13.1 Coloured complexes

Question 1

list out the key properties of the transition metals

Answer 1

• a high melting point, boiling point and density
• act as catalysts in reactions
• exhibits temporary magnetism in response to external magnetic fields
• they all have +2 oxidation states
• all form coloured complexes
• all form complex ions

Question 2

define paramagnetism

Answer 2

strong and results from alignment of unpaired electrons
- paramagnetic atoms are attracted to a magnet

Question 3

define diamagnetic

Answer 3

weak and results from alignment of paired electrons
- diamagnetic atoms are repelled by magnets

Question 4

what are complex ions?

Answer 4

structures composed of a transition metal ion surrounded by ligands
held in place by dative covalent bonds

Question 5

define dative covalent bonds

Answer 5

form of covalent bond where both electrons are donated by a single atom

Question 6

define ligand

Answer 6

species with a spare pair of electrons, known as a lone pair, that forms dative covalent bonds with a central ion

Question 7

what are the 2 types of ligands?

Answer 7

1. monodentate; one lone pair, e.g. h2o and nh3
2. polydentate; more than one lone pair, e.g. nh2ch2ch2nh2

Question 8

what’s a coordination number?

Answer 8

number of lone pairs bonded to the transition metal ion

Question 9

what are the oxidation states for water and ammonium ligands?

Answer 9

neutral, 0

Question 10

what are the oxidation states for halides, hydroxides and cyanide ligands?

Answer 10

-1

Question 11

how does coloured complexes form?

Answer 11

when a transition metal is surrounded by ligands in a complex ion, there is a repulsion between the d-orbital electrons and the ligands lone pair

Question 12

why are transition metals coloured?

Answer 12

• d-d orbitals splits
• partially filled d subshells (d1 - d9)

Question 13

explain the d-d transition phenomenon where complex ions absorbs light

Answer 13

• visible light promotes an electron from a lower energy d-orbital to a higher energy d-orbital
• complex ions appears complementary in colour to the light that is absorbed

Question 14

what are the 2 main factors that affect the colour of the complex ion

Answer 14

• identity of the metal
• nature of the ligand

Question 15

what does it mean if the nature of ligands is further to the right or further to the left? (series can be found in section 15)

Answer 15

further to the right: the bigger the split for the ligands
further to the left: the smaller/ lower the split

Question 16

what does more splitting mean in terms of light frequency?

Answer 16

the more splitting there are, the higher frequency of light that is absorbed

Question 17

whats the colour of [Cu(H2O)6]^2+?

Answer 17

blue

Question 18

whats the colour of [Cu(NH3)4(H2O)2]^2+?

Answer 18

deep blue

Question 19

whats the colour of [Fe(SCN)(H2O)5]^2+?

Answer 19

blood red

Question 20

what is the colour of [Ni(H2O)6]^2+?

Answer 20

green

Question 21

during the addition of ammonia to aqueous copper sulphate, a ligand swap occurs with water, what observations would be expected?

Answer 21

• given that ammonia is higher on the spectrochemical series
• higher energy light will be absorbed
• such as blue
• therefore the solution will change to the complementary colour of orange

Question 22

define isoelectronic

Answer 22

having the same numbers of electrons or the same electronic structure

Question 23

explain why [Ti(H2O)6]3+, and other complex ions alike, display colours (3)

Answer 23

• ligands cause splitting of the 3d orbital into 2 energy levels
• energy from visible light promotes an electron from a lower energy level to a igher energy level
• the energy absorbed is in the visible regioin of the spectrum
• so the complementary colour is expressed

Question 24

concentrated ammonia was added to [Ti(H2O)6]3+ in a solution. How would this impact the wavelength of light absorbed by the solution? (2)

Answer 24

• as the ammonia is concentrated, it would displace/ replace the H2O ligands with NH3 ligands
• NH3 is further up the electrochemical series than H2O
• therefore, higher energy light is absorbed with a lower wavelength

Question 25

explain why zinc-containing compounds are generally not used as dyes in this way (2)

Answer 25

• Zn forms Zn^2+ ion which has no unpaired d electrons
• therefore, no light energy is absorbed/ no electrons are promoted