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3.5 Isotopes I
On Your Desk:
 This packet
 Syllabus
 Writing utensil
Expectations:
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Students will work quietly and respectfully.
Students will raise their hand before speaking
Students will not leave their seat.
Teacher will respect and encourage all questions
Teacher will enforce all rules and expectations
Do Now:
Directions: Get out your homework from yesterday, and set it out on your desk. Ms. Carney will check to
ensure that your homework is completed as you silently work on the do now below.
1. The atomic number of an atom is equal to the number of _______________________.
2. Write a general definition for isotope.
3. Thinking back to the POGIL activity yesterday, can two atoms with the same mass number ever be
isotopes? Why or why not?
4. A neutral atom has 14 protons and 18 neutrons. Write the correct symbol for this atom.
5. Which of the following pairs show two atoms with the same number of neutrons?
38
a. 37
17𝐶𝑙 and 18𝐴𝑟
32
b. 32
15𝑃 and 16𝑆
59
c. 27
𝐶𝑜 and 61
27𝐶𝑜
6. There are three stable isotopes of Argon: Argon-36, Argon-38, and Argon-40. What would the atoms of
these isotopes have in common? What would be different about their atoms?
Isotopes: (I Do)
Definition:
The simplest example of an atom with different isotopes is hydrogen. The three isotopes of hydrogen are shown
below:
 The increasing number of__________________ in the nucleus of the hydrogen atom adds _________________ to the
atom and thus each isotope of a given element has a different mass.
Isotope Representation:
23
11Na
-
Hydrogen:
-
Deuterium:
-
Tritium:
Understanding Isotopes (We Do)
Here are three isotopes of an element:
a. The element is: __________________
12
6 C
13
6 C
14
6 C
b. The number 6 refers to the _________________________
c. The numbers 12, 13, and 14 refer to the ________________________
d. How many protons and neutrons are in the first isotope? _________________
e. How many protons and neutrons are in the second isotope? _________________
f.
How many protons and neutrons are in the third isotope? _________________
Directions: Using the notation above, write the following isotope’s symbols:

Silver: 61 neutrons; 47 protons

Lead: 125 neutrons; 82 protons

Potassium: Mass number 39

Challenge! Element: Mass number 12; atomic number 6 (Hint: Find the element on the periodic table!)
Complete the following chart:
Isotope name
Uranium-235
Uranium-238
Boron-10
Boron-11
atomic #
mass #
# of protons
# of neutrons
# of electrons
Isotope Symbol
Isotopes Practice (You Do)
How can you tell isotopes apart?
For each of the following isotopes, write the number of protons, neutrons, and electrons.
Chromium-58
Chromium-63
# of protons
# of protons
# of neutrons
# of neutrons
# of electrons
# of electrons
Sodium-12
Sodium-20
# of protons
# of protons
# of neutrons
# of neutrons
# of electrons
# of electrons
Nitrogen-15
Nitrogen-20
Carbon-12
Carbon-16
Fill in the isotope names and any missing information, including isotope numbers from the chart. Use your
periodic table and the information provided.
# of protons
# of neutrons
# of protons
25
17
15
# of electrons
32
# of neutrons
30
# of electrons
Iron# of protons
# of neutrons
# of electrons
32
Iron-
# of protons
48
51
46
# of neutrons
# of electrons
27
30
Understanding Isotopes Worksheet (HW)
Name:
Use the information from the periodic table of the elements to complete the questions
1. What are isotopes?
____________________________________________________________________________________
____________________________________________________________________________________
2. How many protons do carbon atoms have? ______
3. How many neutrons are there in the most common form of the carbon atom?
______
4. How many neutrons are there in a C-14 atom? ______
5. How many protons do oxygen atoms have? ______
6. How many neutrons are there in the most abundant isotope of oxygen atoms (O-16)? ______
7. How many neutrons does 18O have? ______
8. Describe the atomic structure (Number of protons, electrons and neutrons) found in 87Sr:
Protons:
______
Neutrons
______
Electrons
______
9. Complete the table below by deciding if the elements A and B described in each row are isotopes of
each other or if they are different elements:
Protons
Electrons
Neutrons
Element a) 92
Element b) 92
Element a) 92
Element b) 92
Element a) 146
Element b) 143
Element a) 8
Element b) 6
Element a) 8
Element b) 6
Element a) 8
Element b) 8
Element a) 1
Element b) 1
Element c) 1
Element a) 1
Element b) 1
Element c) 1
Element a) 0
Element b) 1
Element c) 2
Isotopes or Different Elements?