Chapter 30, Problem 13Q

To determine

What happens to two extra electrons when Uranium decays to thorium, the thorium still have 92 electrons.

Answer to Problem 13Q

Solution:

The two extra electrons are not bounded tightly to the nucleus.

Explanation of Solution

When uranium having 94 electrons decays into a thorium which has 90 electrons ${}_{94}{}^{238}U\to {}_{90}{}^{234}Th+{}_2{}^{4}He$. But the daughter thorium nucleus may still have 92 electrons circling it. We know that thorium normally holds only 90 electrons. Thus there will be two extra electrons. These extra electrons held by thorium will be loosely held thus number of protons in nucleus have been reduced to 90 from 92. These two extra electron can escape from the thorium atoms by various mechanisms. These are free electrons and they don’t gain any energy from the decay.