Chemistry of transition elements

Question 1

Transition elements

Answer 1

d-block elements which form one or more stable ions with an incomplete d subshell

Question 2

The d-block elements which aren’t classed as transition metals

Answer 2

Scandium and Zinc

Question 3

Scandium is not classed as a transition element because

Answer 3

It only forms one ion, Sc3+, that has no electrons in its 3d subshell; it has the electronic configuration of [Ar]

Question 4

Zinc is not classed as a transition element because

Answer 4

It forms only one ion, Zn2+, that has a complete 3d subshell; it has the electronic configuration [Ar]3d10

Question 5

The five orbitals in a d subshell

Answer 5

3dyz
3dxz
3dxy
3dx2 - y2
3dz2

Question 6

Special properties of transitional elements

Answer 6

~Variable oxidation states
~Behave as catalysts
~Form complex ions
~Form coloured compounds

Question 7

The most common oxidation states of Titanium/TI

Answer 7

+3 and +4

Question 8

The most common oxidation states of Vanadium/V

Answer 8

+2, +3, +4 and +5

Question 9

The most common oxidation states of Chromium/Cr

Answer 9

+3 and +6

Question 10

The most common oxidation states of Manganese/Mn

Answer 10

+2, +4, +6 and +7

Question 11

The most common oxidation states of Iron/Fe

Answer 11

+2 and +3

Question 12

The most common oxidation state of Nickel/Ni

Answer 12

+2

Question 13

The most common oxidation states of Copper/Cu

Answer 13

+1 and +2

Question 14

Why do transitional metals make excellent catalysts

Answer 14

~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

Question 15

Why transitional elements can form ions with variable oxidation states

Answer 15

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

Question 16

When the transition elements form ions, the electrons of

Answer 16

the 4s subshell are lost first, followed by the 3d electrons

Question 17

The most common oxidation state is

Answer 17

+2, which is usually formed when the two 4s electrons are lost

Question 18

Transition elements can easily form complex ions because

Answer 18

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

Question 19

ligand

Answer 19

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

Question 20

Monodentate ligands

Answer 20

can form only one dative bond to the central metal ion

Question 21

Bidentate ligands

Answer 21

can each form two dative bonds to the central metal ion- this is because each ligand contains two atoms with lone pairs of electrons

Question 22

complex

Answer 22

a molecule or ion formed by a central metal atom or ion surrounded by one or more ligands

Question 23

complex ion

Answer 23

if a complex has an overall charge it is called a complex ion

Question 24

coordination number

Answer 24

the number of dative bonds formed between the central metal ion and the ligands

Question 25

Shapes of complexes with a coordination number of 6

Answer 25

octahedral

Question 26

Shapes of complexes with a coordination number of 4

Answer 26

tetrahedral or square planar

Question 27

bond angles in linear complexes are

Answer 27

180 degrees

Question 28

bond angles in tetrahedral complexes are

Answer 28

109.5 degrees

Question 29

bond angles in square planar complexes are

Answer 29

90 degrees

Question 30

bond angles in octahedral complexes are

Answer 30

90 degrees

Question 31

isolated transition element

Answer 31

an atom or ion that is not bonded to anything else

Question 32

degenerate orbitals

Answer 32

orbitals are all at the same energy level (they are equal in energy)

Question 33

The five d orbitals in an isolated transition element are

Answer 33

degenerate orbitals

Question 34

The dative bonding from the ligands causes

Answer 34

the five d orbitals to split into two sets of non-degenerate orbitals

Question 35

non-degenerate orbitals

Answer 35

orbitals that are not equal in energy

Question 36

Splitting of orbitals in octahedral complexes

Answer 36

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

Question 37

ΔE

Answer 37

The difference in energy between the non-degenerate d orbitals

Question 38

Splitting of orbitals in tetrahedral complexes

Answer 38

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

Question 39

Why are transition element complex solutions coloured

Answer 39

they absorb part of the electromagnetic spectrum in the visible light region

Question 40

The observed colour in coloured solutions

Answer 40

is the complementary colour which is made up of light with frequencies that are not absorbed

Question 41

copper(II) ions absorb light from the red end of the spectrum so the complementary colour observed is therefore

Answer 41

pale blue (cyan)

Question 42

When light shines on a solution containing a transition element complex

Answer 42

an electron will absorb the frequency of light which corresponds to the exact amount of energy (ΔE) between their non-degenerate d orbitals

Question 43

amount of energy absorbed by an electron in a complex can be worked out by the equation

Answer 43

ΔE = h x v

Question 44

h =

Answer 44

Planck's constant (6.626 x 10-34 m2 kg s-1)

Question 45

v =

Answer 45

frequency (Hertz, Hz or s-1)

Question 46

The electron uses the energy from the light to

Answer 46

jump into a higher, non-degenerate energy level- electro promotion

Question 47

The other frequencies of light which are not absorbed combine to make the

Answer 47

complimentary colour

Question 48

ΔE is affected by

Answer 48

the different ligands which surround the transition element ion

Question 49

What causes the size of ΔE and thus the frequency of light absorbed by the electrons to be slightly different?

Answer 49

Different ligands split the d orbital by a different amount of energy depending on the repulsion that the d orbital experiences from these ligands

Question 50

depending on the size of ΔE

Answer 50

a different colour of light is absorbed by the complex solution and a different complementary colour is observed

Question 51

complexes with similar transition elements ions, but different ligands, can have

Answer 51

different colours

Question 52

colour of [Cu(H2O)6]2+ solution

Answer 52

light blue

Question 53

colour of [Cu(NH3)4(H2O)2)]2+ solution

Answer 53

deep blue

Question 54

colour of [Co(H2O)6]2+ solution

Answer 54

pink

Question 55

colour of [Co(NH3)6]2+ solution

Answer 55

brown

Question 56

Ligand exchange

Answer 56

when one ligand in a complex is replaced by another

Question 57

Ligand exchange forms

Answer 57

a new complex that is more stable than the original one

Question 58

During ligand exchange, if the ligands are of a similar size

Answer 58

there are no changes in the coordination number or the geometry of the complex

Question 59

During ligand exchange, if the ligands are of a different size

Answer 59

then a change in coordination number and the geometry of the complex will occur

Question 60

When a transition element ion is in solution, it can be assumed that it exists as a

Answer 60

hexaaqua complex ion (i.e. it has six water ligands attached to it)

Question 61

[Cu(H2O)6]2+ (aq) complex ion colour

Answer 61

blue

Question 62

What happens upon dropwise addition of sodium hydroxide (NaOH) solution to [Cu(H2O)6]2+ (aq)

Answer 62

[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

Question 63

What happens upon the addition of excess concentrated ammonia (NH3) solution to Cu(OH)2(H2O)4(s)

Answer 63

Cu(OH)2(H2O)4(s) +