Question

Predict whether each of the following nuclides is stable or unstable (radioactive). If the nuclide is unstable, predict the type of radioactivity you would expect it to exhibit.

(a)${}_{\mathbf{19}}{}^{\mathbf{45}}\mathbf{K}$

(b) ${}_{\mathbf{26}}{}^{\mathbf{56}}\mathbf{Fe}$

(c)${}_{\mathbf{11}}{}^{\mathbf{20}}\mathbf{Na}$

(d)data-custom-editor="chemistry" ${}_{\mathbf{81}}{}^{\mathbf{194}}\mathbf{Tl}$

Short answer

1. Unstable, beta decay
2. Stable
3. Unstable, positron production
4. Unstable, alpha decay

Step-by-step solution

Determining whether K1945 is stable or unstable

The most abundant isotope is usually considered the most stable isotope.

From the periodic table, we know that the molar mass of K is 39.1 g/mol. K with molar mass 45 is far from so many neutrons to be a stable isotope. Hence, it is unstable and can undergo beta decay to attain stability.

Determining whether Fe2656 is stable or unstable.

The molar mass of Fe is 55.8 g/mol, which is very close to 56. Hence, iron-56 is stable.

Determining whether Na1120 is stable or unstable.

From the periodic table, we know that the molar mass of Na is 23.0 g/mol. Na with molar mass 20 is way too less than the required neutrons to be a stable isotope. Hence, it is unstable and can undergo positron production to attain stability.

Also, as an alternative, electron capture can be taken into consideration.

Determining whether Tl81194 is stable or unstable.

From the periodic table, we know that the molar mass of Tl is 204.4 g/mol. Tl with molar mass 195 is way too less than the required neutrons to be a stable isotope. Hence, it is unstable and it can undergo alpha decay to attain stability since it is a heavy element.

Alternatives also include positron emission and electron capture.