24 - Transition elements Flashcards
what are d-block elements?
properties
- 3d sub-shell has the highest energfy and electrons are added to 3d orbitals
- metallic, high MP and BP, shiny, conduct electricity and heat
how are d-block orbitals filled
how are ions formed
atoms of d-block elements fill their 4s sub shell before the 3d sub shell
- 4s sub shell is at a lower energy than 3d
-> ions formed by emptying the 4s orbital before the 3d
what are the exceptions to the expected filling of block elements
chromium and copper
In both cases an electron is promoted from the 4s to the 3d to achieve a half full and full d-subshell, respectively
Chromium and copper have the following electron configurations, which are different to what you may expect:
Cr is [Ar] 3d5 4s1 not [Ar] 3d4 4s2
Cu is [Ar] 3d10 4s1 not [Ar] 3d9 4s2
This is because the [Ar] 3d5 4s1 and [Ar] 3d10 4s1 configurations are energetically more stable
what are transition metals
d-block elements that form at least one ion with a partially filled d-orbital
- Sc and Zn dont fit this definition
Scandium only forms the ion Sc3+, configuration [Ar] 3d0
Zinc only forms the ion Zn2+, configuration [Ar] 3d10
General properties of TM
Variable oxidation states
Form complex ions
Form coloured compounds
Behave as catalysts
Variable Oxidation States?
- can form compounds withmore than one oxidation state
-> Iron(II) FeCl2 and Irons(III) FeCl3
-the number of oxidation states increase across the period to manganese, then decreases
Forming coloured compounds
- compounds and ions of TM are often coloured
->colour of the solution of a TM compound depends on the oxidation state
Iron and it coloured compounds
Iron II -> pale green
Iron II -> yellow
Chromium and its coloured compounds
Cr III -> green
Cr VI -> yellow or orange
Transition elements as catalysts
Since transition elements can have variable oxidation states, they make excellent catalysts
During catalysis, the transition element can change to various oxidation states by gaining electrons or donating electrons from reagents within the reaction
Substances can also be adsorbed onto their surface and activated in the process
give 2 examples of TM as catalysts
An example is the use of iron, Fe, in the Haber process for making ammonia
N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
The decomposition of hydrogen peroxide is a common reaction in the study of chemical kinetics and uses manganese(IV) oxide as the catalyst
2H2O2 (g) → 2H2O (aq) + O2 (g)
complex ion
is formed when one or more molecules or negatively charged ions bond to a central metal ion
what is a ligand?
- a molecule of ion that donates a pair of electrons to a central metal ion to form a coordinate bond/dative covalent bond
what is dative/coordinate bond?
- when one of the bonded atom provides both of the electrons for the bond
what is the coordination number?
the number of coordinate bonds attached to the central metal ion
monodentate ligands
give examples
a ligand that can donate one pair of electrons to a central metal ion
H20:
:NH3
:Cl-
:CN-
:OH-
Bidentate ligands
give examples
can donate two lone pairs of electrons to the central metal ion - each molecule can form two coordinate bonds
1,2 - diaminoethane or en
ethanediote (oxalate) ion
where are the lone pairs on 1,2 - diaminoethane and ethanediote (oxalate) ion
- each nitrogen atom donates a pair of electrons
- each negatively charged oxygen atom donates a lone pair
shape of a complex ion with six coordinate bonds?
it gives an octahedral shape
- bond angle is 90
shape of a complex ion with 4 coordinate bonds?
tetrahedral
-> 109.5
square planar
-> 90
when is a complex ion tetrahedral or square planar?
- square planar when there are 8 electrons d-electrons in the highest energy d-sub-shell
-Platinum II
palladium II
gold III
what kind of stereoisomerism do complex ions show
cis-trans isomerism
optical
when can a complex ion show cis-trans isomerism?
four coordinate square planar complexes that have no more then two identical ligands
six coordinate complex ions monodentate (four of one type of one ligand and two of of another type of ligand)
four and six coordinate complex ions containing two different monodentate ligands
what kind of stereoisomerism does this show
cis-trans
some six coordinate complex ions with monodentate and bidentate ligands
what kind of stereoisomerism does this show
cis-trans and optical
when does a complex ion show optical isomerism
some six coordinate complex ions with monodentate and bidentate ligands
explain cis-trans isomerism in square planar complexes
- found in four coordinate square planar complexes that have no more than two identical ligands
- the ligands are arranged in the same plane at the corners of a square of a square at 90
- cis isomer has two identical groups adjacent to each other 90 degrees to each other
- trans isomer has two identical ligands opposite to each other (hypotenuses). 180 degrees between each other
give an example of cis-trans isomerism in a square planar complex
-> draw it boyyyyyy
[Pd(NH3)2CL2]
explain cis-trans isomerism in octahedral complex with monodentate ligands
let the ligands be 4 x A and 2 x B
Cis-> two B ligands aare adjacent to each other at 90 degrees
Trans -> two B ligands are at 180 degrees to each other and on the same plane
give an example of cis-trans isomerism in octahedral complex with monodentate ligands
draw it lazy bitch
[Co(NH3)4Cl2]+
explain cis-trans isomerism in octahedral complex with bidentate ligands
structural formula of en
NH2CH2CH2NH2
explain optical isomerism in octahedral complexes
- optical isomerism only occurs in octahedral complexes containing two or more bidentate ligands
- enantiomers are non-superimposable mirror images of each other
- the cis isomer of a octahedral complex with 2 x B(bidentate) can exist as two optical isomers but the trans isomer cant- it can be superimposed
colours of chromium ions
Cr2O7 2- (Cr= +6) is orange
Cr3+ (Cr=+3) is green
Cr 3+ metal aqua ion
violet solution
[Cr(H2O)6]3+
Fe 3+ metal aqua ion
yellow solution
[Fe(H2O)6]3+
Fe 2+ metal aqua ion
pale green solution
[Fe(H2O)6]2+
Mn 2+ metal aqua ion
Pale pink
[Mn(H2O)6]2+
Cu 2+ metal aqua ion
pale blue
[Cu(H2O)6]2+
Cr 3+ with little OH-
Grey?
[Cr(OH)3(H2O)3] (s)
Cr 3+ with excess OH-
dark green solution
[Cr(OH)6]3–
Cr 3+ with little NH3
green grey precipitate
[Cr(OH)3(H2O)3] (s)
Cr 3+ with excess NH3
Purple solution
[Cr(NH3)6]3+
Fe 3+ with little OH-
orange brown precipitate
Fe(OH)3(H2O)3(s)
Fe 3+ with excess OH-
orange brown precipitate
Fe(OH)3(H2O)3(s)
Fe 3+ with little NH3
Orange brown precipitate
Fe(OH)3(H2O)(s)
Fe 3+ with excess NH3
orange brown precipitate
Fe(OH)3(H2O)(s)
Cu 2+ with little OH-
Pale blue precipitate
Cu(OH)2(H2O)4(s)
OH- accept H+ from 2 water ligands
Cu 2+ with excess OH-
Pale Blue precipitate
Cu(OH)2(H2O)4(s)
OH- accept H+ from 2 water ligands
Cu 2+ with little NH3
Pale blue precipitate
Ammonia acts as a base
Cu(OH)2(H2O)4(s) + 2NH4+
Cu 2+ with excess NH3
deep blue solution
[Cu(NH3)4(H2O)2]2+
Cu 2+ with NH3 not in excess
deep blue solution
Mn 2+ with little OH-
light brown precipitate
Mn(OH)2(H2O)4(s)
Mn 2+ with excess OH-
light brown precipitate
Mn(OH)2(H2O)4(s)
Mn 2+ with little NH3
light brown precipitate
Mn(OH)2(H2O)4(s)
Mn 2+ with excess NH3
light brown precipitate
Mn(OH)2(H2O)4(s)
Fe 2+ with little OH-
Dark green precipitate
Fe(OH)2(H2O)(s)
Fe 2+ with excess OH-
Dqrk green precipitate
Fe(OH)2(H2O)(s)
Fe 2+ with little NH3
green precipitate
Fe(OH)2(H2O)(s)
Fe 2+ with excess NH3
green precipitate
Fe(OH)2(H2O)(s)
Iron Redos reactions, TM
Fe2+ + [O] -> Fe3+
- can be oxidised using MnO4- in acidic conditions
pale green -> orange brown
Chromium Redox reactions TM
oxidation states and compoiunds
Cr3+ Cr2O72- Cr2+
Chromium Redox reactions TM
reducing Cr2O7 2-
forms Cr3+ and Cr2+
using zinc in acidic conditions
Chromium Redox reactions TM
oxidising Cr3+
forms Cr2O7 2-
Using hydrogen peroxide in alkaline conditions
- initially forms CrO4 2- but converted to Cr2O7 2- by acidification
oxidation of Cr3+ with hot alkaline H2O2
CrO4 2-
yellow
Cr2O7 2-
from K2Cr2O7(s) in
0.1mol dm-3 H2SO4
orange
Copper Redox reactions TM
Cu2+ can be reduced by zinc
Cu+ to Cu and Cu2+
Disproportionation of Cu+
=brown solid (Cu) and
=blue solution (CuSO4
CuCl4 2-
excess HCl to Cu2+(aq)
yellow
CoCl4 2–
from CoCl2.6H2O(s) plus
water and excess HCl
blue
