Chemistry of transition elements Flashcards
Transition elements
d-block elements which form one or more stable ions with an incomplete d subshell
The d-block elements which aren’t classed as transition metals
Scandium and Zinc
Scandium is not classed as a transition element because
It only forms one ion, Sc3+, that has no electrons in its 3d subshell; it has the electronic configuration of [Ar]
Zinc is not classed as a transition element because
It forms only one ion, Zn2+, that has a complete 3d subshell; it has the electronic configuration [Ar]3d10
The five orbitals in a d subshell
3dyz
3dxz
3dxy
3dx2 - y2
3dz2
Special properties of transitional elements
~Variable oxidation states
~Behave as catalysts
~Form complex ions
~Form coloured compounds
The most common oxidation states of Titanium/TI
+3 and +4
The most common oxidation states of Vanadium/V
+2, +3, +4 and +5
The most common oxidation states of Chromium/Cr
+3 and +6
The most common oxidation states of Manganese/Mn
+2, +4, +6 and +7
The most common oxidation states of Iron/Fe
+2 and +3
The most common oxidation state of Nickel/Ni
+2
The most common oxidation states of Copper/Cu
+1 and +2
Why do transitional metals make excellent catalysts
~because of their variable oxidation states: 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
Why transitional elements can form ions with variable oxidation states
variable oxidation states can be formed as the 3d and 4s atomic orbitals are similar in energy - this means that a similar amount of energy is needed to remove a different number of electrons
When the transition elements form ions, the electrons of
the 4s subshell are lost first, followed by the 3d electrons
The most common oxidation state is
+2, which is usually formed when the two 4s electrons are lost
Transition elements can easily form complex ions because
they have empty d orbitals that are energetically accessible- the empty d orbitals are therefore not too high in energy and can accommodate a lone pair of electrons
ligand
a molecule or ion (species) that has one or more lone pairs of electrons. These lone pairs of electrons are donated by the ligand, to form dative covalent bonds to a central metal atom or ion
Monodentate ligands
can form only one dative bond to the central metal ion
Bidentate ligands
can each form two dative bonds to the central metal ion- this is because each ligand contains two atoms with lone pairs of electrons
complex
a molecule or ion formed by a central metal atom or ion surrounded by one or more ligands
complex ion
if a complex has an overall charge it is called a complex ion
coordination number
the number of dative bonds formed between the central metal ion and the ligands
Shapes of complexes with a coordination number of 6
octahedral
Shapes of complexes with a coordination number of 4
tetrahedral or square planar
bond angles in linear complexes are
180 degrees
bond angles in tetrahedral complexes are
109.5 degrees
bond angles in square planar complexes are
90 degrees
bond angles in octahedral complexes are
90 degrees
isolated transition element
an atom or ion that is not bonded to anything else
degenerate orbitals
orbitals are all at the same energy level (they are equal in energy)
The five d orbitals in an isolated transition element are
degenerate orbitals
The dative bonding from the ligands causes
the five d orbitals to split into two sets of non-degenerate orbitals
non-degenerate orbitals
orbitals that are not equal in energy
Splitting of orbitals in octahedral complexes
1)The lone pairs of electrons of the six ligands repel the electrons in the x2-y2 and z2 orbitals of the metal ion more than they repel the electrons in the 3dyz, 3dxz, and 3dxy orbitals
2) This is because the ligands are attached to or approaching the central metal ion along the x, y and z axes, and the 3dx2-y2 and 3dz2 orbitals have lobes along these axes, thus the 3dx2-y2 and 3dz2 orbitals line up with the dative bonds in the complex’s octahedral shape
3)The electrons in these two orbitals are closer to the bonding electrons, so there is more repulsion
4)This means that when the d orbitals split, the 3dx2-y2 and 3dz2 orbitals are at a slightly higher energy level than the other three
ΔE
The difference in energy between the non-degenerate d orbitals
Splitting of orbitals in tetrahedral complexes
1)The bonding pair of electrons from the four ligands now line up with the 3dyz, 3dxz, and 3dxy orbitals of the central metal ion
2)Now, the 3dx2-y2 and 3dz2 orbitals lie between the metal-ligand bonds
3)Therefore, there is less repulsion with the 3dx2-y2 and 3dz2 orbitals
4)When the d orbitals split this time, the 3dx2-y2 and 3dz2 orbitals are at lower and more stable energy level than the other three
Why are transition element complex solutions coloured
they absorb part of the electromagnetic spectrum in the visible light region
The observed colour in coloured solutions
is the complementary colour which is made up of light with frequencies that are not absorbed
copper(II) ions absorb light from the red end of the spectrum so the complementary colour observed is therefore
pale blue (cyan)
When light shines on a solution containing a transition element complex
an electron will absorb the frequency of light which corresponds to the exact amount of energy (ΔE) between their non-degenerate d orbitals
amount of energy absorbed by an electron in a complex can be worked out by the equation
ΔE = h x v
h =
Planck’s constant (6.626 x 10-34 m2 kg s-1)
v =
frequency (Hertz, Hz or s-1)
The electron uses the energy from the light to
jump into a higher, non-degenerate energy level- electro promotion
The other frequencies of light which are not absorbed combine to make the
complimentary colour
ΔE is affected by
the different ligands which surround the transition element ion
What causes the size of ΔE and thus the frequency of light absorbed by the electrons to be slightly different?
Different ligands split the d orbital by a different amount of energy depending on the repulsion that the d orbital experiences from these ligands
depending on the size of ΔE
a different colour of light is absorbed by the complex solution and a different complementary colour is observed
complexes with similar transition elements ions, but different ligands, can have
different colours
colour of [Cu(H2O)6]2+ solution
light blue
colour of [Cu(NH3)4(H2O)2)]2+ solution
deep blue
colour of [Co(H2O)6]2+ solution
pink
colour of [Co(NH3)6]2+ solution
brown
Ligand exchange
when one ligand in a complex is replaced by another
Ligand exchange forms
a new complex that is more stable than the original one
During ligand exchange, if the ligands are of a similar size
there are no changes in the coordination number or the geometry of the complex
During ligand exchange, if the ligands are of a different size
then a change in coordination number and the geometry of the complex will occur
When a transition element ion is in solution, it can be assumed that it exists as a
hexaaqua complex ion (i.e. it has six water ligands attached to it)
[Cu(H2O)6]2+ (aq) complex ion colour
blue
What happens upon dropwise addition of sodium hydroxide (NaOH) solution to [Cu(H2O)6]2+ (aq)
[Cu(H2O)6]2+(aq) + 2OH-(aq) → Cu(OH)2(H2O)4(s) + 2H2O(l)
-a light blue precipitate is formed
-partial ligand substitution of two water ligands by two hydroxide ligands has occurred
What happens upon the addition of excess concentrated ammonia (NH3) solution to Cu(OH)2(H2O)4(s)
Cu(OH)2(H2O)4(s) +
