UNIT 1
Chemical Reactions
Part I
(Text: p. 276-327)
Write formulas and names for ionic, polyatomic and covalent compounds
using IUPAC nomenclature.
Write and classify balanced chemical equations from written
descriptions of reactions.
Predict the products of chemical reactions, given the reactants and
type of reaction.
Determine the average atomic mass using isotopes and their relative
abundance.
Research the importance and application of isotopes.
Describe the concept of the mole and its importance to measurement in
chemistry.
Calculate the molar mass of various substances.
Solve problems requiring conversions between moles, mass, and number
of particles.
Anatomy of an Atom
All atoms, except hydrogen, are made of 3 basic particles: protons, neutrons
and electrons. Each element has a unique number of protons, which is indicated
by its atomic number.
The outermost shell is called the ________________.
The electrons in the
valence shell
valence electrons
valence shell are called the _________________________
The atoms of elements in Period 1 have one shell. This shell contains a
2
maximum of ____
electrons.
2
The atoms of elements in Period 2 have _____
shells. The valence shell
8
contains a maximum of ______
electrons.
3
The atoms of elements in Period 3 have _____
shells. The valence shell
8
contains a maximum of ______
electrons.
*Complete Electron Shell handout*
Chemical Formulas
Chemistry has its own language. Chemists communicate in this language to
describe the millions of known compounds. This communication depends on a
standard system of naming and writing the formulas for compounds. Chemists
formed a group to standardize the system of naming and called themselves
the International Union of Physical and Applied Chemists, or IUPAC.
A chemical formula is a shorthand method to represent compounds that uses
the elements' symbols and subscripts. The chemical formula gives the
following information:
•The different elements in the compound.
•The number of atoms of each element in the compound.
element
symbols
•Subscript tells you amount of each element.
•Water contains:
H2O
•2 Hydrogen’s
•1 Oxygen
subscript
* No subscript indicates only 1 atom is present*
Ca3(PO4)2
•Contains 3 calcium atoms
*every subscript inside the brackets needs to be multiplied by 2*
P
1 atom x 2 = 2 phosphorus atoms
O
4 atoms x 2 = 8 oxygen atoms
Ionic Compounds
ion
An __________
is a charged particle. An ion is formed when a neutral atom
gains or loses electrons. Positively charged ions are called _____________,
cations
anions
and negatively charged ions are called ________________.
*Complete “Keeping an ION That” handout*
Ionic compounds are formed when two or more oppositely charged ions are
attracted to each other. This chemical attraction is called a chemical bond. An
ionic bond is formed when a negatively charged ion is attracted to a positively
charged ion. Ions combine together so that their charges add to zero.
metal and non-metal
Ionic compounds are usually made of _______________________
ions.
Example:
m nm
NaCl – sodium chloride
m nm
Fe2O3 – iron oxide
CuSO4 – copper sulfate
Ca3(PO4)2 – calcium phosphate
non-metals
metals
The periodic table arranges atoms according to their properties. The periodic
table below shows the names of several groups we will be referring to
throughout this course.
Writing Binary Ionic Formula
2
A binary compound contains ______
different kinds of elements. There can
be more than one atom of each element in a binary compound. Binary ionic
compounds usually contain one kind of metal ion combined with one kind of
positive
non-metal ion. Metal ions have ________________
charges and non-metal
ions have ________________
charges.
negative
When naming an ionic compound from its formula follow the rules below:
1. The cation (positive ion) is named first, followed by the anion
(negative ion).
2. Write the full name of the metallic element (positive ion).
3. Write the name of the non-metallic element (negative ion) and change
the ending to "-ide".
Example:
Write the name of NaCl.
Step 1: Name the first element.
Na = sodium
Step 2: Name the second element and change the ending to "-ide".
Cl = chlorine  chloride
sodium chloride
The name of the compound is ________________________.
Example:
Write the name of Mg3P2.
Step 1: Name the first element.
Mg = magnesium
Step 2: Name the root of the second element and add "-ide".
P = phosphorus  phosphide
magnesium phosphide
The name of the compound is ____________________________.
Naming Binary Ionic Formula
There are two methods for determining the formula of a compound, but the
following points must hold true:
1. The formula must have the cation first, followed by the anion.
2. The sum of the charges of the ions must be zero. That is, the number
of positive charges must equal the number of negative charges.
3. You may not change the charge of the ions to make the ion charges
equal
zero.
Method 1 – Lowest Common Multiple
1. Write the symbols for the ions involved.
2. Determine the lowest whole number ratio that will
give an overall net charge of zero. That is, the number of
positive charges must equal the number of negative
charges.
Example:
Write the formula for aluminum oxide.
Step 1: Write the ions and their charges.
Al3+ and O2Step 2: Determine the lowest common multiple.
•LCM for 3 and 2 is 6
•To get 6 positive, need 2 Al3+  2 x 3+ = 6+
•To get 6 negative, need 3 O2-  3 x 2- = 6-
becomes subscript
Al2O3
The formula for aluminum oxide is ___________________.
Method 2 – The "Criss-Cross" Method
This method accomplishes the same as the lowest common multiple methodthe total charge of the compound is zero.
1.
Write the ions and their charges side by side.
2.
Make the number of the charge of one ion the subscript of the
other
ion (omitting the + or – sign). Remember we do not write the
number
one as a subscript.
3.
Reduce all subscripts to their simplest form, if necessary.
Example:
Write the formula for aluminum oxide.
Step 1: Write the ions and their charges.
Al3+ and O2-
Step 2: Make the number of the charge of one ion the subscript of the other ion.
Al3+
O2-
Al2O3
Example:
Write the formula for barium fluoride.
Ba2+
F1BaF2
Note: The charge on the fluoride ion is 1–. Since IUPAC rules do not write the
number one as a subscript, we leave the barium without a subscript.
Polyatomic Ions
Some ions are composed of several atoms joined covalently. These are called
polyatomic ions (poly = many).
Refer to the Table of Common Polyatomic Ions for a list of ions.
The charge for polyatomic ions is for the whole group of atoms not just for
the atom written last. DO NOT change the subscripts of polyatomic ions; if
you change the subscripts you change the identity of these ions.
When indicating the presence of more than one polyatomic ion in a compound,
we use parenthesis around the polyatomic ion, followed by its subscript. For
example, the compound Al(C2H3O2)3 has an aluminum ion and 3 acetate ions.
Placing the acetate ion in parenthesis and following it with the subscript 3
indicates there are 3 acetate ions.
Example:
Write the name for KNO3.
Step 1: Identify the cation.
K+  potassium ion
Step 2: Identify the anion.
NO3-  nitrate ion
Step 3: Write the name of the cation first, followed by the anion.
potassium nitrate
Example:
Write the name of Hg2Cl2.
Step 1: Identify the cation.
Hg22+  dimercury ion
Step 2: Identify the anion.
Cl-  chloride ion
Step 3: Write the name of the cation first, followed by the anion.
dimercury chloride
Example:
Write the name of Na3PO4.
Step 1: Identify the cation.
Na+  sodium ion
Step 2: Identify the anion.
PO43-  phosphate ion
Step 3: Write the name of the cation first, followed by the anion.
sodium phosphate
Example:
Write the name of NH4SCN.
Step 1: Identify the cation.
NH4+  ammonium ion
Step 2: Identify the anion.
SCN-  thiocyanate ion
Step 3: Write the name of the cation first, followed by the anion.
ammonium thiocyanate
*Complete Ionic Compound Worksheet*
Stock Naming System
Most of the transition metals have more than one possible ion charge. They
are often referred to as being multivalent. For example,
Ion
Possible Ion Charges
Copper
1+, 2+
Iron
2+, 3+
Cobalt
2+, 3+
Chromium
2+, 3+
Lead
2+, 4+
Tin
2+, 4+
In 1919, Alfred Stock (1876 – 1946), a German chemist, suggested using
numbers to indicate the charge of the ions. Prior to this the ions were given
different names based upon their charge. The Cu+ ion was called cuprous and
the Cu2+ ion was called cupric. However, the Fe2+ ion was ferrous and the Fe3+
ion was ferric. Since the charges were not always the same, the "–ic" and "–
ous" suffixes caused some confusion. Today, the Stock naming system uses
Roman numerals following the metal ion's name to indicate the ion's charge.
Example:
Copper (I) = Cu+ cuprous
Copper (II) = Cu2+ cupric
Iron (II) = Fe2+ ferrous
Iron (III) = Fe3+ ferric
As a general rule, all metals are multivalent (have more than one ion charge)
except group one and two metals, silver, cadmium, zinc, and aluminum. Unless
the metal is one of these use the Roman numeral.
Multivalent Compounds
Example:
Write the formula for iron (III) chloride
Step 1: Write out the ions.
Fe3+ and ClStep 2: Balance or “criss-cross” the charges.
FeCl3
Example:
Write the formula for lead (IV) sulfide.
Step 1: Write the ions.
Pb4+ and S2Step 2: Balance or “criss-cross” the charges.
Pb2S4
Step 3: Reduce the subscripts.
*divide by GCF*
Pb2S
2  PbS2
Naming Multivalent Compounds
We name in a very similar manner as those ions with a single ion charge, except
we must determine the charge on the metal ion.
To determine the charge on the metal ion,
1. Write the name of the ions.
2. Multiply the charge of the anion by its subscript.
3. Divide this number by the subscript of the metal ion. The result is the
charge on the metal ion.
Example:
Write the name for CoBr2.
Step 1: Write the names of the ions. (including the charge of the anion)
cobalt
bromide
Cox
Br1-
Step 2: Multiply the charge of the bromide by its subscript then divide by the
subscript for cobalt.
1 x 2 = 2 1 = 2
*ignore charge*
charge for cobalt
Step 3: Write the name, indicating the charge of cobalt using roman numerals.
cobalt (II) bromide
Example:
Write the name for MnO2.
Step 1: Write the names of the ions.
manganese
oxide
Mnx
O2-
Step 2: Multiply the charge of the oxide by its subscript then divide by the
subscript for manganese.
2 x 2 = 4 1 = 4
charge for manganese
Step 3: Write the name.
manganese (IV) oxide
*complete Multivalent Worksheet*
Naming Covalent Compounds
Example:
Write the name for CO2.
Step 1: Name the first atom with prefixes.
There is only 1 carbon. We omit “mono” for the first element.
carbon
Step 2: Name the second element using prefixes and end in "-ide".
There are 2 oxygen's, so we use the di prefix
dioxide
Step 3: Write the name of the compound writing the substance found more to the
left on the periodic table first.
carbon dioxide
Example:
Write the name for N2O4.
Step 1: Name the first atom with prefixes.
dinitrogen
Step 2: Name the second element using prefixes and end in "-ide".
tetraoxide
Step 3: Write the name of the compound.
dinitrogen tetraoxide
Writing Covalent Compound Formulas
Writing formulas for covalent compounds involves the following rules:
1. Write the symbol for the first element followed by the subscript indicated
by the prefix.
2. Write the symbol of the second element followed by the subscript
indicated by its prefix.
DO NOT REDUCE THE SUBSCRIPTS!!!
Example:
Write the formula for dinitrogen monoxide.
Step 1: Write the symbol and subscript for the first element.
dinitrogen  N2
Step 2: Write the symbol and subscript for the second element.
* 1 as a subscript is not needed *
monoxide  O
Step 3: Combine
N2O
Example:
Write the formula for sulphur hexafluoride.
SF6
Diatomic Molecules
Some elements do not exist as single atoms. These elements exist as pairs of
atoms joined covalently, called diatomic molecules. The elements that exist as
diatomic molecules are hydrogen (H2), oxygen (O2), fluorine (F2), chlorine (Cl2),
bromine (Br2), iodine (I2) and nitrogen (N2).
When oxygen gas, hydrogen gas, etc. is used the formula will be O2, H2, etc.
Here is a mnemonic device to help you remember the diatomic molecules:
I Have No Bright Or Clever Friends
I = iodine
H = hydrogen
N = nitrogen
Br = bromine
O= oxygen
Cl = chlorine
F = fluorine
* Complete Covalent Compound Worksheet *
Chemical Equations
A chemical equation indicates the substances reacting and the substances
produced in a chemical reaction. A chemical equation also shows the ratio in
which these substances react or are produced.
A word equation can describe a chemical reaction.
Example:
Hydrogen gas and oxygen gas react to form (or yield) water vapour.
2 H2(g) + O2(g)  2 H2O(g)
A chemical equation can also show heat changes that occur.
Endothermic reactions cause the reaction vessel to feel cooler because the
reaction absorbs energy. The energy is used in the reaction, so energy is a
reactant.
Exothermic reactions release energy. Consequently, we consider heat or
energy to be a product of an exothermic reaction.
2 H2(g) + O2(g)  2 H2O(g) + energy
Recall:
Symbol
+

Meaning
and, reacts with, separates 2 or more reactants
yields, forms, separates reactants and products
(s)
solid state
(l)
liquid state
(g)
gaseous state
(aq)
aqueous state (in water)
Balancing Chemical Equations
Example:
Balance the equation
C3H8 +
O2 
CO2 +
H 2O
* See white board*
Example:
Balance the equation
Al2(SO4)3 +
CaCl2 
AlCl3 +
* See white board*
* Complete Balancing Chemical Equations Worksheet*
CaSO4
Types of Chemical Reactions
Combustion Reactions
Are very rapid reactions of a hydrocarbon (fuel) substance with oxygen gas
producing carbon dioxide and water plus a lot of heat.
Example:
CH4(g) (methane) + 2 O2(g) 
CO2(g) + 2 H2O(g)
Synthesis Reactions
Involve the combining of smaller atoms/molecules into larger, more complex
molecules. If only two different atoms appear on the reactant side, then the
reaction must be synthesis.
Example:
Water and dinitrogen pentoxide gas react to produce aqueous hydrogen nitrate.
H2O (l) + N2O5 (g)  2 HNO3 (aq)
Decomposition Reactions
Involve the splitting of large molecules into smaller molecules or elements.
Example:
Solid nickel (II) hydroxide decomposes to produce solid nickel (II) oxide
and water.
Ni(OH)2 (s)  NiO (s) + H2O (l)
Single Displacement Reactions
Are chemical changes that involve an element and a compound as reactants.
Example:
Fluorine gas will react with sodium bromide in an aqueous solution to produce
sodium fluoride and liquid bromine.
F2 (g) + 2 NaBr (aq)  2 NaF (aq) + Br2 (l)
switch
Double Displacement Reactions
Occur when elements in different compounds displace each other or exchange
places. Generally, the reaction occurs in an aqueous system.
Example:
When aqueous lithium iodide and aqueous silver nitrate react, they will produce
solid silver iodide and aqueous lithium nitrate.
LiI (aq) + AgNO3 (aq)  AgI (s) + LiNO3 (aq)
Acid-Base Reactions
When an acid and base react together, the reaction is known as a
neutralization reaction. The products will always be water and a salt.
Example:
When a solution of aqueous hydrochloric acid and solid potassium hydroxide
react, water and aqueous potassium chloride are formed.
acid
base
water
salt
HCl (aq) + KOH (s)  H2O (l) + KCl (aq)
Isotopes
The number of neutrons in each atom varies, even between atoms of the
same element. Potassium can exist as three different atoms. All three
atoms contain 19 protons, but one potassium atom has 20 neutrons, another
21 neutrons and yet another has 22 neutrons.
Atoms that have the same number of protons but differ in their number of
neutrons are called isotopes.
As you would expect, if different isotopes have different numbers of
neutrons, they will have different masses. The mass number of an atom is
the sum of the protons and neutrons found in the nucleus of that atom.
If we look at the potassium isotopes above, the isotope containing 19 protons
19 + 20 = 39 We call this isotope
and 20 neutrons will have a mass number of ___________.
potassium-39.
The isotope that has 19 protons and 21 neutrons will have a mass number of
___________
19 + 21 = 40 and is called potassium-40.
Chemists have designed a symbol for each isotope that includes the element’s
symbol, its atomic number (Z) and its mass number (A).
The symbol for potassium-39 would be:
K
39
19
K
40
The symbol for potassium-40 would be: 1 9
K
40
K
39
Atomic Mass
The masses of individual atoms are expressed as atomic mass units (amu) or
µ. The atomic mass unit is defined as 1/12 the mass of a carbon-12 atom. This
means a proton or a neutron has mass equal to approximately one atomic mass
unit.
In many cases the amount of each isotope in the sample, or its relative
abundance, can be determined using a mass spectrometer. The relative
abundance of an isotope is the percent of each isotope found in an average
sample of the element.
You have noticed that the atomic mass shown for each element on a periodic
table is rarely a whole number. This is because it is actually an average mass
of all isotopes of that element.
How to Calculate Average Atomic Mass
To determine the average atomic mass, you first need to determine what the
mass contribution is for the isotope.
mass contribution = (mass)(relative abundance)
Once all the mass contributions have been determined, you simply add up the
numbers to find your average atomic mass.
Example:
Find the atomic mass of magnesium, using the information provided.
Relative Abundance of Stable Magnesium Isotopes
Isotope
Relative Abundance (%)
Atomic Mass (amu)
Mg-24
78.70
23.98504
Mg-25
10.13
24.98584
Mg-26
11.17
25.98259