The d Block

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Hi for Ca and V

Both Ca & V always lose the 4s electrons

For Ca

Hi(1) & Hi(2) relatively low as corresponds to removing outer 4s e-

Sharp increase in Hi(3) & Hi(4) cf Hi(2) due to difficulty in removing 3p e-

For Sc

Gradual increase from Hi(1) to Hi(4) as removing 4s then 3d e-

Slide 20

Oxidation States of TM’s

In the following table

Most important OS’s in boxes

OS = +1 only important for Cu

In all others sum of Hi(1) + Hi(2) low enough for 2e- to be removed

OS = +2, where 4s e- lost shown by all except for Sc and Ti

OS = +3, shown by all except Zn

Slide 21

Oxidation States of TM’s

Slide 22

Oxidation States of TM’s

No of OS’s shown by an element increases from Sc to Mn

In each of these elements highest OS is equal to no. of 3d and 4s e-

After Mn decrease in no. of OS’s shown by an element

Highest OS shown becomes lower and less stable

Seems increasing nuclear charge binds 3d e- more strongly, hence harder to remove

Slide 23

Oxidation States of TM’s

In general

Lower OS’s found in simple ionic compounds

E.g. compounds containing Cr3+, Mn2+, Fe3+, Cu2+ ions

TM’s in higher OS’s usually covalently bound to electronegative element such as O or F

E.g VO3-, vanadate(V) ion; MnO4-, manganate(VII) ion

Simple ions with high OS’s such as V5+ & Mn7+ are not formed

Slide 24

Stability of OS’s

Change from one OS to another is a redox reaction

Relative stability of different OS’s can be predicted by looking at Standard Electrode Potentials

E values

Slide 25

Stability of OS’s

General trends

Higher OS’s become less stable relative to lower ones on moving from left to right across the series

Compounds containing TM’s in high OS’s tend to be oxidising agents e.g MnO4-

Compounds with TM’s in low OS’s are often reducing agents e.g V2+ & Fe2+

Slide 26

Stability of OS’s

General trends (continued)

Relative stability of +2 state with respect to +3 state increases across the series

For compounds early in the series, +2 state highly reducing

E.g. V2+(aq) & Cr2+(aq) strong reducing agents

Later in series +2 stable, +3 state highly oxidising

E.g. Co3+ is a strong oxidising agent, Ni3+ & Cu3+ do not exist in aqueous solution.