http://www.ck12.org Chapter 24. Nuclear Chemistry
24.1 Nuclear Radiation
Lesson Objectives
- Describe the characteristics of radioactive emissions.
- Complete equations involving radioactive decay when given pertinent information.
- Describe how to measure radioactivity.
Lesson Vocabulary
- radioactivity: The spontaneous emission of matter and/or energy from the unstable nucleus of an atom.
- alpha particle: The nucleus of a helium-4 atom
- beta particle: An electron.
- gamma radiation: Very high energy electromagnetic radiation.
- Geiger counter: A device that measures the frequency of radioactive events; composed of a tube filled with
an inert gas that is able to conduct electricity when exposed to charged radiation.
Check Your Understanding
Recalling Prior Knowledge
- How are mass number and atomic number related to the amounts of different subatomic particles in a particular
atom? - What is different about multiple isotopes of a single element?
A Review of Isotopes
John Dalton first proposed his atomic theory in an 1804 lecture to the Royal Institution, a prestigious British
scientific society. In this talk, he put forth the idea that all atoms of an element were identical and that atoms
were indestructible. In a little over 100 years, both of these ideas were shown to be incorrect. Studies on atomic
weights led Frederick Soddy (1877-1956) to the conclusion in 1913 that atoms of a single element can have more
than one possible atomic weight. He won the Nobel Prize in Chemistry for this work in 1921.
At least by our current understanding, a given atom can be defined by its atomic number and its mass number. The
atomic number is the number of protons in the nucleus. All atoms with a given atomic number are the same element,
because the chemical properties of an atom are primarily determined by the number of positive charges in its nucleus
(and therefore the number of negatively charged electrons needed to make it neutral). The mass number of an atom is
equal to the number of protons plus the number of neutrons. Since these particles both have a mass of approximately