Unit 1-Transition Metals

Question 1

Why are transition metals known as d block elements?

Answer 1

The d block transition metals are metals with an incomplete d subshell in at least one of their ions.

Question 2

Explain why Copper and Chromium appear not to follow the aufbau principle (orbitals are filled in order of increasing energy).

Answer 2

Chromium [Ar] 3d5 4s1

Copper [Ar] 3d10 4s1

Half-filled or fully filled d orbitals have a special stability. However, whenever transition metals form ions electrons are lost first from the outermost subshell the 4s.

Question 3

What is the electron configuration of Co²⁺ ?

Answer 3

1s22s22p63s23p63d7

Question 4

Explain why Scandium 3+ and Zinc 2+ ions are often considered not to be transition metals.

Answer 4

Scandium only forms 3+ ions and Zinc only forms 2+ ions. Neither of these result in an incomplete d subshell, therefore do not fit the definition of a transition metal.

Question 5

Consider the electronic configurations of the Fe²⁺ and Fe³⁺ ions in terms of orbital box notation. Explain why Fe(III) compounds are more stable than Fe(II) compounds.

Answer 5

Fe³⁺ ions would have a half-filled d subshell which is stable.

Question 6

What are the oxidation states of sulfur in H₂S, S₈ (elementary sulphur), SO₂ and SO₄^2-

Answer 6

H₂S, S₈ (elementary sulphur), SO₂, SO₃, and H₂SO₄

-2, 0, +4 and +6.

Question 7

Define oxidation and reduction in terms of oxidation number

Answer 7

OXIDATION can be defined as an increase in oxidation number, while REDUCTION can be defined as a decrease in oxidation number.

Question 8

What is a transition metal complex?

Answer 8

A complex consists of a central metal ion surrounded by ligands

Question 9

What is a ligand and how does it bond to a TM?

Answer 9

Ligands are electron donors which may be negative ions or molecules with non-bonding pairs of electrons.

Question 10

What is meant by a dative bond?

What is co-ordination number?

Answer 10

a covalent bond (a shared pair of electrons) in which both electrons come from the same atom.

and

the number of bonds attached to the TM

Question 11

How many pairs of electrons do each of the following types of ligands donate?

i) monodentate
ii) bidentate
iii) polydentate

Answer 11

i) one
ii) two
iii) more than one

Question 12

one nickel(II) ion will form six bonds with one ‘molecule’ of EDTA

i) What type of ligand is EDTA
ii) what is the coordination number of nickel?

Answer 12

i) polydentate or hexadentate
ii) 6

Question 13

i) Name this complex
ii) What its coordiation number of the transition metal ion
iii) What is the oxidation state of the metal ion

[Co(OH₂)₆]Cl₂

Answer 13

i) Hexaaquacobalt(II)
ii) 6
iii) +2

Question 14

Na[CrF₄]

i) Name the complex in the square brackets
ii) What its coordiation number of the transition metal ion
iii) What is the oxidation state of the metal ion

Answer 14

i) tetrafluorochromate(III)
ii) 4
iii) +3

We need 1 Na⁺ to balance charge on complex.

If we have 4 F^- then this means that the chromate

Question 15

i) Name this complex
ii) What its coordiation number of the transition metal ion
iii) What is the oxidation state of the metal ion

[Co(H₂O)₆]Cl₂

Answer 15

i) Hexaaquacobalt(II) chloride
ii) 6
iii) +2

Question 16

What name is given to AOs which have the same energy?

Answer 16

Degenerate

Question 17

What happens to the 5 degenerate d AOs when a ligang(s) approach a TM ion?

Answer 17

They split:

_ _

_ _ _

Question 18

Describe how TM complexes are coloured

Answer 18

Light is absorbed and electrons are promoted to a d orbital of higher energy

The complimentary colour is observed which is in the visible or UV regions

Question 19

Different ligands can cause different splitting between the d AOs.

What is the relationship between E and wavelength?

Answer 19

As E increases, wavelength decreases.

Question 20

A use of TMs is

Answer 20

Catalysts

Question 21

What is a:

• heterogeneous catalyst
• homogeneous catalyst

Answer 21

a catalyst in the different physical state to the reactants

a catalyst in the same physical state to the reactants

Question 22

How does a catalyst work?

Answer 22

reactants are adsorbed onto the active site of the catalyst forming an activated complex (because the TM has an unfilled d AO) which lowers the activation energy