Folks,
Unless I am mistaken, there are gross disagreements between Miessler & Tarr (5th ed) and the analyses by W. H. Eugen Schwarz (J. Chem. Ed. 2000, 435-443 and 444-448) about the energy levels of the valence orbitals in early transition metals and, subsequently, whether there are any electrons in 4s for the M+ ions.
A popular diagram (Figure 2.12) on p. 35 of M&T shows 4s below 3d up through vanadium and 1 electron in the 4s orbitals for each of Sc+, Ti+, Mn+, and Fe+.
Consistent with what is shown, the figure caption states "As a consequence, transition-metal ions with 2+ or greater charges have no s electrons, only d electrons in their outer levels."
On the following page (36), an italicized sentence is more general: "Transition metal cations have no s electrons, only d electrons in their outer levels." Unless there is a typo here (missing 'with 2+ or greater charges'[?]), by itself this seems to be a contradition.
Page 438 of the first Schwarz reference includes the sentence "The d shell becomes the lowest, dominant valence shell of the transition metals from group 3 onward; the so-called d-orbital collapse is complete in group 3."
On page 436 of the same (in the Table 1 Q&A), it states "(n-1)d is always occupied first in transition metal cations. The leading configuration of cations Mq+ of charges q from G [group number] through 0 is (n-1)dG-qns0. Only the chemically less important free neutral atoms in vacuum have an exceptional ns occupation."
In the subsequent Schwarz paper, on page 444 the energetic sequence of atomic orbitals is listed for K, Ca, and "Sc and subsequent":
K: 3p<<4s<4p<<3d<...
Ca: 3p<<4s<3d<4p<<...
Sc and subsequent: 3p<<3d<4s<4p<<...
A diagram on the same page, similar to that in M&T, shows 3d lower than 4s starting with Sc.
And I am remembering now a similar diagram in my old Shriver and Atkins - I am finding it on page 20 of the 4th edition (showing 3d lower than 4s beginning at Sc).
Am I missing something here? Does it have something to do with the fact that, in the p. 35 diagram, M&T is attempting to further show energy differences based on single vs. double occupancy?
I am currently looking a review from a POGIL activity I submitted for feedback that states "The titanium ground state energy diagram is incorrect. The 4s orbital should be lower than 3d in the ground state (Meissler + Tarr, 35)."
I would LOVE IT if someone who understands this material better than I do could straighten me out here.
Thanks as always.
- Joe
This one is a challenge to explain because it is difficult to rationalize the balances of contributions. Atkins's Phys chem 11th 8.b.3 (b) p 322 in the full book has some explanations. Scarri has written explanations also.
The 4s and 3d levels are close in energy. The ground states can be experimentally determined.
According to NIST, Sc ii, the atomic spectroscopy name for what chemists call Sc+ (21 electrons), the ground state is 3D. This is an electron configuration of [Ar]4s13d1, with the electron spins parallel. The same link also indicates that the [Ar]3d2 configuration (3F term symbol) is ~4800 cm-1 higher in energy. Sc iii (Sc2+) is 2D = 3d1.
According to NIST Ti+ (Ti ii in atomic spectroscopy lingo), is 4F (4s13d2). The 3d3 "state" (also 4F ) is about 900 cm-1 higher in energy. It is unclear to me how one would distinguish the two 4F states experimentally.
According to NIST V+ (V ii) is 3d4 with 4s1 3d3 2600 cm-1 higher energy. I did not check with the NIST data, but I expected the remaining of the 3d transition metals follow the expected pattern (all electrons in d)..
So, it seems like the details of the +1 section of the M&T p35 figure (from Rich 1965) appears to match the energy order implied by the NIST values.
-david