Science 10 – Chemical Reactions Unit
What is chemistry?
Chemistry is the study of matter and its properties and it changes or its transformations. As you know,
matter is anything that has mass and is found around you. So, chemistry is the study of all changes that
go on around you. Can you think of any examples that would outline how you used chemistry this
morning?
What chemicals do you use in your home? Are any dangerous? Do you use chemicals outside? Are
they dangerous?
All matter has physical properties and chemical properties. A physical property is a characteristic of
something that you can see, hear, taste, smell or even feel like the colour, odour, or even the state of
matter (solid, liquid or gas). A chemical property is a characteristic that occurs when a substance
changes to a new substance, often irreversible. These properties are often used to identify if a
substance has undergone a physical or a chemical change. Please complete the interactive practise
found at http://www.teacherbridge.org/public/bhs/teachers/Dana/chemphys.html.
Topic 1 – Classifying Substances
Please consider the following figure (can also refer to page 172 of the text for a similar figure):
A few definitions from the figure:
Mixture – Contains two or more substances
Pure Substance – is one in which all the particles that make up the substance are the same
Elements – Can not be broken down into simpler substances
Compounds – contain two or more different elements in a fixed proportion
So, we basically divide matter into two main categories, either mixtures or pure substances.
Topic 2 – The Atom
Basically, an atom is made up of protons, neutrons and electrons. In the centre of the atom is a
nucleus, which is membrane bound, containing both the protons and neutrons. The electrons
move around the nucleus in large orbitals which allow the electrons to be in constant motion.
These orbitals are often called shells and it must be noted that the closer an electron is to the
nucleus, the lower energy that it has. A basic representation of an atom:
The whole atom is held together by two different types of forces. The first is the electric charge
between the proton (+) and the electron (-). Electrons are always attracted to the protons
meaning that they will continue to follow a somewhat circular pattern moving around the
nucleus. The second force holding the atom together is the force that is required to hold the
membrane of the nucleus in place so that the protons and neutrons stay put. The problem with
holding the nucleus together is that the protons will all repel each other because they carry the
same electrical charge. As a result, the force must be stronger than the electrical charge to
make them stay beside each other. Scientists have named this force the strong force as it is
stronger than the electrical and holds all together. To consider how strong the force is we can
look at the energy found in a nuclear reaction (bomb) which is created by splitting apart the
nucleuses of atoms.
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. 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. The electrons in a many
electron atom are arranged in energy levels about the
nucleus. The electrons in their lowest energy state (termed
ground state) occupy these energy levels from lowest (closest
to nucleus) to highest energy. Only certain numbers of
electrons can be placed in each energy level.
Characteristics of an Atom
1. The number of protons in the nucleus of an atom is termed it's atomic number.
This number is distinctive (characteristics) for the atoms of each element.
Atomic Number = # of protons
2. The number of neutrons in the nucleus of an atom is not
distinctive and may vary. This creates varieties of atoms we
call isotopes. In the example to the right, three isotopes of
hydrogen are illustrated. Each isotope has one proton (red),
but each has a different number of neutrons (blue).
Isotopes are atoms of the same element with different numbers of neutrons.
3. Another characteristic of an atom of an element is it's atomic mass (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.
4. 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.
For Example: If Magnesium loses two electrons it would have 12 + charged protons and
only 10 - charged electrons and would become a +2 ion. If Chlorine gains one electron it
would have 35 protons (+) and 36 electrons (-) and become a - 1 ion. The charge on the
ion indicates the number of electrons gained or lost.
We use the Bohr-Rutherford model of an atom to determine the general appearance and the properties
of an atom. In this model, there is a central nucleus that holds the protons and neutrons, while the
electrons are found in levels on the outside of the nucleus.
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To draw BohrRutherford
diagram for
Boron we place
the first 2
electrons in first
shell.
The first shell
can only hold a
maximum of 2
electrons so we
start filling the
second shell
The Boron
atom has 5
electrons
therefore we
have another 3
electrons to
place
We place these
electrons in the
Second shell
and we space
them apart from
one another
We can use Bohr Diagrams to help represent an atom. To draw a Bohr Diagram, the first electron shell
has only 2 electrons, the second has 8 and for any element with less than 20 electrons, the third orbit
can also only have 8.
Let us draw Bohr Diagrams for: Lithium (3 electrons), Flourine (9 electrons), Sulfur (16 electrons) and
Calcium (20 electrons).
We can also draw Lewis Dot Structures of each of the elements and will learn this skill in topic 3.
Topic 3 – Elements and the Periodic Table
The periodic table is a structured arrangement of elements used to help us explain and predict the
chemical and physical properties of elements and their families. Some keys to the periodic table:
1. Metals on the left, non metals on the right. Locate the staircase line and follow it down. It
separates the metals and the non metals. (Exception – hydrogen) How metals and non metals
different?
Please refer to page 184, 185, 186 of the text with special attention to Table 1.
2. The atomic number is equal to the number of protons, which equals the number of electrons
unless there is a charge (ion).
3. The charge can often be determined by the family
What are families? To help us determine this, we are going to complete the Periodic Table Basics
activity handout. Do not cut out the cards and make squares, but rather create a table in your book
similar to Table 3.
To make the Lewis Dot structures, we focus on the number of valence electrons around the element.
This is the number of electrons in the outer level. For elements 1 and 2, there can only be a maximum
of 2, for elements 3-10 a maximum of 8 and for elements 11-18 a maximum of 8.
Now that we have completed this first activity, we need to set up our periodic table. Please compete
the following:
1. Staircase line
2. Families (use different colours)
3. Charges
Please complete the Bohr Diagrams and Lewis Dot Diagrams handout for hand in.
Please complete the Structure of an atom worksheet.
Topic 4 – How Elements form Compounds
Please read Pg. 188-89 and complete #1-3 and answer the question: Please explain how ionic and
molecular compounds are different?
Topic 5 – Ionic Compouds
Please read Pg. 192-195 and complete Pg. 195 # 1-8
Topic 6 – Polyatomic Compounds
Please read Pg. 196-198 and complete Pg. 198 #1-4
Topic 7 Molecular Compounds
Please read Pg 201-204 and complete Pg. 204 #1-6
Complete the following handouts: Types of Chemical Bonds, Ionic Bonding (both sides), Molecules and
Compounds
Topic 8 Synthetic vs. Natural
This is for your own knowledge. Please read Page 208-212.
For hand in please complete Page 214-15 #1, 3, 4-11
Topic 9 – Word Equations
The major thing to understand is that reactants are on the left and products are on the right. Try the
activity on Page 219 followed by Pg. 219 #1-3. Please complete the handout Word Equations
Worksheet.
Topic 10 – Conservation of Mass
Please understand that in all chemical reactions the amount of mass found in the reactants will also be
found in the products, meaning that all mass has been kept constant. This is known as the Law of
Conservation of Mass. Please read Page 222-223 and complete questions #1-5.
Topic 11 – Balancing Chemical Equations
Begin by completing the handout Counting Atoms Worksheet. We will then read Page 226-229 and
complete #1-4 on page 229.
Please complete Chemical Equations and Stoichiometry Balancing Equations Sheet.
Topic 12 – Types of Chemical Reactions
There are four major categories:
1. Synthesis – Putting together (Page 234)
2. Decomposition – Pulling apart (Page 235)
3. Single Displacement – Involve an element and a compound as reactants (P. 240)
4. Double Displacement – involve two compounds as reactants (P. 241)
Please complete the classification of chemical reactions worksheet.
Topic 13 – Factors that affect the Rate of Reaction
We will begin by completing Investigation 7.1 found on page 256-57.
First, we must consider that molecules collide all the time, but do not always result in a chemical
reaction. This is known as the collision model. For a chemical reaction to occur the collision must have
enough energy to react and have the proper geometry to each other. So, to increase the rate of a
reaction we must either increase the number of collisions, or the number of collisions that are successful
by the addition of energy.
1.
Temperature: Increasing the temperature causes molecules to move quicker and have
increased energy. More movement causes more collisions and increased energy means more
collisions will result in chemical reactions.
2. Concentration: Increasing the concentration means that there will be more collisions, meaning
an increase in the reaction rate.
3. Surface Area: Increasing the surface area will increase a reaction rate because there more
collisions resulting from the increased area of reactants to collide.
4. Catalysts: Speeds up the rate of the reaction without actually entering in the reaction usually by
lowering the amount of energy required
Read pages 278, 279, and 280 and explain how we preserve foods with the use of the four factors above
and the collision theory.
Topic 14 – Properties of Acids and Bases
Using pages 293 and 294 create a T-chart showing the properties of both acids and bases side by side.
When looking at chemical formulas, acids usually begin with a hydrogen and tend to donate a hydrogen
atom. Bases tend to accept a hydrogen atom and usually have a hydroxide ion (OH-).
Please complete Page 295 #3-5.
Topic 15 – The pH Scale
Please read Page 296-299 and complete #2-10
Topic 16 – Air Pollution and Acid Precipitation
Please read Page 308-312 and complete #7.
Topic 17 – Neutralization Reactions
The products of these reactions involving an acid and a base are often a salt and water. Refer to page
317-319 and complete 3 and 4.
Exam!