23 transition metals Flashcards
how do you define a transition element?
an element that forms at least one stable ion with a partially filled d sub shell
why is scandium not a transition element?
only forms Sc3+ which makes a non-partially filled d sub shell (3d0)
give 4 features of a transition element
- forms complex ions
- coloured ions
- catalytic properties
- variable oxidative states
define a co-ordinate bond
a shared pair of electrons where both electrons come from the same atom
define a ligand
a lone pair of electrons which can form a co-ordinate bond with a transition metal ion
define coordination number
number of coordinate bonds formed
define complex ion
central atom/ion surrounded by ligand
what is a:
monodentate ligand?
bidentate ligand?
multidentate ligand?
monodentate- each ligand forms 1 coordinate bond
bidentate- each ligand forms 2 coordinate bonds
multidentate ligand- each ligand forms 2 or more coordinate bonds
what are 5 monodentate ligands?
:H2O
:NH3
:Cl
:OH-
:CN
what are 2 bidentate ligands?
1,2-diaminoethane
ethanedioate ion
what is the structural formula for 1,2-diaminoethane?
NH2CH2CH2NH2
what does an ethanedioate ion look like?
2 carbons
double bond O attached to each
single bond :O- attached to each
what are 4 common shapes transition metal complexes can form?
octahedral
linear
square planar
tetrahedral
how many bonds does each shape transition metal complexes can form have?
octahedral- 6
linear- 2
tetrahedral- 4
square planar- 4
give 2 examples of complexes that form octahedral shapes
[Cu(H2O)]2+
[Co(NH3)6]2+
give an example of a complex with a tetrahedral shape
[CoCl4]2-
why can’t transition metals with Cl ligand be octahedral?
because Cl ions are large and only 4 can fit around the transition metal
give an example of a complex with a square planar shape
[Ni(CN)4]2-
give the structural formula of the complex that forms an octahedral shape with multidentate ligands
[Ni(NH2CH2CH2NH2)3]2+
name a hexadentate ligand
EDTA4-
what shape does EDTA4- form in a complex?
octahedral
what is a ligand substitution reaction?
when a ligand attached to the transition metal ion is replaced by a different ligand
give the equation to show how the complex [CU(H2O)6]2+ can be turned into [CU(H2O)3(NH3)3]2+
[Cu(H2O)6]2+ + 3NH3 –> [Cu(H2O)3(NH3)3]2+ + 3H2O
give the equation to show how [Cu(H2O)6]2+ can be turned into [CuCl4]2-
[Cu(H2O)6]2+ + 4Cl- –> [CuCl4]2- + 6H2O
what is the chelate effect?
when a monodentate ligand is substituted by a bidentate ot multidentate ligand and a large increase of entropy occurs
why does a large increase of entropy occur when a monodentate ligand gets replaced by a bidentate or a multidentate ligand?
because there is an increase in molecules on the right hand side of the equation
define stereoisomer
same structural formula but different arrangement of atoms in space
what are the two types of stereoisomerism transition metals can display?
geometrical and optical
what is a cis isomer in an octahedral complex?
where alike ligands are arranged next to each other at a 90° angle
what is a trans isomer in an octahedral complex?
where alike ligands are arranged opposite from each other at a 180° angle
what is a cis isomer in a square planar complex?
if alike ligands are next to each other
what is a trans isomer in a square planar complex?
if alike ligands are apposite to one another
what is the structural formula for cisplatin?
[PtCl2(NH3)2]
what is cisplatin?
a very effective anti-caner drug when it is a cis isomer
how does cisplatin work?
binds to cancerous cells to stop cell replication
(Cl- on cisplatin are substituted for N on guanine)
what are the colours that make up white light?
red
orange
yellow
green
blue
indigo
violet
which colours in white light have lower energy?
red orange yellow
which colours in white light have higher energy?
blue indigo violet
why are most transition metal compounds coloured?
partially filled d sub shell absorbs some of the colours from white light and transmits other colours
what do the electrons in the d orbital need to be excited?
energy from white light
where are the d orbital electrons excited to and from?
ground state to excited state
how do you calculate the change in energy absorbed by electrons?
ΔE = hv
or
ΔE = h c/λ
what do the letters in ΔE = hv stand for?
ΔE - change in energy
h - Planck’s constant (J s)
v- frequency of light ( s-1)
what do the letters in ΔE = h c/λ stand for?
ΔE - change in energy
h - Planck’s constant (J s)
c - speed of light
λ - wavelength of light (m)
how many m is 1nm
1x10^-9
what does big e BIV abs mean?
- transition metal has large ΔE between d sub shells
- high energy light
- will be absorbed to excite electrons
- ROY will be transmitted to make compound look red
what does small e ROY abs mean?
- transition metal has a small ΔE between d sub shells
- low energy light
- will be absorbed to excite electrons
- BIV will be transmitted to make compound look blue
what changes could alter the colour of a compound?
- change in Ligands
- change in Oxidation states
- change in Coordination number
- change in Shape of complex
what apparatus can you use to measure the amount of light absorbed?
colorimeter
how does a colorimeter work?
- light source shines a light of specific frequency through solution
- some light absorbed some light transmitted
- transmitted light hits the detector
- detector gives reading for the amount of light which passed through
what does a 1.0 transmittance reading mean in colorimetry?
that all the light passed through the sample and none was absorbed
what can colorimetry also be used to determine?
an unknown concentration of a transition metal ion
how can colorimetry determine an unknown concentration of a transition metal ion?
- measure absorbance of known concentrations
- plot graph: absorbance against concentration
- read value of conc for measured absorbance from graph
what physical factor when doing a colorimetry test affects the amount of absorption?
length of container affects distance light has to travel
what does a filter do in colorimetry?
only lets one colour of light through sample
what does placing a cuvette filled with water into colorimeter and setting to zero do?
ensures accuracy and negates absorbance due to solvent
what is a catalyst?
a substance that increases the rate of reaction without being used up
how does a catalyst work?
by providing an alternative pathway with a lower activation energy
when a catalyst is added, which way does Ea move on a maxwell boltzmann distributon?
to the left
what is a heterogeneous and a homogeneous catalyst?
heterozygous- where the catalyst is in a different phase to the reactants
homozygous- where the catalyst is in the same phase as the reactants
what state is a heterogeneous catalyst usually in?
solid
list the steps of a heterogeneous catalyst
- reactants adsorb onto surface of catalyst on active site
- reaction occurs on surface of catalyst (bonds weaken)
- products desorb from the surface of catalyst
what does adsorb mean?
stick
what ate 3 heterogeneous catalyst examples?
- solid iron
making ammonia in the haber process - solid V2O5
making sulfuric acid - solid chromium (III)
manufacture of methanol
what is the equation that solid iron catalyses?
making ammonia in the haber process:
N2(g) + 3H2(g) ⇌ 2NH3(g)
what is the equation that solid V2O5 catalyses?
making sulfuric acid in the contact process
SO2(g) + V2O5(s) ⇌ SO3(g) + VsO4(s)
2V2O4(s) + O2(g) ⇌ 2V2O5
2SO2(g) + O2(g) -> 2SO3
sulfuric acid formed by reacting with water
what is the equation that solid chromium(III) catalyses?
manufacture of methanol
CO(g) + 2H2(g) -> CH3OH(g)
what state are the majority of homogeneous catalysts and reactants in?
aqueous
why can transition metals act as catalysts?
they have variable oxidation states
why can’t group 1 metals be catalysts?
they only exist in one oxidation state
give an example of a homogeneous catalyst
Fe2+
what is the equation that Fe2+ catalyses?
S2O8^2- + 2I- -> 2SO4^2- +2Fe3+
2I- + 2Fe3+ -> I2 +2Fe2+
(all states aqueous)
