A radioactive nucleus alpha decays to yield a sodium-24 nucleus in 14.8 hours. What was the identity of the original nucleus? Show the nuclear equation.

Question

cuanchi · Answer

an alpha particle is equal to a  He nucleus. It has two protons and 2 neutrons, then the mass of the nucleotide is 
$$_{2}^{4}He =_{2}^{4}\alpha  $$
 $$_{?}^{?}X \rightarrow _{11}^{24}Na + _{2}^{4}He $$

cuanchi · Answer

you have to find the reactant in this equation, the mass and the number of protons has to be the same in both sides of the equation
you add 24+4= 28
and 11+2= 13
the 13 atomic number is telling you what element it is and the 28 atomic mass is telling you what is the mass of the isotope of that element

arihangdu · Answer

Thanks you

arihangdu · Answer

X aluminum right?

cuanchi · Answer

yes, and the mass?

arihangdu · Answer

But in the period table it is Si with mass 28 right or

arihangdu · Answer

Al has only 26.982 in my table ...

cuanchi · Answer

No dear!!! that is the average mass proportional to the abundance of the different isotopes. In this problem you have only one of the isotopes of the Al. The mass is equal to the sum of the mass of the nucleoids In your case is 

$$_{13}^{28}Al$$

the isotope of the Al that has a mass of 28 
You are right Si can have also some isotope with a mass of 28 or the average mass is 28 but what tell you what element it is is the number of protons

arihangdu · Answer

Oke thank you my friend appreciate your help with good explanation.you are great.

cuanchi · Answer

Al has many isotopes https://en.wikipedia.org/wiki/Isotopes_of_aluminium

arihangdu · Answer

Okay thanks bye I don't want to kill more your time. Thanks you very much.byeeee great help for me