Transition Metals

Question 1

A transition element is a ____________ _______ which forms ______________ s_____ s_____ ion in which there is a ________-_______ _ subshell.

Answer 1

A transition element is a d-block element which forms at least one stable simple ion in which there is a partially filled d subshell.

Question 2

Why atomic radii of transition elements smaller than typical S block element, Ca?

Answer 2

Increase in nuclear charge
Shielding effect by inner shells of electrons remain relatively constant as 3d electrons provide relatively poor screening effect.
Effective nuclear charge higher for transition elements than Ca.
Stronger electrostatic attraction between the valence electrons and nucleus -> smaller atomic radius for transition elements.

Question 3

Why ionic radii of transition elements smaller than corresponding atomic radii?

Answer 3

4s electrons were removed to form the ions

Ions have one less PQ shell compared to atoms.

Question 4

Name and describe one important chemical property of transition elements?

Answer 4

Variable oxidation states.

Can form compounds in a range of oxidation states due to

CLOSE similarity in energy of 3d and 4s electrons.

Question 5

What is a ligand?

An ___ or ________ which contains at least one atom bearing one ____ of e________ which can be donated into the energetically _____________ vacant orbital of the central _____atom or ion forming a ______________ (dative) bond.

Answer 5

Ion or molecule (Cl-, OH-,H2O, NH3 etc)
Bearing ONE PAIR OF ELECTRONS
which can be DONATED into energetically ACCESSIBLE vacant orbital of central METAL ATOM OR ION
Forming a co-ordinate (dative) bond

Question 6

Occurrence of colour in transition metal complexes -> explain how?

Answer 6

Complex ion initially has one set of 3d orbital, degenerate, a happy family. THEN:

📌presence of ligands (slut)
📌3d orbitals split into 2 sets of orbitals with different energies.
📌Difference in energies between 2 sets of 3d orbitals relatively small
📌When an electron moves from orbital of lower energy to partially filled/empty d orbitals of higher energy
📌absorb radiation from the visible electromagnetic spectrum
📌colour observed is complementary of colour absorbed.

Question 7

What must metals possess to display colour?

Answer 7

1. At least one d electron

2. An empty or partially filled upper level to accommodate d electron to be promoted

Question 8

Steps to check if something is a transition element?

Answer 8

1. List electronic configuration.
2. See if they have partially filled d orbitals!
3. **some oxidation states of some transition metals ARE NOT TRANSITION ELEMENTS.
4. Sc and Zn do not have ions with partially-filled 3d subshells-> not transition elements.
5. Cu+ NOT, Cu2+ is! (hence former colourless, latter has colour)

Question 9

Factors affecting colour of complexes

Dependent on energy gap between two sets of d orbitals, in turn dependent on

1) _______ of central metal atom or ion
2) _______ of ligand

Answer 9

1. NATURE of central metal atom or ion -> different metals different energy gaps + oxidation state -> compounds of same element in different oxidation states show different colours
2. NATURE of ligand
   Energy gap between two groups of d orbitals depend on type of ligand -> different ligands split d orbitals by different amount (extent).

Question 10

Ligand exchange reactions are??

Answer 10

Very duh, just look at equation, one displaces the other. (Oxidation state does change!!)

Question 11

What is Ks? Give the equation and meaning.

Answer 11

Ks is like Kp/Kc, concentration of products over reactants. Same thing, coefficient is power.

It is the inherent tendency of a particular ligand to replace water in the aqua-complex.

Higher Ks -> stronger binding ligand.

Question 12

Are ligand exchange reactions reversible? What is the consequence?

Answer 12

Yes!

Relative concentrations of ligand will influence the ligand exchange. (LCP)

Question 13

Effect of ligand exchange on E(nought) values? Think of Fe example.

Other ligands replace water ligands (H2O) in an aqua complex -> can cause LARGE CHANGES in electrode potential values.

Answer 13

Replacing H2O with stronger binding CN- causes E(naught) for the Fe3+/Fe2+ system to become less positive -> means more favourable for oxidation, less for reduction -> Fe3+ a weaker oxidising agent.

Question 14

What is haemoglobin?

Answer 14

Red pigment in blood, carries oxygen from lungs to cells of body.

Question 15

What are the bitchy, evil, ligands?? Aka poisonous.

Explain in relation to haemoglobin.

Answer 15

CN- and CO

Can replace water molecule of haemoglobin, strongly and often IRREVERSIBLY adsorbed at this site, destroys haemoglobin’s oxygen-carrying capacity.

Question 16

Reactions of transition metal complexes

Chromium (Cr)

Is it acidic or basic? Reacts with carbonates to give? Reacts with metals to give?

When NaOH added to Cr3+ solution what is formed? In excess how?

Answer 16

It is acidic. Rx with carbonate to give CO2 and with metals to give H2 (g).

NaOH (aq) to Cr3+ -> grey green ppt formed, dissolved in excess NaOH (aq) to give dark green solution.

Question 17

Ligand exchange reaction between excess Cl- (aq) and copper (II) solution? What forms?

Answer 17

YELLOW COMPLEX of [CuCl4]2-

Question 18

Addition of I- (aq) to copper (II) solution results in?

Answer 18

Redox reaction

2Cu2+(aq) + 4I- (aq) -> 2CuI (s) + I2 (aq)

The CuI is the off-white ppt, I2 is the brown solution.

Question 19

A transition element is a ____________ element which forms ______________ stable simple ion in which there is a ________-_______ d subshell.

Answer 19

D-block
At least one
Partially-filled

Question 20

Chromium transition metal

Ion of chromium (aq)??

Answer 20

[Cr(H2O)6]^3+ (aq)

Question 21

NaOH (aq) added to chromium (III) solution!!

What colour is first formed? Give eqn.

Dissolves in excess NaOH (aq) to give what colour?? Give eqn.

Answer 21

Grey-green ppt : [Cr(H2O)6]3+ (aq) + 3OH- (aq) -> 👉🏻Cr(OH)3 (s)👈🏻 + 6H2O (l)

👉🏻Cr(OH)3 (s) 👈🏻+ 3OH- (aq) (reversible) [Cr(OH)6]3- (aq)

Question 22

Yellow CrO4^2- (aq) and orange Cr2O7^2- (aq) can be converted to each other depending on pH of solution. Give EQNs.

Answer 22

Yellow CrO4^2-: need acid to convert to orange
2CrO4^2- (aq) + 2H+ (aq) Cr2O7^2- (aq) + H2O (l)

Orange need alkaline to convert to yellow
Cr2O7^2- (aq) + 2OH- (aq) 2CrO4^2- (aq) + H2O (l)

Question 23

What colour is Mn2+ (aq)?

Answer 23

Pink / colourless

Question 24

MnO4- is what colour?

Answer 24

Purple

Question 25

MnO4- reduced under slightly alkaline conditions to give MnO2 (s) which is what colour?

Answer 25

Dark brown.

Question 26

Aqueous fe3+ ion is acidic. True / false?

Answer 26

TRUE, [Fe(H2O)6]^3+ is acidic, reacts with carbonates to give carbon dioxide and metals to give hydrogen gas.

Equation to show that it is acidic:

[Fe(H2O)6]^3+ + H2O (l) [Fe(H2O)5(OH)]2+ (aq) + H3O+ (aq)

Question 27

Which is stronger and more stable, polydentate or monodentate ligands?

Answer 27

Polydentate -> more coordinate / dative bonds, can hold on to central metal atom/ion better -> more stable.

Question 28

When NaOH(aq) added to Fe2+ solution what happens? What ppt formed? What happens if it is left in the air?

Answer 28

[Fe(H2O)6]^2+ (aq) + 2OH- (aq) -> Fe(OH)2 (s) + 6H2O (l)

A GREEN ppt is formed (red light absorbed). Upon leaving in air, green ppt turns reddish brown.

4Fe(OH)2 + O2 + 2H2O -> 4Fe(OH)3 (green ppt is oxidised, Fe2+ to Fe3+)

Question 29

CN- added to Fe2+ solution -> what occurs?

Answer 29

Ligand exchange reaction.

[Fe(H2O)6]2+ (aq) + 6CN- (aq) [Fe(CN)6]^4- (aq) + 6H2O (l)

Question 30

SCN- (aq) added to Fe3+ solution -> what occurs?

Answer 30

Ligand exchange reaction.

[Fe(H2O)6]3+ (aq) + SCN- (aq) [Fe(SCN)(H2O)5]^2+ (aq) + H2O (l) (blood red complex formed) 😡

Question 31

What colour is copper solid?

Answer 31

💞💞💞💞💞💞💞💞💞 PINK 💞💞💞💞💞💞💞💞

Question 32

Copper (II) Cu2+ salts dissolve in water to give what solutions? what colour?

Answer 32

💎💎💎 BLUE 💎💎💎 SOLUTIONS!!!!!!!!!!

What ion is formed? [Cu(H2O)6]2+ (aq)

Question 33

When NH3 (aq) is added to the [Cu(H2O)6]2+ (aq) what is formed initially? In excess?

Answer 33

First derive your OH- ions from NH3 dissolved in water:
NH3 (aq) + H2O (l) NH4+ (aq) + OH- (aq)

Then realise that the [Cu(H2O)6]2+ (aq) react with the OH-!!

A 💎💎💎 BLUE 💎💎💎 precipitate of Cu(OH)2 is formed.
[Cu(H2O)6]^2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s) + 6H2O (l)

Upon excess NH3 (aq), precipitate DISSOLVES, gives 💙💙dark blue 💙💙 solution.

Cu(OH)2 (s) + 4NH3 (aq) + 2H2O (l) [Cu(NH3)4(H2O)2]^2+ (aq) + 2OH- (aq)

Question 34

Addition of excess Cl- (aq) to copper (II) solution results in what reaction? Formation of?

Answer 34

LIGAND EXCHANGE REACTION.

[CuCl4]^2- (aq) formed is 💛 yellow 💛 complex.
[Cu(H2O)6]^2+ (Aq) + 4Cl- (aq) [CuCl4]^2- (aq) + 6H2O (l)

Question 35

Addition of I- (aq) to copper (II) solution results in what reaction? What ppt? What OBSERVATIONS?

Answer 35

Redox reaction! Our FAVOURITE because it benefits one at the cost of another! 🌝

2Cu2+ (aq) + 4Cl- (aq) -> 2CuI (s) + I2 (aq)
CuI (haha, cui sia) is an 🐑 off-white🐑 ppt (because Cu+ is not transition element anymore), I2 is 🍩 brown 🍩 solution.

Question 36

What are the complementary colours!

Answer 36

🌹 Red - Green 🌵 (christmas)
💙 Blue - Orange 🎃 (poqing)
💛 Yellow - Purple 💜(happiness)

Question 37

When Cl- (aq) added to silver (I) Ag+ solution, what is formed? Dissolves in NH3 (aq) to give?

Answer 37

Ag+ (aq) + Cl- (aq) -> AgCl (s) which is white ppt

Ppt dissolves in NH3 (aq) to give colourless solution

AgCl (s) + 2NH3 (aq) [Ag(NH3)2]+ + Cl- (aq)