soluble in water? In such a case
kitchen counter. How can you tell whether
You have to melt it. If the molten (liquid)
the crystals are table salt (an ionic
substance conducts electricity, then it is
compound), sugar (a molecular compound),
ionic; if it doesn’t, then it is molecular.
or something else?
Ionic Compounds
10
e.g. HCl(aq)  H+(aq)
+ Cl-(aq)
Molecular Compounds
crystalline solids
gases,
liquids, or waxy, flaky or needle-like
solids
high melting points
low
melting points
high boiling points
low
boiling points
conduct electricity when
do not
conduct electricity
molten or dissolved in water
many are soluble in water
few are
soluble in water
few are soluble in non-polar
many
are soluble in non-polar solvents
solvents
Electrolytes in Aqueous Solution
Ionic Theory of Conductivity of Solutions
The conductivity of aqueous solutions is due
to the presence of freely moving ions
(anions and cations) dissolved in water.In
the presence of an electric field the ions in
the solution begin to move, and it is the
moving charges that form an electric
current. Water itself is a poor conductor of
electricity due to each water molecule being
electrically neutral.
Electrolyte
An electrolyte is a substance that dissolves
in water to give an electrically conducting
solution. There are two different types of
electrolytes (strong and weak electrolytes)
summarized below.
Strong-ElectrolytesWeak-electrolytes and
Nonelectrolytes
Strong electrolyte
Most ionic compounds (salts)
e.g. NaCl(aq)Na+(aq) + Cl-(aq)
The single arrow indicates that the Na+ and
Cl- ions have no tendency to recombine to
form NaCl.
Some molecular compounds such as strong
acids
The single arrow indicates that the
H+ and Cl- ions have no tendency to
recombine to form HCl.
Weak electrolytes
Weak electrolytes incompletely dissociate to
form ions in solution. These substances exist
as a mixture of molecules and ions in
solution. The double arrow indicates that the
reaction is significant in both
directions. Both forward and reverse
reactions occur constantly and
simultaneously. As a result only a small
amount of reactant ionizes to form the
products. This balance between the forward
and reverse reactions produces a state of
chemical equilibrium.
Weak acids (molecular compounds)
e.g. acetic acid
(HC2H3O2)
HC2H3O2(aq)
H+(aq) +
C2H3O2-(aq)
weak bases (molecular compounds)
e.g. ammonia (NH3)
NH3(aq)+
H2O
NH4+(aq)+
OH-(aq)
A non-electrolyte is a substance that
dissolves in water to give a non-conducting
or poorly conducting solution. Molecules of
the substance mix with water molecules and
dissolve but do not dissociate to form ions in
solution. Molecules of a non-electrolyte are
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not charged and therefore do not carry an
electric current.
Here is the name: copper(II) sulfate
pentahydrate. Notice penta meaning five and
hydrate meaning water. You would use this
name both when writing the name or
speaking it.
Molecular compounds other than strong
acids, weak acids and weak bases.
That means that when you hear
"pentahydrate," you have to know to write
the dot and then the 5 H2O.
e.g. sugar (C12H22O11)
C12H22O11(s) C12H
22O11(aq)
Problems
9. Thoroughly explain the use of the mole
concept for chemical compounds (Section
3.8).
10. Calculate the molar mass of a compound
(Section 3.8).
11. Calculate the number of moles of a
compound given the mass, and vice versa
(Section 3.8).
12. Explain the formula of a hydrated ionic
compound and calculate its molar mass
(Section 3.8).
1) Suppose you heard "trihydrate." What
would you write?
2) Suppose you heard "octahydrate." What
would you write?
3) Name this substance: MgSO4 . 9 H2O
4) Write the formula for: barium chloride
dihydrate
Answers
1) trihydrate = . 3 H2O
2) octahydrate = . 8 H2O
Naming Hydrates
3) Name this substance: MgSO4 . 9
H2O: Magnesium sulfate
nonahydrate
4) Write the formula for: barium
chloride dihydrate: BaCl2. 2 H2O
Hydrates are substances that include water
into their formula.The water is not actually
part of the chemical substance and this is
reflected in the way the formula is written.
Here is the example: CuSO4 . 5 H2O
This formula means that for every one
CuSO4 in the piece of this substance you are
holding, there are also five water molecules.
No, the substance is not wet, it appears dry.
There are some hydrates that have a wet
appearance, but most appear perfectly dry to
the eye and to the touch.
Calculate the molecular weights of the
following molecular compounds: H3PO4
and H2SO4.
Click here to do more tutorials on molecule
weights from formula at another website.
Use back button to return to this page.
Molecular weight is the sum of all atomic
weights (atomic weight multiplied by their
subscripts) in the chemical Formula.
The dot IS NOT a multiplication sign.
Remember, this is chemistry, not math.
a) H3PO4: H = 1.01 g/mol, P = 30.97 g/mol,
O = 16.00 g/mol
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Notice that 1 amu is equal to 1 g/mol
c) Fe2(CO3)3
m.w. H3PO4 = 3 x 1.01 + 1 x 30.97 + 4 x
16.00 g/mol
f.w. Fe2(CO3)3 = 2 x 55.85 + 3 x 12.01 + 9 x
16.00 = 294.73 g/mol
= 98.00 g/mol
Note: you should be able to get m.w. from
name. For example: Aluminum phosphate.
b) H2SO4: H = 1.01 g/mol, S = 32.07 g/mol,
O = 16.00 g/mol
How many moles of K2SO4 are present in
180.1g of potassium sulfate?
Notice that 1 amu is equal to 1 g/mol
f.w. K2SO4 = 174.26 g/mol
This is a problem to convert g to
moles.
Conversion factor is
174.26g K2SO4 = 1 mol
m.w. H2SO4 = 2 x 1.01 + 1 x 32.07 + 4 x
16.00 g/mol
= 98.09 g/mol
Converting Grams to Moles Using Molar
Mass and Formula Mass
180.1 g K2SO4
1 mol
174.26 g K2SO4
Calculate the formula weight of following
ionic compounds: NaCl, K2CO3, and
Fe2(CO3)3.
= 1.033 mol K2SO4
Molecular compositionand Percent
Composition
Percent Composition (Percentage
Composition)
The percent composition (percentage
composition) of a compound is a relative
measure of the mass of each different
element present in the compound.
Formula weight is the sum of all weights
(i.e. atomic weight multiplied by their
subscripts) in the chemical formula of the
ionic compound.
a) NaCl: Na = 23.00 g/mol, Cl = 35.45
g/mol
Mass percent of elements in
chemical compounds are obtained
using the equation:
Notice that 1 amu is equal to 1 g/mol
f.w. NaCl = 1 x 23.00 + 1 x 35.45 g/mol
n x Atomic weight
% mass = -----------------------------x 100
molecular weight
To calculate the percent composition
(percentage composition) of a compound
follosing step are used.
 Calculate the molecular mass
(molecular weight, formula mass,
= 58.45 g/mol
b) K2CO3: K = 39.10 g/mol; C = 12.01
g/mol; O = 16.00 g/mol
f.w. K2CO3 = 2 x 39.10 + 1 x 12.01 + 3 x
16.00 = 138.2 g/mol
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formula weight), MM, of the
compound,
 Calculate the total mass of each
element present in the formula of the
compound
 Calculate the percent compositon
(percentage composition):
% by weight (mass) of element = (total mass
of element present ÷ molecular mass) x 100
Example 1
Calculate the percent by weight of sodium
(Na) and chlorine (Cl) in sodium chloride
(NaCl)
Calculate the molecular mass (MM):MM
= 22.99 + 35.45 = 58.44
Calculate the total mass of Na present:1
Na is present in the formula, mass = 22.99
Calculate the percent by weight of Na in
NaCl:
n x Atomic
weight
% mass = ----------------------------- x 100
molecular weight
%Na = ((1 x mass Na) ÷ MM) x 100 = ((1 x
22.99) ÷ 58.44) x 100 = 39.34%
Calculate the total mass of Cl present:1 Cl
is present in the formula, mass = 35.45
Calculate the percent by weight of Cl in
NaCl:
%Cl = (mass Cl ÷ MM) x 100 = (35.45 ÷
58.44) x 100 = 60.66%
The answers above are probably correct if
%Na + %Cl = 100, that is, 39.34 + 60.66 =
100.
Calculate the percent mass of oxygen
in following compounds: H2SO4,
Al2(SO4)3, and CuSO4.
n x Atomic weight
% mass = -----------------------------x 100
molecular weight
a) H2SO4: m.w. = 98.08 g/mol
Atomic weight of oxygen = 16.00
g/mol
n=4
4 x 16.00
% O mass = ---------------------------x
100 = 65.25% oxygen.
98.08
b) Al2(SO4)3: f.w. = 342.14 g/mol, Atomic
weight of oxygen = 16.00 g/mol, n = 12
12 x 16.00
% O mass = ----------------------------x
100= 56.12% oxygen.
342.14
c) CuSO4: f.w. = 159.61 g/mol
Atomic weight of oxygen = 16.00
g/mol n = 4
4 x 16.00
% O mass = -------------------------x
100= 40.01% oxygen.
159.61
Note: which compound contain lowest
amount (mass) of oxygen? Ans. CuSO4
Also remember that total of % mass of
elements in a compound should add up to
100%.
Glucose has a molecular formula of
C6H12O6 (M.W. 180.16 g/mol).
a) How many grams of C, H and O are
available in 1 mole of glucose?
b) Calculate mass percents of elements C,
H and O in glucose.
a) How many grams of C, H and O are
available in 1 mole of glucose?
Similar to problem 9. Conversion
factors are:
1 mol C6H12O6 = 6 mol C = 6 x
12.01 = 72.06g C
Mass percent of elements in
chemical compounds are obtained
using the equation:
14
1 mol C6H12O6 = 12 mol H = 12 x
1.01 = 12.12g H
1 mol C6H12O6 = 6 mol O = 6 x
16.00 = 96.00g O
1 mol C6H12O6 = 72.06g C
1 mol C6H12O6 = 12.12g H
1 mol C6H12O6 = 96.00g O
b) Mass percent of element in glucose.
C6H12O6 = 180.16 g/mol
6 x 12
%C =---------- x 100 = 40.00% C
180.16
12 x 1.01
% H = ------------- x 100
= 6.73% H
180.16
6 x 16.00
%O = ------------- x 100
= 53.29% O
180.16 ---------100.02%
Converting Percent Composition Data
into an Empirical Formula
If you assume you always have 100
g of the substance, then you can also assume
that all the percentages are really just grams
of that particular element. You must The
steps in the process are outlined below.
 Convert grams (gram ratio) into
moles or (mole ratio) by dividing
each percentage by the appropriate
atomic weight from the periodic
table.
 Convert the mole ratio into a
WHOLE NUMBER MOLE
RATIO. divide by the SMALLEST
number in the batch. That will force
the smallest whole number to be a
one (1) and the others will scale
accordingly. If you are lucky, all the
numbers will be very close to a
whole number.
 You will then have a correct
(although not accepted) mole ratio
for your formula. Moleration is same
as atom ratio since mole is just a
magnification factor of atoms.
 Atom ratio gives the empirical
formula.
Given
molar
percentages
ratios
of
elements
12.011
 2.035
2.035
C 24.44%
H 3.418% 1.0079 3.3912  2.035
 2.035
Cl 72.14% 35.453 2.035
STEP
STEP 2
divide by
1
Note: That % elemental composition
can be experimentally obtained, and
you should be able to back calculate
the molecular formula. However, in
molecules like C6H12O6 (Chemical
formula) back calculation gives only
the empirical formula.
The factor to multiply empirical
formula is obtained only when the
molecular weight is known. This
calculation is found in following
problem.
What is Empirical Formula?
Simple whole number ratio of each atom
expressed in the subscript of the formula.
Molecular Formula = C6H12O6of glucose
Empirical Formula = CH2O
Emiprical formula is calculated from %
composition
divide
by
atomic
weight
15
SMALLEST
number in
the
group
whole
number
ratios
(almost)
1.00
1.67
1.00
things. These include the big six: Carbon,
Hydrogen, Nitrogen, Oxygen,
Phosphorus(CHNOPS).
Use pf Percent Compositionto Determine
Molecular Formula knowing Molar Mass
Molar mass (MM) or molecular
weight (MW) of a molecular compound
could be measured even without knowing
the molecular formula by experiments such
as ideal gas law (M.W. = d RT/P; d is
density of a gas, R ideal gas constant, T
Kelvin temperature and P pressure of the
gas), Boiling point elevation, freezing point
depression and osmotic pressure of
solutions. The Molar mass provides the way
to calculate molecular formula from
empirical formula.
Molecular weight ofan organic compound
made up of carbon, hydrogen and oxygen
is 136 g/mole. Its elemental composition is
70.6% C and 5.9% H.What is the
empirical formula and molecular formula
of the compound?
Total of C + H = 70.6 +5.9 = 76.5 %
Since this is less than 100% remainder must
be O.
O = 100 – 76.5 = 23.5%
Assume 100 g sample and calculate moles
of each element.(grams divided by atomic
weight)
C: 70.6 g/12.01 g/moles = 5.878 mole C
H: 5.9 g/1.008 g/moles = 5.853 mole H
O: 23.5 g/16 g/moles = 1.469 mole O
Divide by smallest number to get simplified
ratio.
C: 5.878/1.469 = 4.00 = 4
H: 5.853/1469 = 3.98 = 4
O: 1.469/1.469 = 1 = 1
Therefore empirical formula = C4H4O
Empirical formula weight = (4 x 12) + (4 x
1) + (1 x 16) = 68
Since molecular weight = 136, molecular
formula must be 2 x’s empirical formula or
C8H8O2.
Biologically Important Elements
This view of the periodic table highlights the
26 elements that are important to living
The rest are generally considered trace
elements. They are often very important but
needed in much smaller amounts.
Important Functional Groups in
Carbohydrates and Fats
A functional group is a specific
combination of atoms consisting of O, H, C,
N, P and S attached to a carbon skeleton of
an alkane that affect its properties and
reactivity to be treated as a class of organic
compounds.
Major Functional Groups and Classes of
Organic Compounds:
a.HydroxylR-OH; alcohols;
E.g.ethanol
b.CarbonylR-CHO; aldehydes and
ketones; E.g.propanal and acetone
c.Carboxyl R-COOH; carboxylic
acids; E.g. acetic acid (vinegar)
d.AminoR-NH3;amines; E.g.
glycine (amino acid)
e.Sulfhydryl R-SH; thiols; E.g.
mercaptoethanol
f.Phosphate R-PO4; organic
phosphates; E.g.glycerol phosphate (in fats)
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Carbohydrates are sugars and long
polymers of sugars, such as starches and
cellulose.
Monosaccharides are single sugar units and
are also called “simple sugars”.
Disaccharides consist of two sugar units
linked together.
Polysaccharides are long polymers made of
individual sugar units, usually of the
monomer glucose.
Monosaccharides generally have molecular
formulas that are some multiple of
CH2O.Glucose (C6H12O6) is the most
important simple sugar for life.Here are
some different formulas and structures used
to represent glucose
Fats
Fats are large molecules made from two
types of building blocks, glycerol (a
polyalchohol) and fatty acids (long
hydrocarbon chains of 16-18 C with a single
carboxylic acid group at one end).They are
not polymers. Figure below shows the
structure of a fat, also known as a
triacylglycerol.
Disaccharides consist of two
monosaccharides joined together by a
covalent bond, called a glycosidic linkage.
Sucrose is a disaccharide made up of
glucose and fructose as shown below.
Fats are synthesized by the condensation of
3 fatty acids joined to one glycerol
molecule.The hydroxyl group of each
glycerol is joined to the carboxylic acid end
17
of each fatty acid by an ester linkage.
Saturated fats contain many saturated fatty
acids, those that lack double bonds in their
hydrocarbon skeleton.These are usually
solids at room temperature and are prevalent
in foods such as lard, bacon grease and
butter.
Unsaturated fats contain some unsaturated
fatty acids, which are those with one or
more double bonds.These usually are liquids
at room temperature and are in abundance in
oils, such as corn oil or olive oil.
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This page was last modified on
September 3, 2002
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