15. Transition metals
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Define what is meant by a transition metal
Transition metals are d - block elements that form one or more stable ions with incompletely filled d orbitals
What are the properties of transition metals
Act as catalysts Variable oxidation states Form complex (mostly colored) ions
What color is VO2 +, with the oxidation number of vanadium as +5
Yellow
Why is scandium not a transition metal
It only forms the ion Sc3+ which has the configuration [Ar] 3d^0. It has an empty d shell.
Why do transition metals show various oxidation states
The 4s and 3d orbitals are very close in energy level. This means electrons can be lost from both 4s and 3d relatively easily. And the remaining electrons can form different stable configurations
Why is Zinc not a transition metal
It only forms a Zn2+ ion, so has the electron configuration [Ar] 3d^10. It has a full d shell.
What color is V3+
Green
What color is VO 2+, with the oxidation number of vanadium as +4
Blue
What can be used to reduce vanadium from +5 in VO2 + to +2 in V2+
Zinc
What color is V2+
Purple
Define what is meant by the term ligand
a species that has a lone pair of electrons, which it can donate into an empty d orbital of a metal ion to form a dative (coordinate) covalent bond
What are monodentate ligands, and give some examples
A ligand that has only a single bond with the central atom: Cl-, NH3, H2O, SCN-
Give 2 examples of bidentate ligands
1) 1,2 diaminoethane (also known as “en”) NH2CH2CH2NH2 2) ethanedioate ion (also known as “ox”) COO-COO- these have two lone pairs, so just one molecule of each forms two dative covalent bonds
Give the name of a hexadentate ligand
EDTA4- ion
Despite water having two lone pairs, why is it a monodenate ligand and not a bidenate ligand
Both lone pairs are on the same oxygen atom
How many chloride ions can bind to a complex metal ion
4
Give an example of a tetrahedral complex metal ion
Tetrachlorocuprate
What do you talk about when describing shapes of complexes formed from ligand substitution
Shapes of the complex (eg, octahedral, tetrahedral) Coordination number
Apart from a tetrahedral shape, what shape can complex ions with 4 coordinate bonds have?
Square planar (90°) –> most molecules that have a coordinate number of 4 are square planar, unless the ligand is a chloride ion when in that case its tetrahedral
When does cis platin occur
When the two chloride ligands are next to each other on one side (eg left) and the amine groups are next to each other on the other side. 90 degrees Platinum is in the middle
What shape is cis platin, what is its overall charge, and so what is the oxidation state of platinum
Square planar, 90 degrees Neutral overall So Pt is 2+ as it is cancelled out by 2 Cl-. (NH3 is neutral)
When does trans platin occur
When the chloride ligands are 180 degrees apart
Give the compound involved in cancer therapy’s
Cis platin Cis-platin distorts DNA, so it is more effective against cancer cells as they replicate rapidly (although it does also affect other rapidly-replicating cells). - As it targets a chiral molecule, only the cis isomer is in the correct orientation to have the desired effect, so trans-platin cannot used
Give the products and colour changes involved in the following reaction: [Cu(Η2Ο)6]2+ 4Cl- ⇌
[Cu(Η2Ο)6]2+ 4Cl- ⇌ [CuCl4]2- + 6H2O Pale blue –> yellow. However, it can often look green as reaction is in equilibrium This is a ligand substitution reaction There is a change in coordination number from 6 to 4, and change in shape from octahedral to tetrahedral