Information ploen ons) with large numbers of electrons, the ordering of the ener
ID: 589612 • Letter: I
Question
Information ploen ons) with large numbers of electrons, the ordering of the energy levels gets quite ted Increased nuclear charge results in a lowering of energy for all orbitals, but the complicated agnude of the effect varies depending on both n and (. One reason for this is the variation in the effectiveness of the shielding for these different orbitals. For example, an electron in a . orbital is much less effectively screened from the nucleus than one in a 3d orbital because the 4 wavefunction has a much larger amplitude close to the nucleus. As atomic number increases, the energy of the 4s orbital is thus expected to become approximately equal to that of the 3d at some point. Exercises 1. Carefully explain why the 2p energy level in Li is at a higher energy than the 2s level in Li. That is, explain why the configuration 1s22s1 is lower in energy than 1s22p. 2. Briefly explain why the 2s and 2p energy levels are at the same energy for Li2+ 3. Explain why the ground state wavefunction of lithium is 123-9.(11s(2M-(3) and not 4,123-as (ng,(%, (3) . 4. Comment on the validity of this statement: To some extent, every electron shields the nuclear charge from every other electron 5. Write the expression for the classical electronic energy of a Be atom. Write the Hamiltonian operator for a Be atom. Write a trial function for the electrons in a Be atom.Explanation / Answer
1. The 2p energy level in Li atom is higher in energy than 2s level in Li.
This is quite obvious. According to the afbau principle, 2p is higher energy orbital than 2s. As it could be confirmed by (n+l) rule also. In case of 2p it is 3 whereas in case of 2s it is 2 only. So all these explains the 2p energy level is higher than 2s.
Now the 1s22s1 is lower in energy than 1s22p1 in Li.
Here also for Li ground state electronic configuration is: 1s22s1
and now if we provide some energy then only one electron will transfer from 2s-orbital to 2p- orbital. So that's why of course excited states are higher in energy than ground level.