Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
39
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 4
13. The atomic mass of bromine given in the periodic table is
79.904 amu, which is very close to 80 amu. Use a reference
book to find the percent of Br-80 in naturally occurring
bromine. Explain the value of the atomic mass of bromine from
the data you find.
14. The element chlorine occurs in nature as a mixture of two isotopes. Chlorine-35 has an atomic mass of 34.969 amu and
makes up 75.77% of chlorine atoms. Chlorine-37 atoms make
up the remaining 24.23% of all chlorine. Use the average
atomic mass of chlorine from the periodic table to calculate the
atomic mass of Cl-37 atoms.
4.4 Unstable Nuclei and Radioactive Decay
Dalton thought that atoms were unchangeable. However, scientists in
the late nineteenth century began to notice that some elements spontaneously emitted energy and particles. These emissions became
known as radiation. Elements that give off radiation are said to be
radioactive. Soon, scientists discovered that radioactive elements
changed into other elements after emitting radiation. Thus, atoms
were not unchangeable as Dalton had thought.
Today, we know that some nuclei are unstable and gain stability
by emitting radiation. This process is called radioactive decay.
Types of radiation Three principal types of radiation are given off
during radioactive decay. One type is alpha radiation (␣-radiation),
which consists of alpha particles ejected from the nucleus. An alpha
particle is equivalent to a helium-4 nucleus, that is, a nucleus with two
protons and two neutrons. Alpha particles have a 2ϩ charge.
␣-particle: 4
2 He (contains 2p ϩ and 2n 0 )
The second common type of radiation is beta radiation, which
consists of high-energy electrons called beta particles (-particles).
-particle: Ϫ1
0  (high-energy e Ϫ )
It is important to realize that each of these beta particles is emitted
by the atom’s nucleus, thereby increasing its atomic number (and
charge) by 1ϩ.
▲
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
39
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 4
13. The atomic mass of bromine given in the periodic table is
79.904 amu, which is very close to 80 amu. Use a reference
book to find the percent of Br-80 in naturally occurring
bromine. Explain the value of the atomic mass of bromine from
the data you find.
14. The element chlorine occurs in nature as a mixture of two isotopes. Chlorine-35 has an atomic mass of 34.969 amu and
makes up 75.77% of chlorine atoms. Chlorine-37 atoms make
up the remaining 24.23% of all chlorine. Use the average
atomic mass of chlorine from the periodic table to calculate the
atomic mass of Cl-37 atoms.
4.4 Unstable Nuclei and Radioactive Decay
Dalton thought that atoms were unchangeable. However, scientists in
the late nineteenth century began to notice that some elements spontaneously emitted energy and particles. These emissions became
known as radiation. Elements that give off radiation are said to be
radioactive. Soon, scientists discovered that radioactive elements
changed into other elements after emitting radiation. Thus, atoms
were not unchangeable as Dalton had thought.
Today, we know that some nuclei are unstable and gain stability
by emitting radiation. This process is called radioactive decay.
Types of radiation Three principal types of radiation are given off
during radioactive decay. One type is alpha radiation (␣-radiation),
which consists of alpha particles ejected from the nucleus. An alpha
particle is equivalent to a helium-4 nucleus, that is, a nucleus with two
protons and two neutrons. Alpha particles have a 2ϩ charge.
␣-particle: 4
2 He (contains 2p ϩ and 2n 0 )
The second common type of radiation is beta radiation, which
consists of high-energy electrons called beta particles (-particles).
-particle: Ϫ1
0  (high-energy e Ϫ )
It is important to realize that each of these beta particles is emitted
by the atom’s nucleus, thereby increasing its atomic number (and
charge) by 1ϩ.
▲