Can an element have a third energy shell without completely filling the second energy shell? I came across an electronic configuration diagram, it had three shells. The first shell had only one electron, the second had six and the third energy shell had five. An electron was also present outside all the shells.
Is this configuration possible?
Yes, it is possible. When an element is excited, some electrons from lower shell jumps to higher shells. For eg, in-ground state suppose an element has electronic configuration
$\ce{(1s)^2 (2s)^2 (2p)^5}$ . If we energize it, then some of the electrons jump up for a short period of time(till the energy is available) . The config becomes $\ce{(1s)^2 (2s)^1(2p)^6 }$.