Chemistry 20
Name: _____________
Unit II: Atoms and Elements
4.3 How Atoms Differ
I. Skim pages 98 - 104 of the textbook. After reading the headlines and looking
at the pictures predict 3 things that you think that you will be reading about in
this section.
1. _______________________________________________________
2. _______________________________________________________
3. _______________________________________________________
II. The learning objectives for this section are:
1. Define and give an example of: atomic number, isotope, mass number,
atomic mass unit (amu), and atomic mass.
2. Explain the role of atomic number in determining the identity of an atom.
3. Explain why atomic mass are not whole numbers.
4. Calculate the number of electrons, protons, and neutrons in an atom given
its mass number and atomic number.
5. Calculate atomic mass values when given the percentage of each isotope of
an element.
III. The following questions will help to cover these objectives as you read
through the section.
1.
What identifies an atom as belonging to a particular element?
2.
What can be determined by knowing an element’s atomic number?
3.
Read over the example problem on page 99 and work through practice
problems 11 – 13 on the same page (use the back of the book for to check
your answers. Complete the following:
a) How many protons and electrons are contained in an atom of element 44?
b) For each of the following chemical symbols, determine the element name
and the number of protons and electrons an atom contains.
Chemical symbol
V
Ir
Mn
S
4.
Element name
# of protons
# of electrons
Why was Dalton’s Atomic Theory point about all atoms of a particular
element are identical slightly incorrect?
5.
How do isotopes differ from each other in a particular element?
6.
Explain why isotopes of a particular element still have the same chemical
behaviours?
7.
How are the number of neutrons, the mass number, and the atomic number
of a particular element all related to one another?
8.
Draw and explain the notation you see in Figure 4-15 on page 100.
9.
Read over the example problem on page 101 and work through practice
problem 14 on the same page (use the back of the book for to check your
answers. Complete the following:
a) A carbon atom has a mass number of 12 and an atomic number of 6. How
many neutrons does it have?
b) An isotope of mercury has 80 protons and 120 neutrons. What is the
mass number of this isotope?
c) An isotope of xenon has an atomic number of 54 and contains 77 neutrons.
What is the xenon isotope’s mass number?
d) Complete the following table.
The number after the element name refers to the atomic mass.
Isotope
132
55Cs
59
27Co
163
69Tm
70
30Zn
gallium-64
fluorine-23
titanium-48
helium-8
10.
# of electrons
# of protons
# of neutrons
Why are atomic masses not whole numbers on the periodic table?
11.
Read over the example problem on page 103-104 and work through practice
problems 15-17 on the same page (use the back of the book for to check
your answers. Complete the following:
a) In your own words list the steps in the process of calculating average
atomic mass given data about the isotopes of an element.
b) Chlorine, which has an atomic mass of 35.453 amu, has two naturally
isotopes, Cl-35 and Cl-37. Which isotope occurs in greater abundance?
Explain.
c) Silver has two isotopes,
109
47Ag
silver?
107
47Ag
has a mass of 106.905 amu (52.00%), and
has a mass of 108.905 amu (48.00%). What is the atomic mass of
d) Data for chromium’s four naturally occurring isotopes is provided in the
table below. Calculate chromium’s atomic mass.
Isotope
Cr-50
Cr-52
Cr-53
Cr-54
Percent abundance
4.35%
83.79%
9.50%
2.36%
Mass (amu)
49.946
51.941
52.941
53.939