Explanation:
First, a quick revision of radioactive decay:
During alpha decay, an alpha particle is emitted from the nucleus —- it is the equivalent of a helium atom (i.e. it has a mass of 4 and an atomic number of 2). So, let's take the following question:
Polonium-210 is a radioisotope that decays by alpha-emission. Write a balanced nuclear equation for the alpha decay of polonium-210.
In symbols, the equation becomes
210/84Po--->?+4/2HE
The sums of the superscripts and of the subscripts must be the same on each side of the equation.
Take 4 away from the mass number (210-4 = 206)
Take 2 away from the atomic number (84-2 = 82). Lead is element number 82.
So, the equation is
210/84 Po--->206/82Pb+4/2He
Now let's try one for beta decay — remember that, in beta decay, a neutron turns into a proton and emits an electron from the nucleus (we call this a beta particle)
Write a balanced nuclear equation for the beta decay of cerium-144)
In nuclear equations, we write an electron as 0^-1e.
144/58Ce-->144/59Pr+^0-1e
Here's a fission reaction.
A nucleus of uranium-235 absorbs a neutron and splits in a chain reaction to form lanthanum-145, another product, and three neutrons. What is the other product?
We write a neutron as 1/0n, so the equation is
235/92U +1/0n--->145/57La+X+3 1/0n
Sum of superscripts on left = 236. Sum of superscripts on right = 148. So X
must have mass number = 236 – 148 = 88.
Sum of subscripts on left = 92. Sum of subscripts on right = 57. So X
must have atomic number = 92 – 57 = 35. Element 35 is bromine.
The nuclear equation is
235/92U+1/0n--->145/57La+88/35Br+31/0N
