Transition elements Flashcards
Define transition element
d-block elements that have an ion with an incomplete d sub-shell
What are 4 characteristic properties of transition metals?
- formation of coloured ions
- act as catalysts
- variable oxidation states
- form complex ions
describe, including ionic equations, the simple precipitation reactions and the accompanying colour changes of Cu2+(aq), Co2+(aq), Fe2+(aq) and Fe3+(aq) with aqueous sodium hydroxide;
Cu2+ + 2OH- –> Cu(OH)2
blue —> blue precipitate
Co2+ + 2OH- –> Co(OH)2
pink —-> blue ppt. , beige on standing
Fe2+ + 2OH- –> Fe(OH)2
pale green —> green precipitate
Fe3+ + 2OH- –> Fe(OH)3
yellow —> brick red ppt
explain the term ligand
a small molecule that can donate a lone pair of electrons to a central metal ion to form a coordinate bond
shapes of complex ions
octahedral e.g. [Cu(H2O)6]2+
tetrahedral e.g. [Cu(Cl)4]2-
square planner e.g. [Pt(NH3)2(Cl)2]
what is a bidentate ligand
e.g.
Has 2 lone pairs of electrons which it donates to the central metal ion forming 2 coordinate bonds
e.g. NH2CH2CH2NH2 ‘en’
types of stereoisomerism shown by complexes
optical: [Ni(NH2CH2CH2NH2)3]2+
cis/trans:
Ni(NH3)2Cl2
describe the use of complex ions in medicine
use of cis-platin as an anti- cancer drug and its action by binding to DNA in cancer cells, preventing division;
Ligand substitution:
aqueous copper with chloride ions
observations?
[Cu(H2O)6]2+ + 4Cl- [CuCl4]2– + 6H2O
blue –> green –> yellow
Ligand substitution:
aqueous copper with excess ammonia
observations?
Excess: [Cu(H2O)6]2+ + 4 NH3 —> [Cu(NH3)4(H2O)2]2+ _ 4H2O
blue –> dark blue
Ligand substitution:
aqueous cobalt with chloride ions
observations?
[Co(H2O)6]2+ + 4Cl- —> [CoCl4]2– + 6H2O
pink —> blue
what is Kstab?
the equilibrium constant for the formation of the complex ion in a solvent from its constituent ions
deduce the expression for the stability constant, Kstab, of a ligand substitution
M2+(aq) + 6X–(aq) MX64–(aq)
[MX64–(aq)]/[M2+(aq)][X–(aq)]6
What is the significance of a large Kstab value?
stable complex ion
more likely to form
bond angle in an octahedral complex ion
120 degrees
