Question

Polonium-210 decays once before it becomes a stable atom. What is that stable atom? ___

Answer 1

Answer:

$_{82}^{206}\text{Pb}$

Explanation:

All isotopes with atomic numbers from 83 up are unstable.  

Thus, $_{84}^{210}\text{Po}$must lose at least two protons to become stable. The only common type of decay that fits is α decay, the loss of a $_{2}^{4}\text{He}$ particle.

The nuclear equation is then

$_{84}^{210}\text{Po}\rightarrow _{x}^{y}\text{Z} + _{2}^{4}\text{He}$

The main point to remember in balancing nuclear equations is that the sums of the superscripts and the subscripts must be the same on each side of the equation.  

Then

84 = x + 2, so x = 84 - 2 = 82

210 = y + 4, so y = 210 – 4 = 206

Element 82 is lead, so the nuclear equation becomes

$_{84}^{210}\text{Pu} \longrightarrow _{82}^{206}\text{Pb} + _{2}^{4}\text{He}$