Transcript Introduction To Chemistry 30 - Prairie Spirit School Division

INTRODUCTION
TO CHEMISTRY 30
COMPONENTS OF AN ATOM The modern atom as viewed by scientists today consists of three main
particles located in two regions.
 The first of these two regions is the nucleus, or central core of the
atom which is composed of positively charged protons and
neutrons with a neutral charge.
ATOM REVIEW
 It is believed that the neutrons are needed to hold the positively charged protons
together in the nucleus. The force that holds these particles together is termed the
nuclear binding force and it is believed to be one of the strongest forces that exists
in nature.
 The nucleus takes up a very small portion of the atom. If the atom was the size of a
football field the nucleus would be the size of a household fly on the 55 yard line.
 The second region surrounds the nucleus and is termed an electron cloud. The cloud
holds the third particle which is a negatively charged electron.
CHARACTERISTICS OF THE ATOM
 The number of protons in the nucleus of an atom is termed its atomic
number. This number is distinctive (characteristics) for the atoms of
each element (it can be found on the periodic table).
 Atomic Number = # of protons
 The number of neutrons in the nucleus of an atom is not distinctive and
may vary. This creates varieties of atoms we call isotopes. Isotopes are
atoms of the same element with different numbers of neutrons.
 Another characteristic of an atom of an element is it's atomic mass.
Protons and Neutrons have approximately the same mass, while
electrons have very little mass in comparison to either Protons or
Neutrons. The atomic mass is therefore determined from the number of
protons and neutrons. It is often called the mass number (#).
 Mass # (Atomic Mass) = # of Protons + # of Neutrons.
 Since atoms of an element always have the same number of
protons, isotopes are atoms of the same element with
different mass numbers.
 The number of electrons in a neutral atom (no charge) is equal to the
number of protons (atomic #). Atoms may either gain or lose electrons
during chemical interactions with other atoms. If they gain electrons
they become negatively charged, if they lose electrons they become
positively charged. We term these charged atoms ions.
ASSIGNMENT
 Components of the atom
NAMING COMPOUNDS
 Covalent compounds (contain nonmetal atoms combining with other nonmetal atoms)
 Electrons are shared between atoms
 To Name:
 The first atom is named in full
 The second atoms name is shortened and -ide added.
 The prefixes below are added to the first and second name to indicate
the number of atoms present in the compounds.
 The prefix mono is typically not placed on the first atoms name.
HYDROCARBONS (STRAIGHT
CHAINED)
 Hydrocarbons are compounds that contain only carbon and hydrogen.
(CnH2n)
 To Name:
 The first part of the name is a prefix that indicates the number of carbon atoms. The
prefixes are the same as those used by Binary Molecular compounds above except
for the first four. These four are:
# of
Carbon
Atoms
1
2
3
4
Prefixes
meth eth prop but -
 The second part of the name is a suffix that describes if the compound
contains single bonds, a double or a triple bond between the carbon
atoms. The following table illustrates the naming and gives examples.
Group
Alkane
Alkene
Alkyne
Bonds between
carbons
all single
one double
one triple
Suffix
- ane
- ene
- yne
Ratio of Carbon
to Hydrogen
CnH2n+2
CnH2n
CnH2n-2
 Assignment: naming covalent compounds
 Ammonium (NH4 +) compounds
 Ammonium compounds contain the complex cation NH4
 To Name: (using a table of ions)
 The first part of the name is Ammonium
 Second part of name is the name of the anion.
Formula
Name
(NH4)2SO4
Ammonium sulfate
(NH4)3PO4
Ammonium phosphate
+1.
MONOVALENT IONIC CATIONS
 Ionic compounds containing monovalent cations (cation with one
charge)
 To Name (using a table of ions):
 Locate the name of the metal cation (positive ion). Make sure it has
only one charge.
 Locate the name of the anion.
 Place names together.
Formula
Name
AgCl
Silver chloride
Mg(NO3)2
Magnesium nitrate
DIVALENT CATIONS
 Ionic compounds containing divalent cations (metal ions with two
possible charges)
 To Name using given the formula:
 Locate the name of the anion and cation in a table of ions or periodic table.
 Using the concept that the total charge of the anion and cation must be equal we
can determine what the charge on the cation must be (anion charges are always
fixed.) See example below
Formula
Fe2O3
Charge on Total charge Total charge
Anion
on anion
on Cation
O 2-
Number of
Cations
2
Charge on Each
Cation
EXAMPLES
 Find the charges on the cations:
 FeO-
NiF2
 To determine name then we:
 Name the cation
 Determine the charge on the cation using the method above.
 Apply the correct Roman Numerals
 Finally name of the anion
Formula
Total
Name of
Total charge Charge on
Charge on
Cation
on Cation
Cation
Anion
Name
Cu2O
Copper
-2
+2
+1
Copper (I) oxide
CrCl3
Chromiu
m
-3
+3
+3
Chromium (III)
chloride
EXAMPLES
 TiC-
 Assignment: naming ionic compounds
PbO2-
MOLE THEORY
 Definition: The mole is defined as the atomic or molecular weight of a
substance expressed in grams. It is a metric unit for amount of
substance and has the abbreviation mol
 One mole of a substance then is the atomic weight of the
element expressed in grams.
 The number of particles in this amount is termed Avogadro's
Number and has been estimated at
6.023* 10 23 particles.
 Whenever we have Avogadro's number of particles in a sample we have
one mole.
 To give you a sense of it's size, imagine that each particle in a mole was
a piece of paper. If we were to stack this paper one sheet on top of
another, a mole of paper would stretch from the surface of the earth to
the planet Pluto
GRAM MOLECULAR WEIGHT
(MOLAR MASS)
 To calculate the gram molecular weight of a substance made up of more
than one element (compound), we add up the atomic weights of the
elements that comprised the compound. Atomic weights are listed in
the periodic table.
 Example: NaCl

Number of
Atoms
Na
1
Cl
1
Gram Molecular weight (
Molar Mass ) ; 1 mole =
Element
Atomic Weight
Total weight (g/mol)
(g/mol)
22.99
22.99
35.45
35.45
58.44 g/mol
Example: CH4
Element
Number of
Atoms
Atomic Weight
(g/mol)
Total weight
(g/mol)
C
1
12.01
12.01
H
4
1.01
4.04
Molar Mass =
16.05 g/mol
 Example Ca(NO3)2
Number of
Atomic Weight
Atoms
Ca
1
40.08
N
2
14.01
O
6
16.00
Gram Molecular weight ( Molar Mass ) ; 1
mole =
Element
 Assignment: Molar Mass sheet
Total weight
40.08
28.02
96.00
166.10 g
CALCULATIONS WITH THE MOLE
 The mole has three values that can be used to do calculations with the
mole. They are:
 mass
 volume (one mole in the gas state at 0 C and 100 kPa.(called standard
temperature and pressure STP = 24.5 L.)
 # of particles
STEPS:

 Write down the given information.
 Write down what you are trying to find.
 Use the mole triangle to determine what operation you will perform.
 Complete all required calculations and write down the final answer- **be sure to include
units**
EXAMPLES
 1. Calculate the mass in grams of 35 moles of CaCO3.
 Given information is 35 moles of CaCO3.
 Asked to calculate the mass in grams.
 The mole triangle indicates that you should multiply the 35 moles by
the molar mass of CaCO3
Step 1; Calculation of molar mass
1 * 40.08 g/mole = 40.08 g
1 * 12.01 g/mole = 12.01 g
3 * 16.00 g/mole = 48.00 g
1 mole = 100.09 g/mole
Step 2; Calculation of Answer
35 moles * 100.09 g/mol = 3503.15 g
 Calculate the # of molecules in 820 L of SO2 (g) given off by a chemical
plant at STP.
 The given information is 820 L of SO2 (g) at STP.
 Information you are asked to find is the # of particles.
 The mole triangle indicates that you should divide 820 L by the molar
volume to calculate moles
 then multiply the moles by 6.023 * 10
Step 1;Calculation of moles
820 L / 25.4 L/mol. = 32.28 mol.
23
p/mol.
Step 2; Calculation of Answer
32.28 mol. * 6.023 *10 23 p/mol. =
1.9 *10 24 particles
 Assignment: Mole Calculations
WORD AND FORMULA EQUATIONS
 1. Two types of equations are written by chemists:
 word equations: describe the substances that react in a chemical
reaction (termed reactants), and the products that are formed, along
with their states
 formula equations are a shorthand method used to describe the same
reactions. These are of two types:
 Skeleton equations: (unbalanced) which lists the correct formula of each reacting
substance and product substances, and their states.
 Balanced equations: which list the correct formulas, states and balances the
equation for the number of atoms present. That is it takes into account the Law of
Conservation of Mass, and makes sure there is the same number and type of atom in
the reactant and product. In Chemistry 30 we should only use balanced equations.
 We balance equations by changing the coefficients or numbers in front
of the substance.
 WE NEVER CHANGE THE FORMULAS OF SUBSTANCES
IN ORDER TO BALANCE.
 Counting the atoms correctly is therefore critical. The balance
(coefficient) we use is always multiplied by the subscripts used in each
formula, to indicate how many atoms are represented. If atoms are in
two different reactant or product compounds, they are added together
to determine how many are present in total.
DETERMINE THE # OF ATOMS OF
EACH TYPE PRESENT IN THE
FOLLOWING REACTANTS.
Reactants
# of each atom
Pb =
PbS + 2 PbO
S=
O=
Ca =
N=
Ca(NO3)2 + 2 KOH
O=
K=
H=
N=
2 NH4NO3 + H2S
H=
O=
S=
Fe =
N=
Fe(NO3)3 + 3 LiOH
O=
Li =
H=
Ca =
P=
Ca3(PO4)2 + 3 H2SO4
O=
H=
S=
BALANCING
 Balancing equations is basically a process of trial and error, called
inspection, but a few hints can help.
 1. Balance atoms that appear only once in reactant and product first, and
atoms that appear more than once last.
 Example #1:
Reactant
Product
___C3H8 (g)+ ___O2 (g)
___CO2 (g) + ___H2O (g)
Step Balance atoms that appear only once first (C
1
and H )
_1_C3H8 (g)+ ___O2 (g)
Step Balance atoms that appear more than once last
2
(O)
_1_C3H8 (g)+ _5_O2 (g)
_3_CO2 (g) + _4_H2O (g)
_3_CO2 (g) + _4_H2O (g)
 Balance polyatomic ions as a group, for example SO4
2- ion. Caution: The
ion must remain the same in reactant and product.
 Example #2:
Reactant
Product
___Ca(NO3)2 (aq) + ___Na3PO4 (aq)
___Ca3(PO4)2 (s) + ___NaNO3 (aq)
Step 1 Balance atoms that appear only once ( Ca , Na )
_3__Ca(NO3)2 (aq) + ___Na3PO4 (aq)
Step 2 Balance atoms in ions as groups (PO4 ; NO3 )
_3__Ca(NO3)2 (aq) + _2__Na3PO4 (aq)
___Ca3(PO4)2 (s) + _3__NaNO3 (aq)
_1__Ca3(PO4)2 (s) + _6__NaNO3
(aq)
 In some cases the # of atoms of an element in the reactants may be
odd, while the # in the products will always be even (due to a even
subscript). In this case you need to double the balance of all
atoms already balanced and continue the balancing.
 Example #3:
Reactant
___CuFeS2 (s) + ___O2 (g)
Step 1 Balance atoms that appear only once first
_1_CuFeS2 (s) + ___O2 (g)
Product
___Cu (s) + ___FeO (s) + ___SO2 (g)
_1_Cu (s) + _1_FeO (s) + _2_SO2 (g)
Step 2 Balance oxygen now. Notice that there is
five atoms in the products but the
reactants will always be even. To balance,
double all balances already made. Now
continue by balancing the oxygen
_2_CuFeS2 (s) + _5_O2 (g)
_2_Cu (s) + _2_FeO (s) + _4_SO2 (g)
 Assignment: Balancing equations worksheet
STOICHIOMETRY
 Chemical reactions are like the recipe for the cookies. The
balances in the equations are mole recipes that tell us the # of moles
that react and form.
 Example:
Equation (balanced)
If we had 2 moles of C3H8 (g)
then
_1_C3H8
_5_O2
+
(g)
(g)
_3_CO2 _4_H2O
+
(g)
(l)
2 moles
6 moles
10 moles
8 moles
 Notice that all of the values in the table are in the same ratio as the
balance in the equation. C3H8 : O2 is always 1 : 5, CO2 : H2O is always 3:
4 . We call these ratios, equation factors or mole ratio. The
reactants and products in this equation always react and form in these
Moles of ------>
C3H8 (g)
O2 (g)
CO2 (g)
H2O (l)
12 moles
2 moles
Complete the rest of this table using the
equation above
0.5 moles
5 moles
MOLE TO MOLE STOICHIOMETRY
 The following technique can be used to predict the # of moles that will
react or form in an equation.
 Identify the given number of moles.
 Identify the balance of the Given.
 Identify the balance of the substance you wish to find
 Multiply.
Moles of Known (n)
X
Balance of Unknown
Balance of Known
=
Moles of unknown (n)
 Example:
 Using the balanced equation below, predict
 1. The number of moles of C3H8 (g) that reacts to produce 8.4 moles of
CO2 (g).
Equation (balanced)
8.4 moles of C3H8 (g)
_1_C3H8 (g) + _5_O2 (g)
X
3 CO
1 C3H8
=
_3_CO2
_4_H2O
+
(g)
(l)
25.2 moles CO2 (g)
 The number of moles of H2O (l) that form if 63.7 moles of O2 reacts.
 Answer:
63.7 moles O2 (g)
X
4 H2O (l)
5 O2 (g)
=
51.0 moles H2O
(l)
 Assignment: Mole to Mole stoichometry
MASS TO MASS
 We can use a simple 3 step method to solve stoichiometric questions
with balanced equations.
 Identify the given and convert it to moles.
 Identify the desired, and multiply the given number of moles by the mole ratio to
produce moles of desired substance.
 Convert moles of desired substance to the units asked for in the question.
 Example:
 What mass of methane gas in grams must burn to produce 365
grams of water, by the following chemical reactions ?
_1_CH4(g)
+
_2_O2(g)
_2_H2O (g)
+
_1_CO2(g)
 Given is 365 g of water. Calculate moles of water.
365 g ÷18.02 g/mol
=
20.25 mol
 Identify desired; mass of Methane gas. Multiple by mole ratio
20.25 mol H2O (l)
X
1 CH4 (g)
2 H2O (g)
=
10.13 mol CO2 (g)
 Convert moles of desired to the units asked for in the question: Mass
of Methane gas.
10.13 mol CO2 X 44.01 g/mol
= 446 g
 Assignment: Mass to Mass Stoichiometry