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Module 2 – Chemistry in Action
Introduction to Chemistry in Action
We are all a collection of chemicals. All plants and animals are collections of
chemicals. The Earth is a collection of chemicals. To understand how and why
changes in substances happen we must study chemistry. Chemistry is the
study of the composition of substances and the changes that the substances
undergo.
Chemistry allows us to understand what things around us are made of and how
to use them. Understanding chemistry also allows us to produce new materials.
As you study chemistry, you must also study how chemistry related issues
affect your life and society as a whole.
You will have to make personal choices in your life. Should I use this
chemical? What are the harmful effects it has on people and the environment?
Are there other chemicals that are just as effective but safer to use?
In society, you will influence public decisions in your community, your
province and your country. Should some chemicals such as pesticides be
banned from use on lawns? Should the government institute stricter regulations
on industry to curb the release of chemicals into the environment? What
chemicals are released into the environment? What are their effects? What new
chemicals should be allowed to be produced?
In order to function, both at an individual level and as a citizen of society, you
must be chemistry literate. You must be able to understand the chemistry
behind the issues in order to make an informed decision.
Chemistry in Action Concept Map
The following is a chemistry concept map which outlines many of the concepts
which you may be studying in the module. A concept map is provided as an
outline to illustrate how ideas fit together, that is, the big picture into which all
the details will fit.
Lesson 1: Review of Atomic Model
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Introduction
It has taken scientists a long time to understand the basic structure of an atom. Many
scientists have carefully worked together to make known the structure of atoms.
You have studied this development in Science 10F. We will use a short review to refresh
your memory about the structure of atoms that is relevant to your study this year.
Outcomes
After completing this lesson, you will be able to
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use the modern atomic theory to describe the meaning of the terms atomic number,
mass number, and atomic mass
predict the number of protons, electrons, and neutrons knowing the atomic number
and the mass number of an atom
state the charge, location, and mass of the subatomic particles
calculate the atomic mass of an element knowing the mass number and atomic
number of the atom
Atomic Theory - Review
Dalton's theory for the structure of the atom stands fundamentally correct today. His understanding that atoms
cannot be broken down, however, has been proven incorrect. Atoms can be broken down into subatomic
particles. A subatomic particle is a part of an atom much the same as a wheel is part of a car. The three main
subatomic particles are protons, neutrons, and electrons. The scientists Thompson, Rutherford, Bohr,
Moseley, and Chadwick were largely responsible for developing an understanding of subatomic particles.
Today, scientists know subatomic particles in turn can be broken down into still smaller particles.
The Bohr model of the atom suggested that electrons travel in a circular orbit or energy level in a well-defined
path. Scientists have done experiments to show that this is not the path electrons actually travel. Electron
location and movement is more complicated than Bohr thought; however, the planetary model of the atom is
used because it is easier to understand and is adequate for a beginning course in chemistry.
The modern atomic theory states that an atom consists of:

Protons located in the nucleus of the atom. Protons have a positive charge and a mass of one atomic
mass unit (u). An atomic mass unit is defined as 1/12th the mass of a carbon atom that has six protons
and six neutrons. This means that 1u is equal to the mass of a proton.

Neutrons, also located in the nucleus of the atom. Neutrons have no electrical charge and have a
mass of approximately 1u.
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Electrons, located around the nucleus in less well-defined orbits than first thought. Electrons have a
single negative electrical charge but their mass is considered zero since it is so small(approximately
1/2000 the mass of a proton).
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Altogether, an atom consists of a dense nucleus surrounded by electrons moving in space.
Key Words – Define each of the following terms using the internet and provide an example
subatomic particle
energy levels
atomic mass
atomic mass unit (u)
atomic number
Nucleus
A nucleus is made of protons and neutrons.
Protons and neutrons both have a mass of 1u.
Protons have a positive charge (+1), neutrons have no charge.
The total mass of the atom is equal to the sum of the masses of the protons and neutrons in
the nucleus
If an atom were the size of a football stadium, the nucleus would be the size of a football.
The atomic number of an atom is equal to the number of protons in the nucleus.
The atomic mass number is equal to the sum of the number of protons and neutrons. The
atomic mass is expressed in atomic mass units (u).
Electrons
Electrons move around the nucleus in specific paths called energy levels.
Energy levels exist whether there is an electron in them or not.
Electrons occupy certain energy levels depending on the atom. For example, hydrogen has a
single electron in the first energy level. Sodium has two electrons in the first energy level,
eight electrons in the second energy level and one electron in the third energy level.
An atom can have a maximum of two electrons occupying the first energy level, eight in the
second energy level and eight in the third energy level. We will not study the structure of
atoms with more than three levels of energy levels. Each energy level must be filled before
electrons occupy the next one.
Electrons are so light they are considered to have zero mass.
Electrons have a negative electric charge (-1).
Exercise 1
Copy the following table into your notes and fill it in.
Charge
Location
Mass
Discovered by
Protons
Electrons
Neutrons
How do atoms of different elements differ from each other?
All atoms are made of protons, neutrons, and electrons (i.e., a proton in a carbon atom is the
same as a proton in an oxygen atom). The same is true for electrons and neutrons. What
determines the difference between atoms of different elements if they are all made of the
same subatomic materials? The answer is that atoms of different elements have different
numbers of protons in the nucleus and electrons around the nucleus.
Atomic Number
Henry Moseley originally developed the concept of the atomic number. An atom's atomic
number is equal to the number of protons in that atom's nucleus. The atomic number is
special because it can be used to identify any known element. It is easy to identify copper
because it has an atomic number of 29. Carbon has an atomic number of six, oxygen has an
atomic number of eight, and so on. The atomic number of every element is recorded in the
Periodic Table of Elements.
Mass Number
All atoms have a mass number. The mass number is equal to the number of protons plus the
number of neutrons (e.g., carbon has six protons and six neutrons).
The mass number for carbon would be 6 (protons) + 6 (neutrons) = 12.
Mass number = atomic number (number of protons) + number of neutrons
The atomic mass of an atom is expressed in atomic mass units (u). This means the atomic
mass of carbon is expressed as 12 u.
Mass number can be expressed as a number with no unit (12 for carbon) and atomic mass is
expressed using the same number with a unit (12 u for carbon) called atomic mass units.
You can solve for atomic number and number of neutrons by modifying the formula shown
above.
Atomic number = mass number - number neutrons
Number of neutrons = mass number - atomic number
Exercise 2
Use your understanding of mass number to calculate the values for the blank spaces in the
table below. Place the proper symbol for the elements in the brackets.
Refer to the periodic table of elements. Place the atomic symbol in the brackets following
the names in the table below. Fill in the blanks with the values for the atomic number and
number of protons.
Iron
(_____)
Atomic Number
Number of
Protons
Krypton
(_____)
Uranium
(_____)
Sodium
(_____)
Lithium
(_____)
Chlorine
(_____)
Number of
Protons
3
17
Number of
Neutrons
4
Copper
(_____)
47
34
Mass number
35
Silver
(_____)
61
63
Determining the number of subatomic particles
Number of protons
The number of protons is equal to the atomic number.
Number of electrons
All atoms are electrically neutral; that is, they have equal numbers of protons and electrons.
In any atom the number of electrons is equal to the atomic number.
Number of neutrons
The mass number is always equal to the number of protons plus the number of neutrons.
The number of neutrons would then be equal to the mass number minus the atomic number.
Number neutrons = mass number - atomic number
Calculating the Number of Subatomic Particles
Number of Protons
Atomic number
Number of neutrons
Mass number - Atomic number
Number of electrons
Number of protons or Atomic number
For example, mercury has an atomic number of 80 and a mass number of 200. What is the
number of protons, neutrons and electrons in one atom of mercury?
Number of protons = Atomic number = 80 protons
Number of electrons = Number of protons = 80 electrons
Number of neutrons = Mass number – Atomic number = 200 - 80 = 120 neutrons
Summary
An atom is made of protons, neutrons and electrons. Electrons travel in defined orbits or
energy levels around the nucleus.
Atomic number is equal to the number of protons. Atomic number identifies the type of
atom. In a neutral atom the number of protons and electrons is the same.
Atomic mass is equal to the number of protons plus the number of neutrons
Exercise 3
Answer the questions in a word processing document or on a sheet of paper.
An atom of gold has an atomic number of 79 and an atomic mass of 197u.
a. How many protons are there in one atom of gold?
b. How many electrons are there in one atom of gold?
c. How many neutrons are there in one atom of gold?
d. How many protons are there in 10 atoms of gold?
e. What is the atomic mass of gold?
f. What is the mass number of gold?
2. What is the unit of atomic mass called and what is its symbol?
3. An atom of uranium has an atomic number of 92 and an atomic mass of 238u.
a. How many protons are there in one atom of uranium?
b. How many electrons are there in one atom of uranium?
c. How many neutrons are there in one atom of uranium?
d. How many protons are there in 10 atoms of uranium?
e. What is the atomic mass of uranium?
f. What is the mass number of uranium?
Assignment
Part A: Complete each statement by filling in the blank with the correct answer.
1. The ____________ number gives the identity of an atom.
2. The atom of any element is neutral because the number of ________________
equals the number of ____________________.
3. The mass number consists of the number of _______________ plus the number
of _____________________in an atom.
4. The subatomic particles found in the nucleus are the ________________ and
the _______________________.
5. The subatomic particle that carries a charge of +1 is the __________________
while the particle that carries a charge of -1 is the
_________________________.
6. The symbol for an atomic mass unit is _______________________.
Part B: Write the answer on the table provided after each question. You will need your periodic
table for this question.
An atom has an atomic number of 49 and a mass number of 115.
a) Which element is this? Give the name and
the symbol.
b) How many protons does one atom contain?
c) What is the atomic mass of this atom?
d) What is the number of electrons in this
atom?
e) What is the number of neutrons in this atom?