Question

Identify the unknown isotope X in the following decays.

Answer 1

Identify the unknown isotope in the given reactions by balancing atomic mass numbers and atomic numbers.

(a)

Given decay is,

In the above decay equation isotope decays as particle and nucleus, so, sum of Ra and alpha particle mass number is equal to mass number of isotope.

Now above equation changes as

So the element is Thorium.

Therefore, the unknown isotope X is.

(b)

Given decay is,

In this reaction, an electron is released, which is a beta particle. The electron is ejected from the nucleus in beta- minus decay.

Beta minus decay occurs when a neutron in the nucleus convert into the proton. So the atomic number of daughter nuclei is increased by 1. That is the atomic number of parent nuclei is less than 1 compared to the daughter nuclei.

So, the atomic number of unknown isotope in the equation is 81. From the periodic table, the element with atomic number 81 is Thallium (Tl).

Therefore, the unknown isotope X is.

(c)

Given decay is,

In this reaction, an electron is captured,. The electron is ejected by the nucleus.

Beta minus decay occurs when a proton in the nucleus convert into the neutron. So the atomic number of daughter nuclei is decreased by 1. That is the atomic number of parent nuclei is greater than 1 compared to the daughter nuclei.

So, the atomic number of unknown is 3. From the periodic table, the element with atomic number 3 is lithium (Li).

Therefore, the unknown isotope X is.

(d)

Given decay is

When a gamma particle is emitted, neither mass number nor atomic number changes.

Therefore, the unknown isotope X is.