Chapter 3 : Molecules, Compounds and
Chemical Equations
Hydrogen, Oxygen and Water
elements combine together to make an almost limitless
number of compounds
Outline
the properties of the compound are totally different from
the constituent elements
1) Chemical Bonds
2) Chemical Formulas and Molecular Models
3) Ionic Compounds
4) Molecular Compounds
5) Formula Mass
6) Composition of Compounds
7) Writing and Balancing Chemical Equations
Chemical Bonds
Chemical Bonds
Types of Chemical Bonds
two general types of bonding between atoms found in
compounds, ionic and covalent
„compounds
are made of atoms held together by
chemical bonds
ionic bonds result when electrons have been transferred
between atoms, resulting in oppositely charged ions
that attract each other
covalent bonds result when two atoms share some of
their electrons.
Chemical Bonds
Chemical Bonds
1
Chemical Formulas
Empirical Formulas – simplest formula for a compound;
Chemical Formula – a symbolic representation designed to
indicate (at a minimum) the elements present and the relative
number of atoms of each element.
gives the types of atoms present and their relative
numbers.
Molecular Formulas – based on an actual (existing)
molecules.
Empirical and molecular formulas give no info on how
the atoms are attached to each other.
Three kinds of chemical formulas
1)Empirical Formula
2)Molecular Formula
3)Structural Formula
Structural Formulas – shows the order in which atoms are
bonded together in a molecule and what types of bonds.
There are different types of structural formulas.
Representing Compounds
Example Ethylene Glycol (1,2 - ethanediol)
Representing Compounds
Elements and Compounds
Empirical Formula – CH3O
Molecular Formula – C2H6O2
Structural Formulas
OH
H2C
OH
CH2
Structural
model
Ball and Stick model
Space Filling
model
Condensed
structural
model
atomic elements
molecular elements
molecular compounds
ionic compounds
CH2(OH) CH2(OH)
Representing Compounds
Elements and Compounds
2
Molecular Elements
Compound
Ionic or Molecular ?
CaBr2
Fe2O3
PCl5
AlCl3
H2O
Elements and Compounds
Ionic Compounds and their Formulas
„metals
Elements and Compounds
Ionic Compounds
Example : Sodium Chloride
+ nonmetals
„no individual molecule units, instead have a 3dimensional array of cations and anions made of
formula units
• Each Na+ ion is surrounded
by six Cl- ions (and vice
versa)
• Can’t assign one Cl- ion
exclusively to one Na+ ion
• Ratio of Na+ to Cl- is 1:1
„
many contain polyatomic ions
‰
several atoms attached together in one ion
Elements and Compounds
Ionic Compounds
3
Ionic Compounds : Formulas
„
Guide to Writing Ionic Formulas
compound must have no total charge, therefore
we must balance the numbers of cations and
anions in a compound to get 0 for a net charge.
1.
2.
3.
4.
„if
Na+
S2-,
is combined with
you will need 2
ions for every S2- ion to balance the
charges, therefore the formula must be Na2S.
Na+
5.
Write the symbol for the metal cation and its charge
Write the symbol for the nonmetal anion and its charge
Charge (without sign) becomes subscript for other ion
Reduce subscripts to smallest whole number ratio
Check that the sum of the charges of the cation
cancels the sum of the anions
Ionic Compounds
Ionic Compounds
Naming Ionic Compounds
Old Exam Question
1st Make sure the compound is ionic !!
2nd Identify the and name the cation
Metal that forms only one type of cation.
Metal that forms more than one type of cation.
3rd Identify and name the anion
Non-metals that form simple anions
4th Combine cation and anion names.
Ionic Compounds
Ionic Compounds
4
Cations
Metals whose ions can have
more than one possible charge
Metals with Invariant Charge
Metals with Variable
Charges
Groups 1A+1 & 2A+2,
Al+3, Ag+1, Zn+2, Sc+3
determine charge by
charge on anion
Ionic Compounds
Anions
Ionic Compounds
Polyatomic Anions
Polyatomic ions consist of
two or more atoms,
covalently bonded together,
that carry an overall charge
(usually negative)
Simple Anions
Recognized as single, nonmetals in an ionic
compound.
Ionic Compounds
Ionic Compounds
5
Name the following compounds
Polyatomic Ions and Oxyanions
-Seldomly carry the suffix “ide” (Exceptions are OH-1 and CN-1)
- Often end in “ite” or “ate” and have prefixes “hypo” or “per”
- The names of oxygen polyatomics (often called oxoanions)
are related to the number of oxygen atoms in the ion.
1.NaF
2.Au2S3
3.PbBr2
4.Na2SO4
5.Fe(ClO3)2
Formula
# of oxygens
Name
6.NH4Cl
ClO-1
hypochlorite
7.PCl5
ClO2-1
chlorite
ClO3-1
chlorate
ClO4-1
perchlorate
Ionic Compounds
All common oxyanions of Cl, Br and I carry a charge of -1
Some series of oxoanions also contain varying numbers
of H atoms and are named accordingly.
Ionic Compounds
Hydrates
„
„
„
‰
„
- The prefix thio indicates that a
sulfur atom has replaced in oxygen
atom.
No. of
Waters
hemi
½
mono
1
di
2
tri
3
tetra
4
penta
5
hexa
6
Anhydrous hepta
CoCl2
7
CoCl2·6H2O
in name attached waters indicated by suffix hydrate after name of ionic compound
‰
‰
CoCl2·6H2O = cobalt(II) chloride hexahydrate
CaSO4·½H2O = calcium sulfate hemihydrate
Hydrate
CoCl2·6H2O
Ionic Compounds
Prefix
hydrates are ionic compounds containing a
specific number of waters for each formula
unit
water of hydration often “driven off” by
heating
in formula, attached waters follow ·
octa
8
Ionic Compounds
6
Molecular Compounds
1st Make sure the compound is a molecular compound
2nd Write the name of first element in formula
3rd Write the name of the second element in the formula with an
-ide suffix
Number
Greek Prefix
1
Mono
2
Di
3
Tri
4
Tetra
5
Penta
6
Hexa
Formula
4th Use a prefix in front of each name to indicate the number of atoms
Use a prefix in front of each name to indicate the number of atoms
Common name
H2O
Water
NH3
Ammonia
H2O2
Hydrogen peroxide
Molecular Compounds
Binary Acids
Molecular Compounds
Examples
-Acids are species that produce hydrogen ions when dissolved in
water
Example :
HCl(aq)
H+(aq) + Cl-(aq)
-Binary acids have the general formula HaX
-(aq) stands for aqueous (Latin for dissolved in water)
-Because binary acids are so important we wish to emphasize
their acidity with special names.
HF (aq)
HCl (aq)
HF
HCl
-Use the Greek prefix hydro
HBr (aq)
HBr
-Follow with the name of the other non-metal using the suffix “ic”
HI (aq)
HI
Molecular Compounds
Molecular Compounds
7
Oxyacids
Acid Formulas from Names
- Contain three different elements (one being hydrogen, one
being oxygen and the third another non-metal)
- Basically the same rules used for oxyanions…except….
- The suffix “ous” is used in place of “ite” and…
- The suffix “ic” is used in place of “ate”
Examples of oxyacids and their names
Formula
Oxyanion
of salt
Name of salt
Formula
of acid
ClO-1
NaClO
HClO
ClO2-1
NaClO2
HClO2
ClO3-1
NaClO3
HClO3
ClO4-1
NaClO4
HClO4
„when
„write
name ends in acid, formulas starts with H
formulas as if ionic, even though it is molecular
„hydro prefix means it is binary acid, no
prefix means it is an oxyacid
Name of acid
„for oxyacid, if ending is –ic, polyatomic ion ends
in –ate; if ending is –ous, polyatomic ion ends in
–ous
Molecular Compounds
Molecular Compounds
Formula Mass and the Mole Concept
Formula mass – the mass of a formula unit in atomic
mass units. Applies to molecular and ionic compounds
One Mole of a compound – contains 6.022 x 1023
formula units (or molecular units for a molecular
compound).
•also known as molecular mass or molecular weight
Molar Mass – mass of one mole of a compound.
Numerically equivalent to the formula mass but with
units of g/mol !
The Mole Concept
The Mole Concept
8
Chemical Composition
A molecular formula tells how many moles of an
atom are in one mole of a molecular compound
a) How many moles of ethylene glycol are in 25.00mg of
ethylene glycol ?
b) How many moles of carbon are in the above sample ?
c) How many atoms of carbon are in the above sample ?
Molecular Formula – C2H6O2
1 mole of C2H6O2
Chemical Composition
Percent Composition
The Mole Concept
Percent Composition
Chemical formula
Percent Composition
The molecular formula for THC (the active ingredient in
marijuana) is C21H30O2. Calculate the percent mass of C,H,O.
Chemical Composition
Chemical Composition
9
Working Backwards
Percent Composition
Pretty easy (after some practise) to get the
percent composition from a known molecular
formula.
Chemical formula
An unknown compound is analyzed (see later) and determined to
be 57.84 % C, 3.64 % H and 38.52% O (by mass). Can you
determine the compound’s molecular formula ? See text 109-114.
For compound CxHyOz
x=
Can you work backwards to get the
molecular formula if you know the percent
composition ?
%C ⎛ M Cx H y Oz
⎜
100% ⎜⎝ M C
⎞
%H ⎛ M Cx H y Oz
⎟⎟ ; y =
⎜
100% ⎜⎝ M H
⎠
Chemical Composition
⎞
%O ⎛ M Cx H y Oz
⎟⎟ ; z =
⎜
100% ⎜⎝ M O
⎠
⎞
⎟⎟
⎠
Chemical Composition
Combustion Analysis
How percent composition is determined experimentally
Smallest coefficient
Divide equations (1), (2) and (3) by equation (3)
CxHyOz = C4H3O
The result is the empirical formula
Chemical Composition
Chemical Composition
10
Chemical Reactions
Some Examples to Try
1)
Diethyl ether is a carbon-hydrogen-oxygen compound.
The mass percent of carbon, hydrogen and oxygen are
64.82%, 13.60% and 21.58% respectively. What is its
empirical formula ?
2)
„Reactions
involve chemical changes in matter resulting in
new substances
„Reactions
involve rearrangement and exchange of
atoms to produce new molecules
Reactants
→
Products
3)
Chemical Composition
Chemical Reactions
Shorthand way of describing a reaction
„
Provides information about the reaction
methane gas burns to produce carbon dioxide
gas and gaseous water
‰
Formulas of reactants and products
whenever something burns it combines with O2(g)
CH4(g) + O2(g) → CO2(g) + H2O(g)
States of reactants and products
Relative numbers of reactant and product
molecules that are required
Can be used to determine weights of reactants used and
products that can be made
„
to show the reaction obeys the Law of
Conservation of Mass, it must be balanced
CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g)
symbols used to indicate state after chemical
(g) = gas; (l) = liquid; (s) = solid
(aq) = aqueous = dissolved in water
Chemical Reactions
Chemical Reactions
11
Rules for Balancing Chemical Equations
- You can only change the coefficients.
- You can NOT add new atoms or molecules into
the equation (doesn’t apply to REDOX reactions –
see later).
- You can NOT change the chemical formulas to
force a balanced equation.
- Usually done by trial and error (see page 115 for
a strategy if you find this tricky at first)
Solid cobalt (III) oxide reacts with elemental carbon to produce cobalt and
carbon dioxide.
Write a skeletal
equation
Balance atoms in
complex substances
first
Balance free elements
by adjusting coefficient
in front of free element
If fractional coefficients,
multiply through by
denominator
Check
Chemical Reactions
CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g)
„
„
„
CH4 and O2 are the reactants, and CO2 and H2O
are the products
the (g) after the formulas tells us the state of the
chemical
the number in front of each substance tells us the
numbers of those molecules in the reaction
‰
„
Example Questions
Name the following compounds
1. NiCl3
a) Nitrogen iodotrichloride
b) Nickel chloride
c) Nickel trichloride
d) Nickel(III) chloride
called the coefficients
this equation is balanced, meaning that there are
equal numbers of atoms of each element on the
reactant and product sides
‰
Chemical Reactions
to obtain the number of atoms of an element, multiply the
subscript by the coefficient
2. ClO2
a) Chlorine dioxide
b) Chloro oxygen
c) Chloro dioxygen
d) Chlorite
Chemical Reactions
12
What is the correct formula for Iron(III) sulfate ?
3. HF
a) Hydrofluoric acid
b) Hydrogen fluoride
c) Monohydrogen fluoride
d) Monohydrogen monofluoride
a) Fe3(SO4)3
b) Fe3(SO4)2
c) Fe2(SO4)2
4. Ca(H2PO4)2
a) Calcium phosphate
d) Fe2(SO4)3
b) Calcium(II) phosphate
c) Calcium dihydrogen phosphate
d) Calcium(II) dihydrogen phosphate
What is Expected ?
1) Match names with symbols for the first 36 elements
(e.x. I shouldn’t have to tell you that As = Arsenic)
3) Know the names and oxidation states of simple ions
(ex. Table 3.1), polyatomic ions (Table 3.3) and oxyacids
4) Give the names and formulas of inorganic compounds
(i.e. all naming rules covered in Chapter 3)
13