D Block Elements: Looking at scandium to zinc of period 4 of d block. All d block are metallic, so
high MP, shiny, conduct electricity and heat. The highest energy sub-shell is a d sub-shell.
Electron Configuration: Electrons added to 3d orbitals from 1 to 10. Electrons occupy orbitals in
order of increasing energy. Remember 4s sub shell has lower energy than 3d so d block elements
fill AND empty 4s sub shell first before 3d.
Chromium and Copper: Half-filled d5
sub shell in chromium and fully filled d10 sub shell in copper
gives additional stability. So chromium and copper do not follow expected electron
configurations of placing electrons singly in 4s first, before pairing. Missing d4 and d9.
Learn below.
Transition Elements: Transition element has at least one ion
with partially filled d- orbital. Scandium and zinc are d block elements but not transition
elements.
Scandium: Scandium only forms Sc3+, 1s2
2s2
2p6
3s2
3p6
. Sc3+ has empty d- orbitals, not partially
filled.
Zinc: Zinc only forms Zn2+, 1s2
2s2
2p6
3s2
3p6
3d10. Zn2+ has full d- orbitals, not partially filled.
Properties of Transition Metals + Their Compounds: Need to know examples.
– Forming compounds where transition elements have more than one oxidation states.
– Forming coloured compounds.
– Elements and compounds are catalysts.
Variable Oxidation States: The number of oxidation states increases to manganese and then
decreases with no gaps.
– All transition elements form compounds with oxidation number +2 and 3+ (loss of two/
three electrons).
– A species containing transition element in high oxidation state is strong oxidising agent.
NFCC MC MCF
Must know these colours above.
In question they may give colour of precipitate, this gives a hint to what charge the metal ion
has. E.g. whether pale green Fe2+ or pale yellow Fe3+.
Orange solution created by Cr2O7
2- and not just Cr7+
.
Remember Roman numeral also gives charge.
Coloured Compounds: Solid compounds and ions of transition elements dissolve in water to
form coloured solutions. Colour varies with oxidation states.
Potassium dichromate (VI) is orange and Cr3+ is green. Cobalt (II) chloride is pink. Hydrated
copper (II) sulphate is blue. Fe2+ in solution is pale green and Fe3+ in solution is yellow.
Catalysts: Catalyst increases rate of chemical reaction.
– Hydrogenation of alkenes uses nickel catalyst to form alkane.
– Decomposition of 2H2O2 into 2H2O and O2 using MnO2 catalyst.
– Zinc reacts with acid, catalysed by Cu2+
.
– Fe in Haber process 3H2 + N2 <-> 2NH3.