The oxidation state of an element is related to the number of electrons that an atom loses, gains, or appears to use when joining with another atom in compounds. It also determines the ability of an atom to oxidize (to lose electrons) or to reduce (to gain electrons) other atoms or species. Almost all of the transition metals have multiple oxidation states experimentally observed.

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Introduction

Filling atomic orbitals requires a set number of electrons. The s-block is composed of elements of Groups I and II, the alkali and alkaline earth metals (sodium and calcium belong to this block). Groups XIII through XVIII comprise of the p-block, which contains the nonmetals, halogens, and noble gases (carbon, nitrogen, oxygen, fluorine, and chlorine are common members). Transition metals reside in the d-block, between Groups III and XII. If the following table appears strange, or if the orientations are unclear, please review the section on atomic orbitals.

Table \(\PageIndex{1}\) s Orbital p Orbitals d Orbitals
1 orbital, 2 electrons 3 orbitals: px, py, pz; 6 electrons 5 orbitals: dx2-y2, dz2, dxy, dyz, dxz; 10 electrons
Highest energy orbital for a given quantum number n Degenerate with s-orbital of quantum number n+1

The key thing to remember about electronic configuration is that the most stable noble gas configuration is ideal for any atom. Forming bonds are a way to approach that configuration. In particular, the transition metals form more lenient bonds with anions, cations, and neutral complexes in comparison to other elements. This is because the d orbital is rather diffused (the f orbital of the lanthanide and actinide series more so).


Neutral-Atom Electron Configurations

Counting through the periodic table is an easy way to determine which electrons exist in which orbitals. As mentioned before, by counting protons (atomic number), you can tell the number of electrons in a neutral atom. Organizing by block quickens this process.For example, if we were interested in determining the electronic organization of Vanadium (atomic number 23), we would start from hydrogen and make our way down the the Periodic Table).

1s (H, He), 2s (Li, Be), 2p (B, C, N, O, F, Ne), 3s (Na, Mg), 3p (Al, Si, P, S, Cl, Ar), 4s (K, Ca), 3d (Sc, Ti, V).

If you do not feel confident about this counting system and how electron orbitals are filled, please see the section on electron configuration.

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​​​​​​Multiple Oxidation States

Most transition metals have multiple oxidation states, since it is relatively easy to lose electron(s) for transition metals compared to the alkali metals and alkaline earth metals. Alkali metals have one electron in their valence s-orbital and their ionsalmost alwayshave oxidation states of +1 (from losing a single electron). Similarly,alkaline earth metals have two electrons in their valences s-orbitals, resulting in ions with a +2 oxidation state (from losing both). However, transitions metals are more complex and exhibit a range of observable oxidation states due primarily to the removal of d-orbital electrons. The following chart describes the most common oxidation states of the period 3 elements.

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Summary

Oxidation states of transition metals follow the general rules for most other ions, except for the fact that the d orbital is degenerated with the s orbital of the higher quantum number. Transition metals achieve stability by arranging their electrons accordingly and are oxidized, or they lose electrons to other atoms and ions. These resulting cations participate in the formation of coordination complexes or synthesis of other compounds.

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Questions

Determine the oxidation states of the transition metals found in these neutral compounds. Note: The transition metal is underlined in the following compounds.

(A) Copper(I) Chloride: CuCl (B) Copper(II) Nitrate: Cu(NO3)2 (C) Gold(V) Fluoride: AuF5
(D) Iron(II) Oxide: FeO (E) Iron(III) Oxide: Fe2O3 (F) Lead(II) Chloride: PbCl2
(G) Lead(II) Nitrate: Pb(NO3)2 (H) Manganese(II) Chloride: MnCl2 (I) Molybdenum trioxide: MoO3
(J) Nickel(II) Hydroxide: Ni(OH)2 (K) Platinum(IV) Chloride: PtCl4 (L) Silver Sulfide: Ag2S
(M) Tungsten(VI) Fluoride: WF6 (N) Vanadium(III) Nitride: VN (O) Zirconium Hydroxide: Zr(OH)4
Determine the oxidation state of the transition metal for an overall non-neutral compound: Manganate (MnO42-) Why do transition metals have a greater number of oxidation states than main group metals (i.e. alkali metals and alkaline earth metals)? Which transition metal has the most number of oxidation states? Why does the number of oxidation states for transition metals increase in the middle of the group? What two transition metals have only one oxidation state?