5.3.1 Transition elements Flashcards
why do transition metal elements form certain characteristics
due to incomplete d sub-level in ions
characteristics of transition metals
formation of coloured ions
variable oxidation states
catalytic activity
complex ion formation
which elements aren’t classed as transition elements
zinc
scandium
why is zinc not classed as a transition metal
Zn can only form a 2+ ion
in this ion Zn2+ has a complete d orbital and so doesn’t meet the criteria of having an incomplete d orbital in one of its ions
why is scandium not classed as a transition metal
Sc can only form 3+ ion, in this ion Sc3+ has an empty d orbital so doesn’t meet the criteria of having an incomplete d orbital in one of its ions
3 typical properties of transition elements
existence of more than one oxidation state in its compounds
form coloured ions
behave as catalysts
existence of more than one oxidation state in its compounds
e.g. iron normally forms +2 and +3
chromium can form +2 +3 +6
form coloured ions
the colours can vary depending on the oxidation state
behaviour as catalysts
iron in haber process to make ammonia
manganese dioxide to decompose hydrogen peroxide
complex ion definition
central metal ion surrounded by ligands
ligand definition
an atom, ion or molecule which donate an electron pair
co-ordinate bonding
when shared pair of electrons in the covalent comes from only one of the bonding atoms
co-ordination number
number of co-ordinate bonds formed to a central metal ion
what can ligands be
unidentate
bidentate
multidentate
unidentate
form one co-ordinate bond per ligand
H2O, NH3 and Cl-
bidentate
two atoms with lone pairs and can form two co-ordinate bonds per ligand
NH2CH2CH2NH2 and ethanedioate ion C2O4 2-
multidentate
can form multiple bonds per ligand
EDTA4- can form 6
EDTA4-
6 donor sites (4O and 2N)
forms a 1:1 complex with metal (11) ions
what shape complexes do transition metals form with small ligands
octrahedral
with H2O and NH3
what shape complexes do transition metals form with larger ligands
tetrahedral
with Cl-
what shape is cisplatin
square planar
what shape does Ag+ normally form
linear
what types of stereoisomerism can complexes show
cis-trans and optical
cis isomerism
normally known as Z isomers
on zee-zame-zide
trans isomerism
normally known as E isomers
complexes with 3 bidentate ligands
can form 2 optical isomers
non-superimposable mirror images
use of cisplatin
anticancer drug
how does cisplatin work
binds to the DNA of cancer cells and stops cancer cells dividing
causes cell apoptosis
reactions with excess NH3
ligand substitution
occurs with several transition aqueous ions
[Cu(H2O)6]2+ + 4NH3 -> [Cu(NH3)4(H2O)2]2+ +4H2O
blue to deep blue
why is ligand substitution with Cu incomplete?
as not all the water molecules are substituted
ligand exchange Co and Cr with excess NH3
NH3 and H2O are similar in size and are uncharged
so ligand exchange occurs without change of co-ordination number
ligand reactions with chloride ions
addition of a high conc of chloride ions (from a conc chlorine containing acid) to an aqueous ion leads to a ligand substitution reaction
in Cu and Co changes coordination number from 6 to 4
why in reactions with chloride ions can co-ordinate number change
because the Cl- ligand is larger and charged compared to H2O and NH3
copper reaction with chloride ions
[Cu(H2O)6]2+ + 4Cl- -> [CuCl4]2- + 6H2O
blue to yellow/green
cobalt reaction with chloride ions
[Co(H2O)6]2+ + 4Cl- -> [CoCl4]2- + 6H2O
pink to blue
what is formed if solid metal chloride is dissolved in water
aqueous [METAL(H2O)6]2+ complex rather than the
chloride [METALCl4]2-
biological complexes
iron 2 ion in haemoglobin
haem is an iron 2 complex with a multidentate ligand
O2 bonds to Fe2+ ions in the haemoglobin
CO is toxic to humans as it forms a strong coordinate bond with haemoglobin, stronger than with oxygen so prevents the binding
what are the ions involved in the precipitation reactions with sodium hydroxide and ammonia
Cu2+ Mn2+ Fe2+ Fe3+ Cr3+
basic form of the full equation for ppt reactions with NaOH
[metal (H2O)6] ^metal charge + 2OH- -> metal (H2O)6- charge of metal(OH)charge of metal + charge of metal H2O
copper ppt reaction with NaOH
Cu2+ (aq) + 2OH- -> Cu(OH)2 (s)
blue solution to blue ppt
ppt is insoluble in excess sodium hydroxide
manganese ppt reaction with NaOH
Mn2+ (aq) + 2OH- (aq) ->Mn(OH)2 (s)
very pale pink solution to pale brown ppt, darkens when in contact with air
ppt is insoluble in excess sodium hydroxide
iron(II) ppt reaction with NaOH
Fe2+(aq) +2OH- (aq) ->Fe(OH)2 (s)
pale green solution to green ppt
ppt insoluble in excess but in contact with air will turn brown as Fe(II) is oxidised to Fe(III), orange-brown
Fe(OH)2 (s) -> Fe(OH)3 (s)
iron (III) ppt reaction with NaOH
Fe3+ (aq) + 3OH- (aq) -> Fe(OH)3 (s)
pale yellow to orange-brown
ppt is insoluble in excess sodium hydroxide
chromium (III) reaction with NaOH
Cr3+ (aq) +3OH- (aq) -> Cr(OH)3 (s)
violet to grey-green ppt
is soluble in excess and will form dark green solution
Cr(OH)3 (s) + 3OH- (aq) -> [Cr(OH)6]3+ (aq)
What happens to copper and chromium in excess ammonia
Their hydroxide ppts will dissolve
Chromium in excess ammonia
Cr(OH)3(H2O)3 (s) + 6NH3 (aq) -> [Cr(NH3)6]3+ (aq) +3H2O (l) + 3OH- (aq)
Cr becomes [Cr(NH3)6]3+ purple solution
Copper in excess ammonia
Cu(OH)2(H2O)4 (s)+ 4NH3 (aq) -> [Cu(NH3)4(H2O)2 (aq) +2H2O (l) + 2OH- (aq)`
Becomes deep blue
Which electrons do transition elements lose first
Their 4s before the 3D
Iron (II) oxidation
Easily oxidized to Fe3+ green -> brown, normally use potassium manganate (VII) but oxygen in air also works
MnO4- (aq) + 8H+(aq) + 5Fe2+ (aq) -> Mn2+ (aq) +4H2O (l) + 5Fe3+ (aq)
Purple to colourless
Iron (III) reduction
Brown to green using potassium iodide
Brown colour of iodine can mask the colour change
2FE3+ (aq) + 2I- (aq) -> I2 (aq) + 2Fe2+ (aq)
Reducing chromium
Cr3+ (green) and Cr2+ (blue) commonly formed by reduction of Cr2O7 2- (orange) by strong reducing agent zinc in HCl acid solution. Fe2+ is a less strong reducing agent so will only reducing dichromate to Cr3+
Cr2O7 2- + 14H+ + 6Fe2+ -> 2Cr3+ + 7H2O + 6Fe3+
Orange to green
Oxidizing chromium
Alkaline chromium (III) can be oxidized using hydrogen peroxide, easier to oxidize a negative ion Chromium after being in excess NaOH
Cr(OH)6 3- (aq) —-(H2O2)—> CrO4 2- (aq)
Green to yellow
Reduction in this reaction: H2O2 + 2e- -> 2OH-
Reduction of Cu2+ to Cu+
Potassium iodide
Copper (II) is blue
2Cu2+ (aq) + 4I- (aq) -> I2 (aq) + 2CuI (s)
Brown solution and white ppt
Disproportionation of copper(I) ions
When reacting with sulfuric acid will disproportionate to Cu2+ and Cu metal
2Cu+ -> Cu + Cu2+
Full equation: Cu2O + H2SO4 -> CuSO4 + Cu + H2O
