Chemistry Reference
In-Depth Information
element on each side of a chemical equation, or else it violates the Law of
Conservation of Mass. The equation shown here does not represent a chemi-
cal reaction, because it does violate the Law of Conservation of Mass!
Way back in Chapter 1 I mentioned that Einstein combined the laws of
conservation of mass and energy into one law, called the Law of Conserva-
tion of Mass-Energy to account for the fact that in a nuclear reaction, a
small amount of mass is converted into energy. Perhaps the most interest-
ing aspect of nuclear reactions is the fact that elements actually transform
into other elements. Sometimes, when we hear stories of the ancient alche-
mists trying to turn lead into gold, we scoff at their “primitive” notations,
which seem to blur magic and science. What is interesting is that humans
now have the ability to do what the alchemists dreamed of doing: We can
change one element into another. In fact, it happens in nature all of the
time!
So, when you see an equation such as , where you
have different elements on each side of the equation, you should know
right away that you are looking at a nuclear equation. Notice that both the
mass number
40
K
40
Ca +
0
e
and the nuclear charge
19
K
20
Ca +
-1
e
of the
particles that appear in the equation are conserved, because this will be
the key to balancing this type of equation. In reality, you should realize
that nuclear reactions do involve mass-energy conversions, so you can't
expect the original Law of Conservation of Mass to apply to nuclear reac-
tions. Rather, it is the sum of the mass and the energy that is conserved in a
nuclear reaction. Such a small amount of matter is converted into energy
that you won't notice the missing mass in the actual nuclear equation.
Before we learn more about the types of nuclear reactions, you should
become familiar with the types of notation that are used for the particles
that are common to nuclear reactions shown in Figure 6-5a on page 205.
In addition to the symbols shown in Figure 6-5a, you should also be-
come familiar with the symbol
γ
, which represents another type of radia-
tion called gamma rays or gamma radiation. The symbol for gamma
radiation wasn't included in Figure 6-5a, simply because gamma rays are a
form of electromagnetic radiation and are usually not thought of as par-
ticles. (You may get to wait until you study physics until you open this par-
ticular can of worms.)
Nuclear processes are often categorized as natural radioactivity or arti-
ficial radioactivity. As you might imagine, the term natural radioactivity is
applied to those nuclear processes that occur in nature. Many of the ele-
ments have unstable isotopes that undergo spontaneous nuclear decay.
40
19
K
40
20
Ca +
0
-1
e
