DM Flashcards
electronic configuration of chromium
lower energy given by putting one electron in each 3d and 4s orbital, rather than 2 electrons in 4s
electronic configuration of copper
lower energy given by putting 2 electrons in each 3d orbital and one electron in 4s, rather than 9 electrons in 3d and 2 in 4s
transition metals form ions by losing electrons first from
the 4s orbital
transition metals forming ions
form one or more stable ion which have INCOMPLETELY FILLED D-ORBITALS
zinc and scandium as transition metals
often not considered transition metals
zinc only forms Zn (II) which has full d-orbitals
scandium only forms Sc (III) which has empty d-orbitals
potassium manganate (VII)
purple compound
can oxidise Fe (II) to Fe (III)
catalyst
alters rate of chemical reaction but remains chemically unchaged in the process
transition metals as catalysts
it is the availability of 3d and 4s electrons and the ability to change oxidation state that help make transition metals good catalysts
heterogeneous catalysis
catalyst in different physical state to reactants
transition metals can used 3d and 4s electrons to form weak bonds to reactants (chemisorption)
homogeneous catalysis
catalyst in same physical state as reactants
usually involves in transition metal ion forming an intermediate compound with one or more reactants
reaction of Fe (II), Fe (III) and Cu (II) with ammonia solution and NaOH
form copper (II) hydroxide, iron (II) hydroxide and iron (III) hydroxide
if source of OH- is ammonia solution, the copper (II) hydroxide precipitate will redissolve on addition of excess ammonia solution to form a purple-blue solution
effect of ligands on colour of compounds
there are 5 d orbitals in d-block metals
ligands cause these orbitals to split in such a way that some are slightly higher in energy level than other
the deltaE between the two levels is now such that the light absorbed falls in the visible part of the spectrum
transmitted light is the light that is not absorbed, and is the colour seen
monodentate ligand
can only form one dative/coordinate bond to central metal ion (eg. halides, cyanide, hydroxide)
ligands
negatively charged ions or neutral molecules possessing a lone pair of electrons
attach themselves to the central metal ion by using a lone pair of electrons to form a dative/coordinate bond
cause the five d orbitals to split into different energy levels
effect of concentration of solution on the light it absorbs and the colour it appears
more concentrated solution, more light absorbed, darker colour of solution
colorimetry
used to determine concentration of substance
narrow beam of white light passed through coloured filter
colour of filter must correspond to the colour of light most strongly absorbed (complimentary to colour of light emitted/seen)
potential difference
a measure of how much each electrode is tending to accept/release electrons
measured in Volts
one volt = one joule of energy tranferred per coulumb of charge
Ecell
the potential difference in an electrochemical cell when no current flows
difference in the elctrode potential of each half cell
more positive electrode potential of half cell
greater tendency to accept electrons (be reduced)
more negative electrode potential of half cell
lesser tendency to accept electrons
purpose of salt bridge between half cells
carry current between half cells
complete circuit
standard hydrogen half cell
used as a reference, all other half cells measured against it standard conditions (1 moldm-3 solution of H+ , 298K, platinum electrode, hydrogen gas bubbled into solution)
when no metal in half reaction, a electrode which is
unreactive is used (eg. platinum)
rust
a hydrated form of iron III oxide > Fe2O3.xH2O
process of rusting
when a water droplet is left in contact with iron/steel, the conc of dissolved oxygen in the water droplet determines which regions of the metal surface are sites of red or ox
at centre of droplet, oxygen conc is low so iron is oxidised
at edges of droplet, conc of dissolved O2 is higher, so oxygen is reduced to OH using electrons from oxidation of iron
Fe (II) and hydroxide react to form iron (II) hydroxide
iron (II) hydroxide is oxidised to hydrated iron (III) oxide
rusting equations
Fe (s) Fe (II) (aq) + 2e- [NEGATIVE ELECTRODE]
1/2(O2) (g) + H2O (l) + 2e- 2OH- (aq) [POSITIVE ELECTRODE]
sacrificial protection of iron
use metals with more negative electrode potential (eg. Zn or Cr)
sacrificial metal is oxidised so that iron is not, preventing formation of Fe (II)
complex
central metal atom/ion surrounded by ligands
may have a +ve charge, -ve charge or no charge
charged complex =
complex ion
coordination number
number of bonds from the central ion to its ligands
shapes relating to coordination number
6 - octahedral
4 - tetrahedral (sometimes square planar)
2 - linear
ligand substitution reaction
ligands can displace other ligands
this occurs if the new complex formed is more stable than the previous complex
therefore, stability of complex is dependent on its ligands
