Transition Metals Flashcards
define transition metals
a d-block element which has at least one stable ion with an incomplete d- subshell
why are Scandium and Zinc not transition metals?
Sc3+ have no electrons in the 3d subshell
Zn2+ have a full 3D subshell
why are transition metal ions coloured?
- colours arise from d- electrons absorbing energy from visible light at particular wavelengths
- the d-electrons are promoted from the lower energy level to the higher energy level
- the wavelengths of light not absorbed by the solution are transmitted through it and absorbed by the human eye
- the solution has a colour corresponding to these transmitted wavelengths
where does the colour of a transition metals result from?
- most TM are coloured
- colours result from movement of electrons from partially filled d-orbitals
- if a compound has no electrons in the d orbital, it appears colourless
why are 4s electrons lost before 3d?
4s subshell is higher in energy
-
what is the relationship between oxidation state and oxidising power? + eg
-higher oxidation state= readily accept electrons (be reduced) = makes them powerful oxidising agents
E.g.
Mn7+ in potassium permanganate (VII) and Cr6+ in potassium dichromate (VII) (K2Cr2O7)
what is a disproportionation reaction?
one where a species is both oxidised and reduced in the same reaction
whats a catalyst?
speeds up reaction by providing an alternative reaction route and is not used up or chemically changes in the process
why are TMs able to act as catalysts?
because of their variable oxidation states
E.g. Fe is the catalyst used in the Haber Process
advantages + disadvantages of catalysts?
+
used in industry to speed to reactions pr to make them more energy- efficient
-
they can be toxic or damaging to the environment so when no longer needed, they must be disposed of carefully
define complex
a central metal atom or ion surrounded by ligands
define ligand
a molecule or ion that forms a co-ordinate bond with a transition metal by donating a lone pair of electrons
define coordinate number
the number of co-ordinate bonds to the central metal atom or ion
define monodentate ligand + give 3 common ones
a molecule or ion that can donate just one lone pair of electrons forming 1 co-ordinate bond
water :OH2 neutral charge
ammonia :NH3 neutral charge
chloride :Cl- charge = -1
define multidentate + give common ones
a molecule or ion that can donate multiple lone pairs o electrons from different atoms within the ligand, forming multiple coordinate bonds
ethane-1,2-diamine NH2Ch2CH2NH2 is a bidentate ligand 2lp often referred to as ‘en’
ethanedioate C2O42- is bidentate, 2lp
DTA is hexadentate, its present as EDTA 4- in complexes and has 6lp. Its a chelating agent + used in detergents, food and medicine
although Zn and Cu are next to each other in the periodic table why is copper (II) sulfate solution blue whilst zinc (II) sulfate solution colourless?
this is because Cu2+ has a partially filled d- subshell whereas Sn2+ doesn’t
what is the equation for calculating the difference in energy (energy gap)?
ΔE = hv = hc/λ ΔE= difference in energy (J) h= Planck's constant (6.63 *10^-34 Js) v= frequency of light absorbed (s-1 or Hz) c= speed of light in vacuum (3.00 * 10^8 ms-1) λ= wavelength of light absorbed (m)
what are some factors effecting the magnitude of ΔE and therefore the colour of the complex?
- the ligand
- oxidation state
- co-ordination number
how do you find the conc of transition metals in solution?
simple colorimetry
1- the absorbance of solutions of known concentrations is measured using the colorimeter
2-a calibration curve (absorbance vs conc graph) is produced
3-the absorbance of the solution of unknown conc is measured, and the calibration curve is used to find its conc
what is the chelate effect?
its an entropically driven process where multidentate ligands replace monodentate ligands in complexes (EDTA replacing H2O)
-its always more favourable for a TM ion to exchange monodentate ligands for those which can form more co-ordinate bonds
what needs to happen for a reaction to be thermodynamically feasible? how
the Gibbs free energy chnage must be negative and for it to be negative, there needs to a large increase in entropy for example making 7 molecules from 2
what does ΔG (Gibbs free energy) depend on?
enthalpy change, entropy change and temp of the reaction
whats the equations for ΔG (Gibbs free energy)?
ΔG = ΔH - TΔS ΔG = Gibbs free energy (Jmol-1) ΔH = enthalpy change (Jmol-1) T = temperature (K) ΔS = entropy change (J K-1 mol-1)
colours + electron config of Fe (II) and Fe (III)?
green = Fe(II)
1s2,2s2,2p6,3s2,3p6,4s2,3d6
pale brown = pale brown
1s2,2s2,2p6,3s2,4s2,3d5
what are the 2 types of stereoisomers in TM?
cis-trans isomers (E/Z) optical isomers (non superimposable images
define ligand substitution reactions
when a ligand in a complex is replaced by a different ligand that forms stronger co-ordinate bonds
why does the ligand substitution of H2O for NH3 occur? is there a chnage in coordination number?
no chnage in coordination number as the ligands are similar in size.
the exchange occurs because NH3 is a better ligand and forms stronger co-ordinate bonds than H2O
whats the colour of Aqueous copper (II) solution? what happens when you add small amounts of ammonia and also excess amounts of ammonia? Does the coordination number change?
-contains pale blue [Cu(H2O)6]2+ complex
-adding small amounts o ammonia, the ammonia acts as base, accepts protons form the H2O forming blue copper hydroxide precipitate
[Cu(H2O)6]2+ (aq) + 2NH3 (aq) → [Cu(OH)2(H2O)4] (s) + 2NH4+ (aq)
-adding excess ammonia, the precipitate dissovolves and the ammonia replaces the OH- and 2 of the H2O in a ligand sub reaction forming deep blue solution
[Cu(OH)2(H2O)4] (s) + 4NH3 (aq) ⇌ [Cu(NH3)4(H2O)2]2+ (aq) + 2H2O (l) + 2OH– (aq)
overall reaction as equilibrium = [Cu(H2O)6]2+ (aq) + 4NH3 (aq) ⇌ [Cu(NH3)4(H2O)2]2+ (aq) + 4H2O (l)
-coordination number= 6 and doesn’t change. This ligand sub is said to be incomplete as only four of the original 6 ligands are replaced
whats the colour of aqueous cobalt (II) + what happens when you add excess ammonia + does the coordination number change?
-[Co(H2O)6]2+ = pink complex
-excess ammonia replaces the H2O ligands forming straw coloured solution
[Co(H2O)6]2+ (aq) + 6NH3 (aq) ⇌ [Co(NH3)6]2+ (aq) + 6H2O (l)
co-ordination number= 6 and doesn’t change. this ligand sub is said to be complete as all of the original 6 ligands are replaced
what happens when aqeuous copper (II) mix with HCl?
sub of H2O with Cl- ligand
-Cl- ligand is bigger so co-ordination number decreases from 6 to 4
colour change from pale blue to green to yellow solution the green is from the mixing of yellow and blue
[Cu(H2O)6]2+ (aq) + 4Cl– (aq) ⇌ [Cu(Cl)4]2– (aq) + 6H2O (l)
what happens aqeuous copper mixes with HCl?
from pink to blue solution
[Co(H2O)6]2+ (aq) + 4Cl– (aq) ⇌ [CoCl4]2– (aq) + 6H2O (l)
what happens when aqueous iron (III) ions mix with HCl?
colour chnage from purple to yellow solution
[Fe(H2O)6]3+ (aq) + 4Cl– (aq) ⇌ [FeCl4]– (aq) + 6H2O (l)
how is tollens reagent formed? [Ag(NH3)2]+
and how does it work?
reacting ammonia solution with silver nitrate solution
-used to distinguish between aldehydes and ketones
Tollens oxidises aldehydes to carboxylic acids, reducing Ag+ to Ag forming a silver mirror inside of tube but not ketones
define heterogenous catalyst
a catalyst is in a different phase to the reactants.
the reaction occurs at active sites on the surface of the catalyst
how do heterogenous catalysts work?
1- adsorption -1+ reactants become attached to the surface of the catalyst
2- reaction-the weakening of bonds from adsorption cause the activation energy of the reaction to decrease so the reaction can occur
3-desorption- the product detaches from the catalyst
how do we minimise the cost of heterogenous compounds especially as they’re difficult to replace and you need to replace after impurities?
spread into a support medium and maximise SA
explain the Haber process
- used in industry to produce ammonia
- increases rate and makes it feasible at lower temps
- become contaminated with S + are replaced
explain the Contact process
-reactants at high temp + pressure so are in gas phase. The V2O5 catalyst is in the solid phase.
1-adsorption- SO2 absorbs onto V2O5
V2O5 (s) + SO2 (g) –> V2O4 (s) +SO3 (g)
2- V2O4 reacts with oxygen to regenerate the catalyst
V2O4 (s) + 1/2O2(g) –> V2O5 (s)
reabsorption: SO3 reabsorbs and diffuses away
define homogenous catalyst
a catalyst in the same phase as the reactants. the catalysts are always gaseous or in aqeuous solution and form an intermediate species during the reaction
