1. The problem statement, all variables and given/known data Consider the beryllium (Be) atom. What are the possible terms and levels of the ground configuration 1s22s2 and the excited configuration 1s3p? Indicate any allowed transition between the levels. 2. Relevant equations Transitions allowed if ΔS = 0 (change in total spin) ΔL = 0 or ±1 (change in total angular momentum) ΔJ = 0 or ±1 (change in sum of total spin and angular momentum) 3. The attempt at a solution I didn't understand the notation of the excited states - why does it seem to have only two electrons? For 1s22s2, both shells are full, so L=0 and S=0. The configuration should be 1S For 1s3p, 1s has l=0 and s=1/2, while 3p has l=1 and s=1/2. So L=1 while S can be 0, 1/2 or 1. Thus the configurations are 1P, 2P, and 3P. I thought the only allowed transition was 1P to 1S. Am I thinking right?