The two most common isotopes of uranium are 235U and 238U .

(a) Compare the number of protons, the number of electrons, and the number of neutrons in atoms of these two isotopes.

(b) Using the periodic table in the front inside cover, write the electron configuration for a U atom.

(c) Compare your answer to part (b) to the electron configuration given in Figure. How can you explain any differences between these two electron configurations?

(d) 238U undergoes radioactive decay to 234Th How many protons, electrons, and neutrons are gained or lost by the 238U atom during this process?

(e) Examine the electron configuration for Th in Figure.Are you surprised by what you find? Explain.

FIGURE gives, for all the elements, the ground-state electron configurations for the valence electrons. You can use this figure to check your answers as you practice writing electron configurations. We have written these configurations with orbitals