Transition Metals
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Define transition metals
A d block element with at least one ion with an incomplete d sub shell
Why is zinc not a transition metal?
Zn2+ is the only ion and has a full d subshel
Why is scandium not a transition metal?
Sc3+ is the only ion with no d electrons.
Define ligand
A molecule or ion with donates a lone pair in a co-ordinate bond with a transition metal. Eg. H2O, NH3, OH-, CN- etc
Define monodentate
Ligand that only donates one lone pair of electrons to the metal ion
Define bidentate
Ligand that donates two lone pair of electrons to the metal ion forming two co-ordinate bonds.
What are the common oxidation states of chromium?
+3 and +6
What are the common oxidation states of manganese?
+2, +4 and +7
What are the common oxidation states of iron?
+2 and +3
What are the common oxidation states of cobalt?
+2 and +3
What are the common oxidation states of copper?
+1 and +2
Why do transition metals have variable oxidation states?
The energies of the 4s and 3d orbitals are very similar and so the energy required to remove electrons (ionisation energy) is similar thus the energy to achieve higher oxidation states is very small. The oxidation state depends on the oxidising power of the atom it is reacting with.
What are the common characteristics of transition metals?
• Variable Oxidation States • Coloured Compounds • Catalyst
Why do transition metals form different coloured compounds?
When ligands appraoch a transition metal, the negative charge density of the lone pairs repel the electrons in the d orbitals changing their energies making them no longer degenerate. The d orbitals split into different energy levels: 3 lower energy and 2 higher energy. The gap between the orbitals determines the amount of energy required to promote an electron. As the metal absorbs certain frequencies in the visible region of the electromagnetic spectrum. The unabsorbed frequencies are seen by the eye.
What does degenerate in d orbitals mean?
Having the same energy level.
What colour are Copper(II) (Cu2+) metal ions in solution?
Pale blue
What colour are iron(II) (Fe2+) metal ions in solution?
Pale green
What colour are iron(III) (Fe3+) metal ions in solution?
Red/brown
What colour chromate (CrO4-) metal ions in solution?
Yellow
What colour manganate (MnO4-) metal ions in solution?
Purple
What colour are dichromate (Cr2O7-) metal ions in solution?
Orange
What colour are Cobalt(II) (Co2+) metal ions in solution?
Pink
What colour are Chromium(III) (Cr3+) metal ions in solution?
Green
Why do transition metals and their compounds make good catalysts?
• Variable oxidation states allows them to form intermediate compounds with lower activation energies as the catalyst can oxidise/reduce the reactant making them more reactive. Typical in homogenous catalysts. • Partially filled d orbitals allows them to form co-ordinate bonds, increasing the reactivity of the series bonded to the metal or bringing reactants closer togehter increasing the frequency of successful collisions. • Provide a good surface as reactants are adsorbed(stick/adhere) onto the surface of the metal and bonds are weakened. The products of this reaction are desorbed from the surface. Typical of heterogenous catalysts.