transition metals Flashcards
what is a transition metal
a dblock element that forms at least one stable ion with partially filled d orbitals
what is a d block element
an element where it’s highest energy electrons are in a D subshell
why do chromium and copper only have 1 electron in 4s subshell
having a half-full, or entirely full, set of D orbitals is particularly stable
despite having a higher energy level than the 4s shell, the energy needed to promote an electron from 4s to 3d is less than the benefit of having a half full, or full, set of d orbitals
why can a transition metal form many different ions
there is a gradual increase in successive ionisation energies however they are very similar
how does a complex ion form
when a transition metal ion is surrounded by ions or other molecules that form coordinate bonds (ligands)
where do the electrons go in transition metal complex ions
into empty available D orbitals
what is a ligand
a molecule that can form coordinate bonds with a transition metal ion as it has a lone pair available to donate
why is a complex ion with 2 ligands linear
electron pairs in bonds are spaced out at maximum separation and minimum repulsion
why will a metal ion accept 6 water molecules as ligands but only 4 chloride ions as ligands
chloride ions have negative charge so they repel eachother
chloride ions are bigger than H2O so cannot fit 6 around metal ion at 90 degree angles
why are some complex ions with 4 ligands tetrahedral, and others square planar
square planar will occur if metal ion has lone pairs as there is increased repulsion on top/bottom
what is a monodentate ligand
a ligand that has 1 lone pair available for co-ordination to transition metal ions, as well as their shape
what is an example of a multidentate ligand
EDTA - 4- charge as has 4 letters
explain why complex ions are coloured
ligand causes D orbitals to split into higher and lower energy levels, different ligands cause different energy gaps
light passes through solution energy is absorbed, electrons promoted to high energy D orbitals
specific energy needed for energy gap is absorbed and all other light is transmitted in form of visible light
what can affect the colour of complex ions
transition metal ion (diff number of electrons)
charge of transition metal ion (diff number of electrons)
ligands (cause different splitting)
coordination number/shape
why is there a lack of colour in some complex ions
if d orbitals are full/empty electrons cannot move between the energy levels= no absorbance= no colour
coordination number meaning
number of coordinate bonds that exist in a complex ion
what shape do H2O OH- and NH3 ligands usually form
octahedral
what shape do Cl- ligands form
tetrahedral as they are larger ligands
when will square planar complexes form in complex ions
must have a lone pair on transition metal ion
what is an example of a square planar complex ion
cis/trans platin
why is cisplatin used in treatment of cancer and not transplatin
transplatin cannot form 2 coordinate bonds with adjacent nitrogenous bases (guanines) , it can only form 1 as chlorines are opposite eachother so DNA polymerase can easily break this bond and DNA can still replicate
how many coordinate bonds does EDTA make
6
what is the charge on EDTA
-4
what is haemoglobin
is an iron (II) complex containing a multidentate ligand
what is a ligand exchange reaction of haemoglobin
when an oxygen molecule is replaced by a carbon monoxide molecule
or when oxygen molecule replaces water molecule in lungs (breathe out water vapour)
2 examples of bidentate ligands
ethanedioate
ethane 1,2 diamine
is a more negative E cell value less or more stable
more stable
why might there be a difference in redox potential to standard databook values
depends on the environment the ions are in
why can Cr3+ be green or violet
when surrounded by water molecules Cr3+ is violet however Cl- impurities can substitute so that it is green
why does Cr2+ often not stay in that oxidation state
very unstable can be oxidised back to Cr3+ by oxygen in the air
what does amphoteric mean
something that acts as an acid or a base
why when you are making a chromium complex should you use nitrogen atmosphere
so oxygen in the atmosphere does not oxidise the Cr2+ back to Cr3+
describe the chelate effect
when we substitute monodentate ligands for bidentate/multidentate ones we create a solution with more particles in it so there is an increase in entropy, reaction is more likely to happen
why are transition metals such good catalysts
by recieving/ losing electrons in their d orbitals to act as intermediates
steps of heterogenous catalysts
1) reactants are adsorbed onto the surface of the catalyst
2) bonds weakened by interaction
3) reactants more likely to collide
4) orientation of molecules is favourable
5) reaction occurs on surface
6) products desorbed from surface
what is catalytic poisoning
some substances (impurities) can adsorb and not desorb so block active sites
Fe in haber process poisoned by S as methane for hydrogen often has sulfur impurities
Pt, Rh in catalytic converters poisoned by Pb
what does Fe do in haber process
weakens N2 triple bond when N2 adsorbs
what is autocatalysis
a reaction being catalysed by one of its products eg Mn2+
aqueous Cr3+
violet when surrounded by water but impurities make it green
Cr3+ with OH-
green precipitate
Cr3+ with excess OH-
green solution
aqueous Fe2+
green solution
Fe2+ with OH-
green ppt that turns brown on oxidation with air
aqueous Fe3+
yellow solution
Fe3+ with OH-
red brown ppt
aqueous Co2+
pink solution
Co2+ with OH-
blue ppt that turns pink on standing
aqueous Cu2+
blue solution
Cu2+ with OH-
blue ppt
Cr3+ with NH3 and excess
NH3 - green ppt
excess - violet solution (ligand exchange)
Fe2+ with NH3
green ppt
Fe3+ with NH3
brown ppt
Co2+ with NH3 and excess
NH3 - blue ppt
excess - yellow solution
Cu2+ with NH3 and excess
NH3 - pale blue ppt
excess - dark blue solution (complex ion has 4NH3 and 2H20)
what is an example of an amphoteric complex ion
chromium hydroxide ppt
Cu2+ plus Cl-
blue -> yellow solution
octahedral -> tetrahedral
Co2+ plus Cl-
pink -> blue solution
octahedral -> tetrahedral
2 examples of d block elements which aren’t transition metals
zinc and scandium
different aqueous chromium ion colours
dichromate - orange
chromate - yellow
3+ - green
2+ - blue
different aqueous manganese ion colours
MnO4 2- = green
MnO4 - = purple
Mn2+ = pink
what can you add to transition metal reactions to stop ions oxidising with the air
cotton wool
