Chapter 24 - Transition Elements

Question 1

What are the two irregularities in the d-block in terms of electron configuration?

Answer 1

Chromium: 3d5 4s1 instead of 3d4 4s2
Copper: 3d10 4s1 instead of 3d9 4s2

Anomaly due to stability of half or full subshell

Question 2

Why do these irregularities exist in the d block electron configurations?

Answer 2

A half filled and a fully filled d sub shell gives greater stability to these atoms.

Question 3

What are transition elements?

Answer 3

A transition metal is one they forms one or more stable ions which have incompletely filled d orbitals

Question 4

Which d-block elements are excluded from being transition elements?

Answer 4

Scandium and zinc

Question 5

What are the properties of the transition elements?

Answer 5

• Form compounds in which the transition element has different oxidation states (eg Mn has 7 due to electronic configuration being 3d5 4s2,
• Form coloured compounds
• Elements and compounds can act as catalysts

Question 6

What colour is potassium dichromate(VI)?

Answer 6

Orange

Question 7

What is the catalyst used in the Haber process?

Answer 7

Iron

Question 8

What is the catalyst used in the Contact process?

Answer 8

Vanadium(V) oxide

V2O5

Question 9

What is the catalyst used in hydrogenation?

Answer 9

Nickel

Question 10

What is the catalyst used in catalytic decomposition of hydrogen peroxide?

Answer 10

Manganese(IV) oxide

MnO2

Question 11

Define what a complex ion is

Answer 11

A transition metal ion bonded to ligands by coordinate bonds.

Question 12

Define coordination number

Answer 12

The number of coordinate bonds attached to the central metal ion.

Question 13

Define what a ligand is

Answer 13

A molecule or ion that can donate a pair of electrons from outer energy level to the transition metal ion to form a coordinate bond.

Question 14

What is meant by a monodentate ligand?

What’s bidente

Answer 14

A ligand that is able to donate one lone pair of electrons to a central metal ion.

(Any other lone pairs are pointing in wrong direction)

• has two lone pairs available in correct direction.

Question 15

Give 6 examples of common monodentate ligands and their charges

Answer 15

Water H2O neutral
Ammonia NH3 neutral
Thiocyanate SCN- -1
Cyanide CN- -1
Chloride Cl- -1
Hydroxide OH- -1

Question 16

What shape is created from a complex ion having a coordination number of 6?

Answer 16

Octahedral

Question 17

What shapes can be created from a complex ion having a coordination number of 4?

Answer 17

Tetrahedral
OR
Square planar

Question 18

When is a square planar shape formed in a complex ion?

Answer 18

When the transition metal in the complex ion has platinum, palladium and gold (8 d-electrons in highest energy d-orbital)

Question 19

What is stereoisomerism?

Answer 19

Same structural formula but a different arrangement in space.

Question 20

What are the two types of stereoisomerism?

Answer 20

Cis-trans isomerism

Optical isomerism

Question 21

When can complex ions show cis-trans isomerism?

Answer 21

Four or six coordinate complex ions with two different monodentate ligands.

Question 22

When can complex ions show both types of stereoisomerism?

Answer 22

Octahedral complexes w 6 coordinate bonds and two or more bidente ligand

Question 23

What is optical isomerism?

Answer 23

Non-superimposable mirror images of each other.

-One will rotate plane polarise light in one direction and one in the other direction

Trans = not optical as superimosable
Cis = optical because non superimposable

Question 24

Define ligand substitution

Answer 24

One ligand in a complex ion is replaced by another ligand.

Question 25

Describe ligand substitution of aqueous copper(II) ions with ammonia (ligand sub)

Answer 25

- Partial ligand sub w excess aq NH3 - pale blue to dark blue solution (Cu(h20)6)2+ + 4NH3 = (cu(nh3)4(h20)2+ + 4H2O

Question 26

Describe ligand substitution of aqueous copper(II) ions with chloride ions (ligand sub)

Answer 26

- Conc HCl used as source of chloride ions. - pale blue to yellow solution (Cu(h20)6)2+ + 4Cl- (equilibrium) (cucl4)2- + 6H2O

Question 27

Why does the solution of aqueous copper (II) ions reacting with chloride ions turn green as the reaction proceeds? (ligand sub)

Answer 27

The yellow and blue solutions mixing gives a green colour.

Question 28

Why does the shape of the aqueous copper (II) ion change from octahedral to tetrahedral when it reacts with chloride ions? (ligand sub)

Answer 28

Chloride ligands are larger in size than water ligands so fewer of them can fit around the Cu2+ ion.

Question 29

What is formed when chromium(III) ions react with ammonia (ligand sub)

Answer 29

- [Cr(H2O)6]3+ + 6NH3 = [Cr(NH3)6]3+ + 6H2O - initially Cr(OH)3 forms whixh is grey-green precip - the precip dissolves in excess NH3 to form complex ion [Cr(NH3)6]3+ - violet to purple

Question 30

What is formed instead when only chromium(III) sulphate is dissolved in water?

Answer 30

The complex ion [Cr(H2O)5SO4]+ is formed. | A green solution.

Question 31

How does ligand substitution help with gas exchange in blood?

Answer 31

In haemoglobins there is a central Fe2+ ion that can bind to oxygen gas. The oxygen is released to cells and carbon dioxide can bond to the Fe2+ where it is released in the lungs. Carbon monoxide binds to same site that oxygen would but forms very stable complex and doesn’t break away.

Question 32

What is a precipitation reaction?

Answer 32

Two aqueous solutions containg ions react together to form an insoluble ionic solid.

Question 33

Describe the precipitation reaction of Cu2+ with NaOH

Answer 33

Blue solution reacts to form a blue precipitation Cu2+ + 2OH- = Cu(OH)2

Question 34

How do Fe2+, Fe3+ and Mn2+ react with an excess of aqueous ammonia?

Answer 34

Same way as they react with NaOH. Form hydroxide precipitates. Insoluble in excess ammonia.

Question 35

What happens to 4s orbital of transition metals?

Answer 35

4s fills first but also looses first when forming an ion

Question 35

In terms of electron structures of their ions, whys it easier to oxidise fe(II) to Fe (III)

Answer 35

D6 to D5 = half full sub shell =increased stability.

Question 35

Why does number of possible oxidation numbers start to decrease after Mn?

Answer 35

Increasing positive charge from increasing nucleus size and decreasing atomic radius ( more energy to remove electrons)

Question 35

What bonding is between ligand and transition metal

Answer 35

Dative covalent bonding

Question 35

How do transition metals form compex ions??

Answer 35

To get six empty orbitals to accept the dative covalent bonds, the 4s, 4p and 4d orbitals are hybridised

Question 35

If ligands are small..

Answer 35

6 can fit at round the central metal ion whereas if they’re bigger then less can eg cl- can only fit 4( thus forming tetrahedral structure and coordination number of 4)

Question 36

The size of metal atom also plays a part in how many ligands can fit on the metal atom

Answer 36

Eg al+ and cu+ are tiny and thus can form less co-ordinate bonds and tend therefore to form linear structures.

Question 37

What atoms form square planar structures

Answer 37

Ni, Pt, palladium (II) and gold (III) It has restrictive rotation and can form stereoisomers

Question 38

Cus isomer degree Trans isomer degree

Answer 38

90° 180°

Question 39

Fe2+ with NaOh colour change (precip reactions)

Answer 39

Pale green soloution to green precip Green precip turns to brown at surface for standing in air (oxidised to Fe(III)

Question 40

Fe3+ with NaOh (precip reactions)

Answer 40

Pale yellow sol to orandge brown precip

Question 41

Mn2+ +NaOH colour change (precip reactions)

Answer 41

Pale pink to light brown

Question 42

Precip reaction with Cr3+ and NaOH

Answer 42

Forms Cr(OH)3 Violet to grey-green precip which is soluble in excess NaOH forming dark green sol [Cr(OH)6]3-

Question 43

Precipitation reaction with copper and chromium

Answer 43

For copper = Cu2+ + 2OH- = cu(OH)2 (blue precip) blue precip dissolves in excess ammonia to form deep blue soloution [cu(NH3)4(H2O)2]2+ For chromium = Cr3+ + 3OH- = Cr(OH)3 (grey green precip) Precip dissolves in excess NH3 to form [Cr(NH3)6]3+ (purple solution)

Question 44

Potassium dichromate colour

Answer 44

Bright orange

Question 45

Colbalt (II) chloride colour

Answer 45

Pink-purple