Chemistry 2.05 – 2.08 SG S1
1. Isotopes:
2. isotopes of an element have different numbers of _________________, they also have different
________________ numbers.
3. Most __________________ occur naturally as mixtures of isotopes.
4. The mass numbers on the periodic table are the ____________________ average of the most
abundant isotopes’ mass numbers.
5. Atomic Mass
a.
b.
c.
d.
6. To calculate the _________________ __________________ of an element, ______________ the
mass of each isotope by its natural abundance, expressed as a decimal, and then add the
products.
7. Calculating Atomic Mass
a.
b.
c.
d.
8. Given the average atomic mass of an element on the periodic table and the percent natural
abundance of each isotope, calculate the identity of the unknown isotope?(Atomic mass of
chromium is 51.996 amu)
Isotope
% abundance
Fraction of
abundance
Mass
9. Chlorine has two naturally occurring isotopes. The mass of chlorine-35 is 34.696 amu and the
mass of chlorine-37 is 36.966 amu. Using the average mass from the periodic table (average
atomic mass of chlorine is 35.453), find the abundance of each isotope. (Remember that the
sum of the two frctional abundances must be 1)
Isotope
% of
abundance
Fraction of
abundance
Mass
10. The mass of a Cu-63 atom is 62.94 amu, and that of a Cu-65 atom is 64.93 amu. The percent
abundance of Cu-63 is 69.17% and the percent abundance of Cu-65 is 30.83%. What is the
average atomic mass?
Isotope
% abundance
Fraction of
abundance
Mass
11. Calculate the average atomic mass of chromium. It is made up of isotopes with the following
percent compositions and atomic masses: 83.79% with a mass of 51.94 amu; 9.50% with a mass
of 52.94 amu; 4.35% with a mass of 49.95 amu; 2.36 % with a mass of 53.94 amu.
Isotope
% abundance
Fraction of
abundance
Mass
12. Calculate the average atomic mass of iron if its abundance in nature is 15% iron-55 and 85%
iron-56.
Isotope
% abundance
Fraction of
abundance
Mass