Name:____________________________
CHEM 121_ LWIT
Worksheet 2- Isotopes
1. What is the mass in atomic mass units (amu) of a nitrogen atom weighing 2.33 x 10-23 g.
(remember: 1 amu = 1.660539 x 10-24 g)
2. How many atoms are in each of the following:
a. 1.0g Hydrogen atom; each hydrogen atom is 1.0 amu
b. 12.0g of carbon atoms; each of mass 12.0 amu
c. 23.0 g of sodium atoms; each of mass 23.0 amu
3. What pattern do you see in your answer to question 2?
4. a) What is an isotope?
____________________________________________________________________________
________________________________________________________________________________
b) What does the number next to isotopes signify? _______________________________________
________________________________________________________________________________
c). How can you tell isotopes of the same element apart? __________________________________
________________________________________________________________________________
5. Here are three isotopes of an element:
12C
6
13C
6
14C
6
a. The element is: __________________
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? _________________
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6. Complete the following table
7. For each of the following isotopes, write the number of protons, neutrons, and electrons.
Assume all atoms are neutral.
Selenium-50
Chromium-58 Chromium-63
Selenium-55
# of protons
# of protons
# of neutrons
# of neutrons
# of electrons
# of electrons
DIRECTIONS: For the following problems, show your work! Be thorough.
8. Naturally occurring europium (Eu) consists of two isotopes was a mass of 151 and 153. Europium151 has an abundance of 48.03% and Europium-153 has an abundance of 51.97%. What is the atomic
mass of europium?
9. What is the atomic mass of hafnium if, out of every 100 atoms, 5 have a mass of 176, 19 have a mass of
177, 27 have a mass of 178, 14 have a mass of 179, and 35 have a mass of 180.0?
2
10. Boron exists in two isotopes, boron-10 and boron-11. Based on the atomic mass, which isotope
should be more abundant?
11. PART III. Fill in the isotope names and any missing information on the chart. Use your
periodic table and the information provided. Assume all atoms are neutral.
# of protons
# of protons
25
32
# of neutrons
# of neutrons
17
15
# of electrons
# of electrons
# of protons
# of protons
# of neutrons
# of neutrons
48
51
# of electrons
30
32
113
111
# of electrons
46
Iron-
55
Iodine-
Iron-
# of protons
# of protons
# of neutrons
# of neutrons
27
32
30
# of electrons
# of electrons
3
Iodine-
35
Germanium-
Germanium-
-10
# of protons
-12
# of protons
6
# of neutrons
33
# of neutrons
36
# of electrons
# of electrons
6
-22
-25
-54
# of protons
# of protons
24
# of neutrons
# of neutrons
# of electrons
# of electrons
11
4
-56