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UNIT 1
Chemical Reactions
Part I
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.
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.
The outermost shell is called the valence shell. The electrons in the valence
shell are called the valence electrons.
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*
Ionic Compounds
An ion is a charged particle. An ion is formed when a neutral atom gains or
loses electrons. Positively charged ions are called cations, and negatively
charged ions are called anions.
*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.
Ionic compounds are usually made of metal and non-metal ions.
Example:
m nm
NaCl – sodium chloride
m nm
Fe2O3 – iron oxide
CuSO4 – copper sulfate
Ca3(PO4)2 – calcium phosphate
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
Naming Binary Ionic Formula
A binary compound contains 2 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
non-metal ion. Metal ions have positive charges and non-metal ions have
negative charges.
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 ____________________________.
Writing Binary Ionic Formula
The following must occur when writing the formula for ionic compounds.
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.
The "Criss-Cross" Method
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+
F1-
BaF2
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.
*Complete Ionic Compound Worksheet*
Polyatomic Ions
Some ions are composed of several atoms joined covalently. These are called
polyatomic ions (poly = many).
Refer to the Periodic Chart of 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(CH3COO)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 Polyatomic Compound Worksheet*
Stock Naming System
Several 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
Stock Naming
Writing the Chemical Formula
Example:
Write the formula for iron (III) chloride
Step 1: Write out the ions.
Fe3+ and ClStep 2: Criss-cross the charges.
FeCl3
Example:
Write the formula for lead (IV) sulfide.
Step 1: Write the ions.
Pb4+ and S2Pb2S4
*divide by GCF*
Pb2S4 ÷ 2  PbS2
Writing the Chemical Name
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.
Example:
Write the name for CoBr2.
CoBr2
 Each Br is 1-  total charge of 2To make it neutral, Co has to be 2+
Cobalt (II) bromide
Example:
Write the name for MnO2.
MnO2
 Each O is 2-  total charge of 4To make it neutral, Mn has to be 4+
Manganese (IV) oxide
*complete Stock Naming System Worksheet*
Covalent Compounds
Naming Covalent Compounds
Non-metals tend to combine chemically by sharing electron pairs. These bonds
are known as covalent bonds. Neutral compounds made of atoms joined
covalently are called molecular or covalent compounds.
We name covalent compounds differently than ionic compounds. We must
indicate the number of each element by adding a prefix in front of the
element's name.
Subscript
Prefix
Subscript
Prefix
one
mono
six
hexa
two
di
seven
hepta
three
tri
eight
octa
four
tetra
nine
nona
five
penta
ten
deca
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.
dinitrogen tetraoxide
Example:
Write the name for PCl5.
phosphorus pentachloride
Note: There are several exceptions to the naming rules. Here are the common
names for some of the compounds:
H2O = water
NH3 = ammonia
CH4 = methane
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.
N2O
Example:
Write the formula for sulphur hexafluoride.
SF6
Example:
Write the formula for phosphorus tribromide.
PBr3
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
QUIZ ON TUESDAY ON NAMING AND FORMULA WRITING
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.
2 KClO3 + heat  2 KCl + 3 O2
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:
SSymbo
l
+

(s)
(l)
(g)
(aq)
Meaning
and, reacts with, combines with, separates 2 or more reactants
yields, forms, makes, produces, separates reactants and products
solid state, precipitate, insoluble
liquid state
gaseous state, vapour
aqueous state (in water), dissolved in, soluble, in solution
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.
General Formula:
hydrocarbon + O2  CO2 + H2O
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.
General Formula:
A + B  AB
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.
General Formula:
AB  A + B
Example:
Solid nickel (II) hydroxide decomposes to produce solid nickel (II) oxide
and water.
Ni(OH)2 (s)  NiO (s) + H2O (l)
Single Displacement (Replacement) Reactions
Are chemical changes that involve an element and a compound as reactants.
General Formula:
A + BC  B + AC
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 (Replacement) Reactions
Occur when elements in different compounds displace each other or exchange
places. Generally, the reaction occurs in an aqueous system.
General Formula:
AB + CD  AD + CB
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.
General Formula:
ACID + BASE  WATER + 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)
Predicting Reaction Products
When determining what the products will be in a chemical reaction, use the
following information to help you.
Synthesis Reaction
Reactants: Generally two elements or two compounds (where at least one
compound is a molecular compound).
Probable Products: A single compound
Decomposition Reaction
Reactants: Generally a single binary compound or a compound with a polyatomic
ion.
Probable Products: Two elements (for a binary compound), or two or more
elements and/or compounds (for a compound with a polyatomic ion).
Combustion
Reactants: Oxygen and a compound of C, H, (O)
Probable Products: CO2 and H2O
Single Replacement Reaction
Reactants: An element and a compound
Probable Products: a different element and a new compound.
Double Replacement Reaction
Reactants: Two ionic compounds
Probable Products: Two new compounds
Determining the Physical States
To determine if a product is a solid or not, use a table of solubility. The
following are hints to help determine the physical state.
(s) – most metals, precipitates
(l) – mercury, bromine, water
(g) – noble gases, diatomic molecules (except bromine), ammonia
(aq) – substance is in a water based solution (use solubility chart)
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).
K
39
19
40
The symbol for potassium-40 would be: 1 9
The symbol for potassium-39 would be:
K
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
Molar Mass
Recall, Avogadro’s Number relates the number of particles to mass.
By definition, one mole of carbon atoms has a mass of 12.0000 g. If
the mass of one mole of any atom is its atomic mass in grams, then
one mole of aluminum atoms has a mass of 27.0 g
107.9
one mole of silver atoms has a mass of _____________
g
22.99
one mole of sodium atoms has a mass of ____________
g,
One mole of any compound has a mass equal to its formula/molecular
mass, in grams. Water has a molecular mass of 18.0 amu. The mass of
18.02
one mole of water molecules is ____________
g.
The mass of one mole of a substance is called the molar mass (M).
The units for molar mass are grams per mole (g/mol), so the molar
mass of water is 18.0 g/mol.