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Science 9 – Chemistry Unit
Table of Contents
Atomic Particle Review .....................................................................2
Symbols and Formulas .......................................................................3
Activity: Developing a Classification System for Elements .............4
Summary of some element family characteristics..............................6
Problems for Practice .........................................................................7
Electrons in Four Easy Steps .............................................................10
The History ............................................................................10
The Shells...............................................................................11
The Electron Behaviour .........................................................11
The Big Picture ......................................................................12
Step Diagram for the Shell Model .....................................................14
The Flame Test: Evidence for Electron Shells? ................................15
The Periodic Table of Elements .........................................................16
Ion Review .........................................................................................17
Balancing Chemical Equations ..........................................................23
Equation Balancing Questions ...........................................................25
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Science 9 – Chemistry Unit
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Symbols and Formulas
Berzelius, in 1813, simplified chemical symbols. He used letters to represent the atoms of each
element. Berzelius suggested that the first letter of the name of the element would make a suitable
symbol. Because there were more than 26 elements known, a problem arose immediately. Carbon,
cobalt, calcium, chlorine and copper could not all have the same symbol. To overcome this difficulty C
is used for carbon, Co for cobalt, Ca for calcium, Cl for chlorine and Cu for copper (Latin, cuprum).
Thus a chemical symbol is a capital letter, or capital letter followed by a small letter. In most cases the
letters are the first or the first and second letters of the name of the element. When this is not so, the
symbol has come from the name of the element in another language such as Latin. Remember that a
chemical symbol represents ONE atom of the element. Thus Cl represents one atom of the element
chlorine, Ag one atom of silver, and C one atom of carbon.
The symbols of the elements are used to show the composition of a molecule. A chemical
formula is made up of symbols placed side by side. Each symbol represents one atom of the element.
A formula represents a molecule of a compound. A formula shows the elements and the number of
atoms of each element in the molecule of a compound. A numeral is placed at the lower right hand
corner of the symbol to show the number of atoms of the element. If no numeral is placed there, then it
is understood that there is only one atom of that element in the molecule. Thus H2O shows that 2 atoms
of hydrogen are joined with one atom of oxygen to form 1 molecule of water.
Both compounds and elements have formulas. The formulas of compounds have two or more
different symbols. The formulas of elements have only one symbol.
Questions:
1.
a.
Define "chemical symbol".
b.
What does a chemical symbol represent?
2.
What do the following symbols represent?
Al, As, Cu, H, Pb, N, O, Sn, Zn.
3.
Write the chemical symbols for the following elements: antimony, barium, carbon, fluorine,
iron, magnesium, mercury, potassium, silicon, sodium, sulfur.
4.
a.
Define "chemical formula".
b.
What does a chemical formula represent?
5.
What is the composition of each of the following molecules? H2 (hydrogen gas), C2H2
(acetylene gas), O3 (ozone), Na2CO3 (washing soda), (NH4)2Cr2O7 (ammonium dicromate).
Activity: Developing a Classification System for the Elements
When two or more elements react (combine), they produce a new substance called a compound.
In every compound the atoms are bonded (joined together) in a certain way. A molecule of water
(formula - H2O) is made up of two atoms joined to one atom of oxygen. There are hundreds of
thousands of different compounds, each with its own particular combination of elements. Sugar is made
from the elements carbon, hydrogen, and oxygen. Table salt is made from the elements sodium and
chlorine.
Experiments during the last one hundred and fifty years have provided evidence that elements
can be organized into groups according to behaviour. Investigations like those you may have performed,
the work of Rutherford, and many other experiments have been used as evidence that the numbers of
protons or electrons in atoms might be the key to classifying elements into groups.
According to our model of the atom - a small positive nucleus surrounded by negatively charged
electrons - transfer of electric charge is a transfer of electrons from one atom to another. Some atoms
tend to lose electrons, while others tend to attract and keep electrons.
Your next problem will be to group elements according to their ability to gain or lose electrons.
In this way you may be able to predict which of the elements should combine to form compounds.
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Science 9 – Chemistry Unit
Table 1: Properties of some elements
Element
Symbol
Description
Atomic
Number
Aluminum
Argon
Beryllium
Boron
Calcium
Carbon
Chlorine
Fluorine
Helium
Hydrogen
Lithium
Magnesium
Neon
Nitrogen
Oxygen
Phosphorous
Potassium
Silicon
Sodium
Sulphur
Al
Ar
Be
B
Ca
C
Cl
F
He
H
Li
Mg
Ne
N
O
P
K
Si
Na
S
Silvery metal
Colourless gas
Silvery metal
Yellowish brown solid
White powdery solid
Black crystal
Yellow green gas
Pale yellow gas
Colourless gas
Colourless gas
Silvery metal
Silvery metal
Colourless gas
Colourless gas
Colourless gas
Red or yellow crystal
Silvery metal
Silvery crystal
Silvery metal
Yellow crystalAl
13
18
4
5
20
6
17
9
2
1
3
12
10
7
8
15
19
14
11
16
Number of
electrons readily
gained or lost.
3 lost
0 lost or gained
2 lost
3 lost
2 lost
4 lost or gained
1 gained
1 gained
0 lost or gained
1 lost
1 lost
2 lost
0 lost or gained
3 gained
2 gained
3 gained
1 lost
4 lost or gained
1 lost
2 gained
Procedure:
1.
Examine table 1 carefully. Obtain a set of paper squares of four different colour (your teacher
will tell you how many of each colour). Select one colour for elements that lose electrons,
another for elements that gain electrons, a third colour for elements that either gain or lose
electrons, and a fourth for elements that neither gain nor lose electrons. Use a separate paper
square for each element and record three pieces of information. At the top of the square, write
the number of electrons the element gains or loses. In the middle of the square write the atomic
symbol for the element. At the bottom of the square write its atomic number. For example, if
yellow is the colour chosen for elements that lose electrons, take a yellow square for aluminum.
The completed square should look like the diagram below. Make a separate square for each
element in the table of elements given.
number of electrons
3 gained or lost
Al
Atomic symbol
13
Atomic number
Aluminum
Element name
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Science 9 – Chemistry Unit
2.
3.
4.
Arrange the squares in a line according to atomic number (the number at the bottom of the
square). Start with atomic number 1 on the left and end with atomic number 20 on the right. In
your notebook, make a copy of the arrangement of squares.
Study the line of squares carefully. What pattern do you see in the numbers of electrons gained
and lost?
Make a new arrangement of the squares according to atomic number and the number of electrons
gained and lost. The new arrangement should have several rows instead of just one. Colours
will also help in making the new grouping. After your arrangement has been checked by your
teacher, copy it in your notebook.
Sample Questions:
1.
Pick an element that loses a certain number of electrons and another element that gains the same
number of electrons. What compound should form as a result of the combination of these two
elements?
2.
Which element would be not be likely to combine with anything?
3.
Compare the chart you prepared with the method of grouping that was originally used (i.e.
alphabetic). Which way of arranging elements is more useful - according to alphabetic order,
according to atomic number or according to appearance? Why?
Summary of some element family characteristics:
Name
Helium
Neon
Argon
Krypton
Xenon
Radon
Fluorine
Chlorine
Bromine
Iodine
Oxygen
Sulfur
Selenium
Tellurium
Polonium
Nitrogen
Phosphorus
Arsenic
Antimony
Bismuth
Carbon
Silicon
Germanium
Tin
Lead
Boron
Aluminum
Gallium
Indium
Thallium
Atomic Atomic
Symbol Number
He
Ne
Ar
Kr
Xe
Rn
F
Cl
Br
I
O
S
Se
Te
Po
N
P
As
Sb
Bi
C
Si
Ge
Sn
Pb
B
Al
Ga
In
Tl
2
10
18
36
54
86
9
17
35
53
8
16
34
52
84
7
15
33
51
83
6
14
32
50
82
5
13
31
49
81
Atomic
Weight
Number of electrons
per group
4.0
20.2
39.9
83.8
131.3
222.0
19.0
35.5
79.9
126.9
16.0
32.1
79.0
127.6
210.0
14.0
31.0
74.9
121.8
209.0
12.0
28.1
72.6
118.7
207.2
10.8
27.0
69.7
114.8
204.4
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
5
8
8
8
8
8
7
8
8
8
6
8
8
8
8
5
8
8
8
8
4
8
8
8
8
3
8
8
8
8
8
18 8
18 18 8
18 32 18
7
18 7
18 18
8
7
6
18 6
18 18 6
18 32 18
6
5
18 5
18 18 5
18 32 18
5
4
18 4
18 18 4
18 32 18
4
3
18 3
18 18 3
18 32 18
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Science 9 – Chemistry Unit
Beryllium
Magnesium
Calcium
Strontium
Barium
Radium
Be
Mg
Ca
Sr
Ba
Ra
4
12
20
38
56
88
9.1
24.3
40.1
87.6
137.4
226.0
2
2
2
2
2
2
2
8
8
8
8
8
2
8 2
18 8 2
18 18 8
18 32 18
2
8
2
Hydrogen
Lithium
Sodium
Potassium
Rubidium
Cesium
Francium
H
Li
Na
K
Rb
Cs
Fr
1
3
11
19
37
55
87
1.0
6.9
23.0
39.1
85.5
132.9
223.0
1
2
2
2
2
2
2
1
8
8
8
8
8
1
8 1
18 8 1
18 18 8
18 32 18
1
8
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Problems for Practice
Gases such as helium, neon, argon, which belong to the helium family, usually do not react
(combine) with each other or with other elements. Scientists believe that the electrons of these inert
gases offer an explanation for this lack of reactivity. Scientists also believe that the reactivity of other
elements depends upon the ease with which their atoms gain or lose electrons and achieve electron
groupings like those of inert gases.
Work each of the following problems to see how different elements may combine to form
compounds.
1.
Examine the beryllium family on the previous page. How might the electron grouping of
Calcium (Ca) be changed to resemble the electron grouping of argon (Ar)?
2.
Examine the oxygen family on the previous page. How might an atom of sulfur (S) gain an
electron grouping like that of argon (Ar)?
3.
Calcium (Ca) and sulfur (S) combine to form calcium sulfide (CaS). Review your answers to
problems 1 and 2 and explain how the combination of calcium and sulfur provides each with an
electron grouping like that of an inert gas.
4.
What is the electrical charge of a calcium atom before the reaction? Of a sulfur atom before the
reaction?
5.
What would be electrical charge of calcium after it lost two electrons? Of sulfur after it gained
two electrons?
Answers to Problems for Practice
1.
Calcium has two electrons in its outer regions. If it lost these two electrons, its (new) outer
region would have eight electrons. Calcium would then have the same electron grouping as that
of argon.
2.
An atom of sulfur has six electrons in its outer region (shell). If it gained two electrons, its outer
region would have eight electrons. Sulfur would then have the same electron grouping as argon.
3.
In this reaction, calcium loses two electrons to sulfur. Both then have an electron grouping like
argon, an inert gas.
4.
A calcium atom has twenty protons (positive charges) and twenty electrons (negative charges). It
is electrically neutral (zero charge). Sulfur has sixteen protons and sixteen electrons and is also
electrically neutral.
5.
Calcium would lose two negatively charged electrons and be left with a charge of +2. Sulfur
would gain two negatively charge electrons and be left with a charge of -2.
Calcium (Ca)
0
has a
neutral
it
loses
(-2)
two
negative
=
is
left
6
+2
a positive
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Science 9 – Chemistry Unit
charge
electrons
with
charge
(-2)
two
negative
electrons
=
is
left
with
-2
a negative
two
charge
Sulfur (S)
0
has a
neutral
charge
+
it
gains
Formula:
Ca+2
+
S-2
=
CaS (the charge of zero is understood)
Questions:
Members of the helium family (with rare exceptions) are not able to combine chemically with
other elements. Chemists believe this lack of reactivity has something to do with the structure of their
electron grouping.
1.
How would a sodium (Na) acquire an electron grouping like that of neon (Ne)?
2.
How would chlorine (Cl) acquire an electron grouping like that of neon? Like that of argon (Ar)?
3.
If an atom of sodium and an atom of chlorine are brought together, how might both atoms
achieve an electron grouping like that of an inert gas?
4.
How would this change affect the electrical charge of each atom (use the method for calculating
charge as shown above).
5.
Using symbols, write formulas for the compounds most likely to be produced from a reaction
between the following pairs of elements (usually the element that loses electrons is written first
in a formula for a compound):
a.
lithium and iodine
b.
sodium and bromine
c.
potassium and chlorine
d.
rubidium and fluorine
e.
cesium and bromine
6.
What would have to happen to an atom of oxygen to give it an electron grouping like that of
neon?
7.
How many atoms of each of the following elements would be needed to supply the electron
requirements of one oxygen atom?
a.
sodium
b.
cesium
c.
magnesium
d.
barium
8.
Frequently (as in Problem 7), chemical reactions require unequal numbers of atoms from the
combining elements. In written formulas for such combinations, the number of atoms included
from each element appears slightly below and to the right of each element's symbol. Where only
one atom is included, no number is written - it is understood. For example, you probably know
that the formula for water is H2O. The number 2 slightly below and to the right of H and the
absence of any number after O indicates that a molecule of water is formed from two atoms of
hydrogen and one atom of oxygen. Now look at a more complex example: the formula for an
aluminum oxide is Al2O3; this means that the combining ratio for aluminum oxide is two atoms
of aluminum (Al) to three atoms of oxygen. Now write the formula for the combination of
oxygen with each element listed in Problem 7.
9.
The atomic number of the element hydrogen is 1, and its average atomic weight is 1.008 Atomic
mass units.
a.
An atom of hydrogen has how many protons? How many neutrons? How many
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Science 9 – Chemistry Unit
b.
c.
electrons?
From its electron arrangement, to which family/ies might hydrogen belong?
What would be the formula for a combination of hydrogen and chlorine? of lithium and
hydrogen? of calcium and hydrogen?
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Science 9 – Chemistry Unit
ELECTRONS IN FOUR EASY STEPS
Figure 1: History of the Atomic Model
1. The History:
The concept of electrons in energy shells is not necessarily an easy one to grasp. A short history
of the development of a model for the atom shows that there were many theories along the way. The
Raison Bun Theory pictured the atom as a bun whose raisons represented electrons. The electrons were
just mixed in with the general "atomic" dough. This theory, however, did not do anything to explain
why atoms interacted. The next theory to come along was the Two-Dimensional Planetary Theory. This
model had the nucleus in the center of a series of concentric (common centered) circular orbits. It was
discredited because it only had matter existing in two dimensions. Everything would be flat!! The
Three-Dimensional Planetary Theory was then introduced. It explained matter's 3-D nature but did not
adequately explain why matter combined chemically. It also implied that the exact location and speeds
of the electrons could be determined. This was found, through experimentation, to be incorrect. In fact,
Heisenberg went so far as to state that "the exact location and speed of an electron could never be
known". Finally, the Electron Cloud or Electron Shell Model was introduced. What it said was that
electrons could be found in shells around the nucleus. Their exact positions and speeds could never be
determined but their approximate locations could be found based upon the energy which they were
thought to possess.
2. The Shells
The shells of which we speak are not physical, tangible shells. Instead they are zones where the
electrons are thought to possess certain amounts of energy. Like gravitational potential energy, this
amount of energy increases as the electron gets further from the nucleus. Therefore it "costs" more
energy to keep an electron in a distant shell than it does to keep it in an inside shell. When an atom's
electrons begin to fill shells, they start with those shells closest to the nucleus and work their way
outward.
The following graphic shows the order in which electrons fill the shells. The lowest steps of the graphic
fill first and then successively higher steps fill.
Figure 2: Energy Steps for Shell Model
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Science 9 – Chemistry Unit
The height of the steps indicates the relative amount of energy that it costs to stay in that
position. Notice that the L shell is further subdivided into subshells. Though the L shell has a capacity
of 8 electrons, it is divided into two subshells - one of which has a capacity of 2 electrons and the other
of which has a capacity of 6 electrons. However, we will not concern ourselves with these details for the
moment.
3. The Electron Behavior
The electrons of elements can be stable or unstable. Stability depends upon whether the outer
shell of the atom is full or not. Which is the outer shell? The outer shell is any outermost shell which
contains electrons. If one outer shell loses all of its electrons then the next closest shell to the nucleus
becomes the outer shell. Atoms will gain or lose electrons in order to fill their outer shells. When an
atom gains electrons it becomes a negative ion. If it loses electrons, it becomes a positive ion.
Some atoms already have full outer shells. These are: Helium, Neon, Argon, Krypton, Xenon
and Radon. These elements are said to belong to the Inert Gas family. Because they do not easily gain
or lose electrons, they do not react chemically with other elements. When other elements gain or lose
electrons they are attempting to mimic the electron configuration of a member of the inert gas family.
4. The Big Picture
When atoms of different elements react chemically they undergo a process of electron swapping.
The "most famous" example is the Sodium/Chlorine union. In this reaction, Na (sodium) loses an
electron to have its outer shell full and Cl (Chlorine ) gains an electron in order to have its outer shell
full. When Na loses its electron it becomes a +1 ion and when chlorine gains its electron it becomes a -1
ion. Since Na is positive and Cl is negative they attract one another and react chemically.
Figure 3: Electron Configuration of Sodium
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Science 9 – Chemistry Unit
Figure 4: Electron Configuration of Chlorine
Figure 5: The Bonding of Sodium and Chlorine
There are many ways to represent the electron configuration of elements and in the next two
pages three such ways are shown. The first diagram is intended to show how many electron positions
are available in each shell and that each shell is made up of even small subdivisions call subshells. The
next representation is the step model which is intended again to show the numbers of electrons in each
shell and the relative amounts of energy necessary for the electrons to exist in those shells. The higher
the shell is on the steps, the more energy is necessary to keep the electrons in that shell. When
occupying space around a nucleus, electrons will always fill the shells closest to the nucleus first and
then move outward until all of the electrons are used up. The final diagram is, of course, a part of the
Periodic Table of elements. It should be familiar to you since you developed this same portion in the
original activity in this chemistry section.
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Science 9 – Chemistry Unit
The Flame Test: Evidence for Electron Shells?
An electric current passing through a light bulb heats the tungsten filament. The heat causes the
filament to glow and it appears white hot. When an electric current is passed through a glass tube
containing neon, a red glow is produced. A wide variety of coloured neon lights is produced by adding
small amounts of other elements to the neon and by tinting the glass tube. Is the colour produced a
characteristic property of the gas? Do other elements produce a characteristic colour? Does the colour
of the light change when the element combines with other elements?
In this demonstration we will heat elements and compounds in a Bunsen Flame until they glow
or give off some light. The light produced colours the Bunsen flame. This procedure is called a flame
test. In the table provided, record the results of the experiment beside the name of the element or
compound used.
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Science 9 – Chemistry Unit
Questions:
1.
What evidence suggests that the flame colours are produced by the first or metallic element of a
compound?
2.
What is a "positive" flame test for each of the following: copper, calcium, potassium, strontium,
sodium, and barium?
3.
What is the definition of "characteristic property"? What evidence suggests that flame colour is a
characteristic property?
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Science 9 – Chemistry Unit
Ion Review:
This review should help to find what type of ion is formed by each of the first 20 elements in the
periodic table. Refer to the periodic table above for the necessary information. Remember that
Atomic Number is the same as the number of protons and the number of electrons in a neutral
atom. Also remember that the atomic weight minus the atomic number gives you the number of
neutrons. When filling in the charts start placing the atoms electrons in the bottom step and work
your way up until all of the available electrons are used up. Then to decide what type of ion is
formed, find out what would be the easiest way for the atom to have a full outer shell - by losing
some electrons or by gaining some electrons. The chart that you made should help you visualize
this need.
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Science 9 – Chemistry Unit
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Science 9 – Chemistry Unit
Directions: With the following pairs of elements, put the number of atoms of each necessary to create
a balanced compound.
#
1
2
3
4
5
6
7
8
9
10
Atoms
of Element 1
Be
Na
C
Li
Ca
P
Al
B
H
Si
Atoms
of Element 2
F
S
N
O
Si
N
O
F
C
S
Balancing Chemical Equations:
By now you should know what elements and compounds are; you should know what the
difference is between chemical symbols and chemical formulas. Molecular weight is the combined
weight of all of the atoms in a molecule of a compound. The next step to be taken is the balancing of
chemical equations. This is a skill that may at first seem very imposing but when one realizes that all
that is necessary is an understanding of the law of Conservation of Mass and lowest common
denominators, it all becomes relatively straight-forward.
Conservation of mass states that "in a chemical reaction, the mass of the reactants before the
reaction is equal to the mass of the products after the reaction". This comes from the fact that during a
chemical reaction new matter is not created and matter is not destroyed - atoms simply rearrange
themselves and attach to other atoms. The mathematical concept of lowest common denominators
comes into play because numbers of atoms of each element must be balanced on each side of a chemical
equation.
A simple example of a balanced equation is given below along with an explanation.
____ H + ____ O2 ----> ____ H2O
In this example, hydrogen (monatomic - exists as a one atom element) reacts with oxygen
(diatomic - exists as a two atom molecule) to give us water. On the left side there is one atom of
hydrogen and there are two atoms of oxygen. On the right side there are two atoms of hydrogen
and one atom of oxygen. Immediately an imbalance should be seen which violates the law of
conservation of mass. One can count the atoms of each element and make a table to keep track
of numbers. This table is filled with preliminary numbers of the equation the way you find it
originally. Later the values will be changed as you get closer to the balanced equation.
Before
Reaction
1 H
2 O
||
||
||
||
||
||
||
After
Reaction
2 H
1 O
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Science 9 – Chemistry Unit
If this equation was balanced the numbers for each element would be the same on both sides of
the table. Since they aren't, we must chose one of the elements to start with. We can start with
oxygen here (the reason for this choice will be given later). The question we must ask ourselves
is, "what is the lowest common denominator between the left side and the right side"? This is a
rather trivial example because the lowest common denominator is obvious - 2. The right side
must therefore be multiplied by two to achieve this common denominator.
Before
||
After
Reaction
||
Reaction
||
1 H
||
2 H
||
2 O
|| 2 x 1 = 2 O
||
In the chemical equation, the only way that we can accomplish this is to multiply the complete
water molecule by 2. We cannot just multiply the oxygen by 2 because this destroys the unique
structure of water - H2O. We can, however, say that there are two molecules of water. But when
we do this we must also adjust our table to reflect this multiplication.
____ H + ____ O2 ----> 2 H2O
Before
Reaction
||
After
||
Reaction
||
1 H
|| 2 x 2 = 4 H
||
2 O
|| 2 x 1 = 2 O
||
Now we must balance hydrogen and this can only be accomplished by multiplying the left side
by 4.
Before
||
After
Reaction
||
Reaction
||
1 x 4 = 4 H || 2 x 2 = 4 H
||
2 O
|| 2 x 1 = 2 O
||
The equation is now balanced if we put the numbers from the able into the equation.
4 H + 1 O2 ----> 2 H2O
As mentioned earlier the reason for the choice of oxygen as a starting point would be given. The oxygen
was solved first because on the right side it is in the more simpler form - there is only one atom
in the molecule. Hydrogen, on the other hand, is slightly more complicated since there are two
atoms of it in the molecule. As a rule, then, do the simpler elements first and then try to work
your way to the more difficult elements.
You will be given plenty of questions in the next exercise to practice this procedure.
Questions:
1.
The formula for table sugar is C12H22O11.
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Science 9 – Chemistry Unit
2.
3.
a.
How many atoms of hydrogen are found in the sugar molecule?
b.
What other atoms are present and how many of each?
c.
Translate the English phrase "three sugar molecules" into chemical symbols.
d.
What is the molecular weight of a molecule of table sugar?
The formula for the insecticide DDT is C14H9Cl5.
a.
What atoms combine to make DDT, and how many of each are present?
b.
How would a chemist symbolize "four DDT molecules"?
c.
What is the molecular weight of a molecule of DDT?
Balance the chemical equations that follow. Remember, you cannot change the chemical
formula of a molecule, you can only write numbers in front of the chemical formula.
a.
A smoldering fire:
coal (carbon) +
oxygen ------> carbon monoxide
C
+
O
------>
CO
b.
Scratching an aluminum can will reveal a shiny surface. This surface dulls quickly
according to the reaction:
aluminum
+
oxygen ------> aluminum oxide
Al
+
O
------>
Al2O3
c.
Burning Magnesium:
Mg
+
d.
e.
f.
g.
O2
------>
gas barbecue flame:
C3H8 +
O2
a soft drink fizzing:
H2CO3 ------>
H2O
+
photosynthesis:
CO2 +
H2O
------>
Acid rain:
SO3 +
H2O ------>
------>
MgO
CO2 +
H2O
CO2
C6H12O6 +
O2
H2SO4
Bibliography
Aikenhead, Glen S., Logical Reasoning in Science & Technology, Saskatoon:
University of Saskatchewan, 1988.
Andrews, William A, et al, Physical Science - An Introductory Course, Scarborough:
Prentice-Hall of Canada, Ltd., 1978.
Interaction Science Curriculum Committee, Interaction of Matter and Energy (second
edition), Chicago: Rand McNally & Company,1973.
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