m5 - transition metals Flashcards
why are d block elements called d block
d is their outer (highest energy) sub shell
transition metal def
a d-block element that forms at least one stable ion with an incomplete d-subshell
electron configuration of transition metals
fill 4s2 shell first before 3d
EXCEPT in Cr and Cu
Cr ends in 3d5 4s1
Cu ends in 3d10 4s1
how many unpaired electrons does Cr have
6
which 2 are not transition elements
Sc and Zn
Sc only forms a 3+ ion in which the d subshell is empty
Zn forms only a 2+ ion in which the d subshell is full
so they don’t form any ions with a partially filled d subshell therefore not transition
transition metals being used as catalysts (2 examples)
iron in haber process
mno2 in decomposition of h2o2
what is a complex ion
a transition metal ion surrounded by (6) ligands
ligand def
molecule or ion with a lone pair of e- that’s able to form a dative (coordinate bond) to the central metal ion by donation of this e- pair
monodentate ligand examples and def
form one coordinate bond
h2o
nh3
cl-
bidentate ligands example and def
form 2 coordinate bonds
nh2ch2ch2nh2
coordination number def
no of coordinate bonds between central metal ion and it’s ligands
if there are 6 coordination bonds what shape is the molecule
octahedral
4 coordination bonds around a central atom is what shape
tetrahedral or square planar
stereoisomerism in complex ions, bond angle for cis is
90°
so (example Cl) are next to each other
stereoisomerism in complex ions, bond angle for trans is
180°
so (example Cl) are opposite each other
optical isomers hack
flip them so a mirror image
ligand substitution reactions and colour -> copper dissolving in water
(there are 2 reactions, one with cl one with nh3)
when dissolved in water = [Cu(H2O)6] 2+ + Cl-
water ligands can then be replaced by other ligands eg chloride from conc acid -> [CuCl4] 2-
blue => yellow
or 4 ammonias
[Cu(H2O)6] 2+ + 4NH3 -><- [Cu(NH3)4(H2O)2] 2+ + 4H2O
blue => deep blue
ligand substitution reaction and colour - chromium dissolving in water
forms [Cr(H2O)6] 3+ + NH3 -> Cr(OH)3 + excess NH3 -> [Cr(NH3)6] 3+
violet => purple
[Cr(H2O)6] 3+ + NaOH -> Cr(OH)3 + excess NaOH -> [Cr(OH)6] 3-
violet => green
reduction of Cu2+ to Cu+ using iodine ions
2Cu2+ + 4I- —> 2CuI + I2
inter conversion between Fe2+ and Fe3+ (oxidation and reduction)
pale green => yellow
oxidation reaction by something eg MnO4- or Cr2O7 2-
reduction reaction by something eg I- colourless —> red brown I2
inter conversion between Cr3+ and Cr2O7 2-
oxidation: green => orange in acidic conditions by oxidising agent
or green => yellow in alkaline OH- by H2O2
reduction: orange => green in acidic conditions by reducing agents eg Zn
biochemical importance of iron
haemoglobin has Fe2+ ion at centre (5 coordinate N ligands)
oxygen acts as a ligand and binds readily to it, carried to cells where it’s released (weak and reversible attraction)
oxygen ligands can be replaced by CO ligands which bind more strongly and irreversibly, reduces O2 around body, tissues starved of oxygen and die
colour of Cr3+ metal-aqua ion
violet solution
[Cr(H2O)6]3+
colour of Fe2+ metal aqua ion
green solution
[Fe(H2O)6]2+
colour of Fe3+ metal aqua ion
yellow solution
colour of Mn2+ metal aqua ion
pale pink solution
colour of Cu2+ metal aqua ion
blue solution
colour of Cr3+ with OH- (and then xs OH-)
green precipitate Cr(OH)3
xs: green solution [Cr(OH)6] 3-
colour of Fe2+ with OH-
green precipitate Fe(OH)2
colour of Fe3+ with OH-
brown precipitate Fe(OH)3
colour of Mn2+ with OH-
pale brown precipitate Mn(OH)2
colour of Cu2+ with OH-
blue precipitate Cu(OH)2
colour of Cr3+ with xs NH3
purple solution
[Cr(NH3)6] 3+
colour of Cu2+ with xs NH3
dark blue solution
[Cu(NH3)4(h2o)2] 2+
