unit 1a: transition metals Flashcards
transition metals
metals with an incomplete d-subshell in at least one of their ions
variable valency
transition metals can form ions with different charges by losing different numbers of electrons
scandium and zinc
these are not transition metals as there is not an incomplete d-subshell in the ions they form
properties
form coloured ions, form complexes, variable oxidation states, show catalytic activity
oxidation state
an element is said to be in a particular oxidation state when it has a specific oxidation number, related to the number of electrons the species has lost or gained
oxidation number in a free element
0 e.g. Mg=0 and Cl2=0
for monatomic ions, the oxidation number is
equal to the charge, e.g. Cl^-1=-1 and Al^3+=+3
oxidation number for oxygen
-2
oxidation number for hydrogen
+1
group 1 metals and group 2 metals
+1 and +2
oxidation number in compounds
fluorine, the CN^-1 ion, and all of group 7 is always equal to -1
in molecule the sum of all oxidation numbers is
equal to 0, e.g. H20=0
in a polyatomic ion, the sum of the oxidation numbers is
equal to the charge of the ion, e.g. SO4^2-=-2
oxidation involves
increase in oxidation number
reduction involves
decrease in oxidation number
metals high in oxidation states tend to be good
oxidising agents
what two elements in the box are not transition metals
scandium and zinc
redox acronym
OILRIG
ligand definition
electron donors, may be negative ions or molecules with non-bonding pairs of electrons
a complex consists of
a central metal ion surrounded by ligands
dative bond
when both electrons of the shared pair come from the same atom
ligands have at least
one lone pair of electrons
monodentate
when a ligand uses just one atom to bind to the central metal
bidentate
when a ligand uses two atoms to bind to the central metal
example of a hexadentate ligand
ethylenediaminetetraacetate- EDTA
monodentate ligands- negative ions
fluoride F- , chloride Cl- , cyanide CN-
monodentate ligands- neutral molecules
water H2O , ammonia NH3
bidentate ligand- negative ion
oxalate C2O4^2-
coordination number
the total number of bonds from the ligands to the central transition metal atom/ion
if the complex ion is negative the transition metal name will end in
-ate
if the ligand is a negative ion the name in complex will
replace the “e” ending with “o” e.g. bromine —> bromido
CO name in complex ion
carbonyl
H2O name in complex ion
aqua
NH3 name in complex ion
ammine
Fe name in complex ion
ferrate
Cu name in complex ion
cuprate
coordination compound
when a complex ion combines with oppositely charged ions
if the complex is a positive ion it will appear
first in the formula and the name
if the complex is a negative ion
it will appear last in the formula and the name
three primary colours of visible light
red , green , and blue
complementary colour
transmitted light from certain chemicals(when white light shines on certain chemicals they may absorb some of the. visible light, the colour we see is the white light minus absorbed light)
when red light is absorbed
blue and green are transmitted and cyan is observed
when blue light is absorbed
red and green are transmitted and yellow is observed
when green light is absorbed
red and blue are transmitted and magenta is observed
a more concentrated soloution will absorb more
light than a dilute solution and be darker in colour
extent of d orbital splitting factors
the metal involved , the oxidation state of the metal , the nature of the ligand
spectra chemical series
CN-, NH3, H2O, OH-, F-, Cl-, Br-, I-
start of the spectrochemical series
weaker field , smaller delta , longer wavelength
end of the spectrochemical series
stronger field , larger delta , shorter wavelength
weakest at splitting d orbitals
I-
strongest at splitting d orbitals
CO
crystal field theory
explains how transition metals (with an incomplete 3d subshell) are coloured, only applies to octahedral complexes
splitting
as a result of ligands approaching and bonding to the metal, the five 3d orbitals are no longer degenerate
delta
the splitting energy
d to d transition
when any of the three lower d orbitals absorb energy and are promoted to one of the two higher energy d orbitals
how the metals transmit the colours
if the energy absorbed is equal to a wavelength of light in the visible spectrum, the compound will transmit its complementary colour
catalyst of the haber process
iron
catalyst of the contact process
vanadium (V) oxide
catalyst of the ostwald process
platinum
catalyst for catalytic converters in cars
platinum , palladium , rhodoum
catalyst for the production of methanol
copper
catalyst for the hardening of oils to fats
nickel
catalyst for the polymerisation of alkenes
titanium compounds
how catalysts speed up chemical reactions
by providing an alternative reaction pathway of lower activation energy
why do many transition metals act as catalysts
due to their ability to exist in a variety of different oxidation states
how do ligands form complexes with metal atoms
donate pairs of electrons
homogeneous
same state as reactants, change their oxidation allowing formation of intermediate complexes, then reverts back to its original state
heterogeneous
different state as reactants, work by absorption of the reactant molecules to their active sites, presence of unpaired d-electron allow activated complex to form providing an alternative pathway and activation energy
how do transition metals act as catalysts
unpaired d electrons (donating and accepting electrons)
how do unpaired electrons arise in H20 easier than in CN-
H2O has a smaller splitting energy so it is easier for electrons to jump up to the higher energy d orbitals
why are transition metals coloured
light is absorbed when electrons in lower energy d orbitals are promoted in a d-d transition, if the energy absorbed is visible light then it will be coloured
changing the ligand in a complex can
change the colour
a complex may be colourless because
it was in the UV spectrum, it has a full d subshell
what causes d orbital splitting
lone pairs of electrons in the ligand
