Edexcel IAL Chemistry 17.13 octahedral six-coordinate complexes

For six-coordinate complexes, show six ligand donor pairs arranged as far apart as possible, then use wedge and dot bonds to make the 3D shape clear.

Exam points

Explain octahedral shape from six electron pairs arranged to minimise repulsion.
Draw six-coordinate complex ions using wedge, dot or displayed 3D bonds.
Write formulae such as [Cr(H2O)6]3+ when aqueous complex evidence is given.

[Maximum number: 2]

This question is about compounds and complex ions of iron.

In aqueous solution, iron(II) exists as the complex ion $\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$ .

Explain the shape of the $\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$ complex ion.

An explanation that makes reference to the following points:

- octahedral because there are six pairs of electrons

(1)

- which are as far apart as possible to minimise repulsion (1)

Allow this shown on a diagram
Allow octahedral because there are 6 coordinate bonds/coordination number is 6
Ignore just octahedral because there are 6 ligands
Do not award if bond angle other than $90^{\circ} /$ $90^{\circ}$ and $180^{\circ}$ stated
Allow repel/arrange/shape to maximum separation
Do not allow repulsion between atoms or water
molecules or ligands

(2)

Number

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17.13—Why complexes with six-fold coordination have an octahedral shape, such as those formed by metal ions with H2O, OH- and NH3 question 1