Lanthanides: Electron Configuration & Oxidation States

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  • 0:00 Introduction to Lanthanides
  • 0:56 Electron Configuration
  • 4:40 Oxidation States
  • 10:01 Lesson Summary
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Lesson Transcript
Instructor: Saranya Chatterjee

Saranya has a masters degree in Chemistry and in Secondary Education. She has taught high school, AP chemistry for 2 years and is teaching undergraduate college chemistry for 3 years.

This lesson will provide the names and electron configuration of the fifteen lanthanides in the periodic table. It will also discuss the reason why they have a stable oxidation state of +3.

Introduction to Lanthanides

The f-block elements in the periodic table appear in two series characterized by the filling of the 4f and 5f orbitals. The first series contain the fourteen elements cerium to lutecium (elements 58 through 71) and are called lanthanides because they appear after lanthanum. The second series (thorium to lawrencium, elements 90 through 103) appears after actinium and are called actinides. The history of rare earth elements covers a long span of more than 113 years from 1774 (when yttrium was discovered) to 1907 (when lutecium was discovered) with promethium prepared artificially much later in 1926. The rare earth elements were first recognized as oxides and hence named ''earths''.

Electron Configuration

The ground state electron configurations of the lanthanides are provided in the table you're looking at on screen:

Name Symbol Atomic number Electron configuration
lanthanum La 57 (Xe)5d1 6s2
Cerium Ce 58 (Xe)4f1 5d1 6s2
Praseodymium Pr 59 (Xe)4f3 6s2
Neodymium Nd 60 (Xe)4f4 6s2
Promthium Pm 61 (Xe)4f5 6s2
Samarium Sm 62 (Xe)4f6 6s2
Europium Eu 63 (Xe)4f7 6s2
Gadolinium Gd 64 (Xe)4f7 5d1 6s2
Terbium Tb 65 (Xe)4f9 6s2
Dysprosium Dy 66 (Xe)4f10 6s2
Holmium Ho 67 (Xe)4f11 6s2
Erbium Er 68 (Xe)4f12 6s2
Thulium Tm 69 (Xe)4f13 6s2
Ytterbium Yb 70 (Xe)4f14 6s2
Lutetium Lu 71 (Xe)4f14 5d1 6s2

The ground state electron configuration of the lanthanide elements are generally of the type (Xe)4f n 6s2. Lanthanum is outside this generalization, but is included in the table for its uniform trivalency and other similarities. Among the lanthanides, exceptions to the 4f n 5d0 6s2 pattern are found in three cases.

Cerium, where the increase in effective nuclear charge after Lanthanum is insufficient to stabilize the 4f2 5d0 configuration compared to 4f1 5d1. The nuclear charge is insufficient to contract the 4f orbitals and lower their energy well below the 5d.

Gadolinium has the f7 d1 configuration, consistent with our expectation of a stabilized half-filled f shell.

Lutecium also has the f1 4d1 configuration where the last electron is added beyond the capacity of the 4f shell.

Oxidation States

Lanthanides are very prone to lose three electrons and form M3+ ion. Here's the explanation. We see that there is an electron in 5d shell in all lanthanides. But the Aufbau Principle, which states that in the ground state of an atom, an electron enters the orbital with lowest energy first and subsequent electrons are fed in the order of increasing energies, tells us that 5d gets filled up after 4f. The rule here is that one electron is added to Lanthanum in d shell and then the electrons start piling up in 4f shell in the consequent elements.

You see those 4f1 and 5d1 electrons in Ce. Since they are all alone in an orbital, they are pretty easy to remove. Orbitals tend to be stable when they are either completely filled, or exactly half filled. If an orbital is filled in a configuration which is not one of the above two, the electrons can be removed comparatively easily. The 4f and 5d electrons in Ce can be removed without much effort, which is why Ce shows both +3 as well as +4 state.

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