transition metals p1 Flashcards
transition element
an element which forms at least one stable ion with a partially full d-shell of electrons
where are the transition metals located in the periodic table?
middle from Ti to Cu- part of the d-block
what are some characteristic physical properties of transition metals?
metallic, good conductors of heat and electricity, hard, strong, shiny, high mp and bp, low reactivity
uses of iron?
vehicle bodies, reinforce concrete
uses of titanium?
jet engine parts
uses of copper?
water pipes
what are the characteristic chemical properties of transition metals?
variable oxidation states –> take part in many redox reactions
coloured compounds/ions in solution
good catalysts
form complex ions
complex ion
central transition metal ion surrounded by ligands (other ions/molecules) that are co-ordinated bonded to it
examples of transition metal catalysts and the process/reactions they catalyse
iron - Haber process
Vanadium oxide - Contact process
MnO2 - decomposition of H2O2
which electrons do transition metals lose first when forming ions?
4s
ligand
an ion or molecule with at least one lone pair of electrons, that donates them to a transition metal ion ton form a co-ordinate bond and thus a complex ion
monodentate ligands
a ligand that forms one co-ordinate bond to the central metal ion (one lone pair to donate)
bidentate ligand
ligand that forms two co-ordinate bonds to the metal ion (2 lone pairs to donate)
multidentate ligand
a ligand that forms three or more co-ordinate bonds to the central metal ion
examples of common monodentate ligands
H2O, NH3, OH-
how many co-ordinate bonds does EDTA4- form?
6
coordination number
the number of co-ordinate bonds the metal ion has formed to surrounding ligands
chelate effect
chelate complexes with multidentate ligands are favoured over monodentate ligands or ligands that form fewer coordinate bonds per molecule
explain the chelate effect in terms of entropy and the reaction that is occurring
number of molecules increases when multidentate ligands displace ligands that form fewer co-ordinate bonds per molecule
significant increase in entropy –> Gibbs’ free energy change < 0 –> feasible reaction
a more stable complex ion is formed
what ion is usually formed when a transition metal compound is dissolved in water? what shape is it?
aqua ion
6 H2O ligands around the central metal ion
octahedral shape
if a transition metal has 2 ligands, what shape is it usually?
linear
if a transition metal has 4 ligands, what shape is it usually?
tetrahedral
exception to the general rule that ions with 4 ligands are tetrahedral? what shape is it?
platin
square planar – > forms cisplatin
what shape is a complex ion if it has 6 ligands?
octahedral
how can complex ions display E-Z or cis-trans isomerism? what shapes of ion does this apply to?
ligands differ in the way in which they are arranged in space
2 ligands of the same type can be on the same side of the metal ion (next to each other), which forms the Z or cis isomer
2 ligands of the same type can be on opposite sides of the metal ion (not next to each other), which forms the E or trans isomer
applies to square planar and octahedral complex ions
what conditions are needed for a complex ion to display optical isomerism?
usually applies to octahedral molecules with 2 or more bidentate ligands, so that the mirror images are non-superimposable
what happens to Co2+, Cu2+ and Fe3+ ‘s coordination numbers when Cl- ligands replace NH3 or H2O ligands?
decreases from 6 to 4 as Cl- is much larger than H2O and NH3
what is haem - its metal ion, coordination number and ligands?
a molecule which makes up protein chains with an Fe 2+ central metal ion, which has a coordination number of 6
4 of these bonds are to a ring system called porphyrin. 1 is to the nitrogen of a globin (protein) molecule and one is to an oxygen in an O2 molecule
how does haemoglobin transport oxygen?
O2 forms a weak coordinate bond to the metal ion, then is transported around the body
the bond breaks when haemoglobin reaches cells and oxygen is released
why is CO toxic with regards to the body biologically?
CO also coordinately bonds to the Fe2+, and is a better ligand, so bonds more strongly than O2
stops O2 from bonding to haemoglobin so O2 cannot be transported around the body
why are transition metal compounds coloured?
partially filled d-orbitals so electrons are able to move between the d-orbitals
in compounds (when ligands coordinately bond to the ion), the d-orbitals split into different energy levels
electrons can absorb energy in the form of photons to become excited and move to a higher energy level. energy of photon = energy difference between levels
energy of photon is related to frequency of light by E = hf
the colour corresponding to the frequency of the energy change is missing from the spectrum, so we see a combination of all the colours that aren’t absorbed
what affects the colour of a transition metal compound?
ΔE affects the frequency of absorbed photons, so determines the colour
ΔE is changed by oxidation state of the metal, number and type of ligands, shape, co-ordination number
why is there a lack of colour in some aqueous ions and other complex ions?
ions that have completely filled 3d energy levels (such as Zn2+) and ions that have no electrons in their 3d energy levels (such as Sc3+) are not coloured those that have partially filled 3d energy levels are coloured
what are the vanadium oxidation numbers and colours? VO2 +, VO2+, V3+, V2+
VO2^+, oxidation =5+, yellow
VO^2+, oxidation =4+, blue
V^3+, oxidation = 3+, green
V^2+, oxidation = 2+, violet
what can you use to reduce vanadium?
zinc
equation and observation of reduction of V3+ to V2+ using zinc
green to violet
V3+ + e- –> V2+
Zn2+ + 2e- –> Zn
as zinc has a more negative electrode potential than the vanadium half equation zinc will reduce down to V2+
2V3+ + Zn –> Zn2+ + V2+
what colour is Fe2+’s aqua ion?
green