13. Periodicity

Question 1

Define transition element

Answer 1

An element that forms at least one stable ion with a partially filled d sub-level

Question 2

Define complex ion

Answer 2

A central metal ion closely bonded by coordinate covalent bonds to a cluster of molecules or anions called ligands

Question 3

Define ligands

Answer 3

Aions or molecules that have one at least one lone pair of electrons to form a coordinate covalent bond with the central metal ion

Question 4

Define coordination number

Answer 4

The number of coordinate bonds formed between the ligands and the transition metal ion

Question 5

Define ligand exchange reaction

Answer 5

A stronger ligand can replace a weaker ligand from a cation complex in a ligand exchange reaction

Question 6

Explain the periodicity trend for atomic radii

Answer 6

Nuclear charge increases but there are also additional electrons added → Not much change in effective nuclear charge & radius

Question 7

Explain the periodicity trend for density

Answer 7

Gradual increase due to increase in relative atomic mass & decrease in volume

Question 8

Why do transition elements have higher boiling points compared to s-block elements?

Answer 8

Strong metallic bonding due to the availability of both 3d and 4s electrons for delocalisation

Question 9

Explain the periodic trend for ionisation energy

Answer 9

Small increase in 1st & 2nd IE, but greater increase in the rest of the IEs → Shielding effect results in not much difference in effective nuclear charge
After 1st & 2nd IE, d sub-level electrons are now involved → Poorer shielding effect → Increase in effective nuclear charge

Question 10

Explain the relatively lower melting point of manganese

Answer 10

It’s stable due to its half-filled 3d electrons, which lowers the availability of valence ectrons for delocalisation → Weaker metallic bond

Question 11

Lower expected values of 3rd IE for iron and 4th IE for cobalt

Answer 11

Removing paired electron is easier than removing unpaired due to inter-electronic repulsion

Question 12

Why do transition metals have variable oxidation states?

Answer 12

Small energy diff. between 3d & 4s sub-levels → Able to use variable number of electrons for bonding → Variable oxidation states

Question 13

What causes paramagnetism and what are its effects?

Answer 13

Unpaired electrons. Paramagnetic substances are attracted by a magnetic field

Question 14

What causes diamagnetism and what do diamagnetic substances do?

Answer 14

Paired electrons. They are repelled slightly by a magnetic field.

Question 15

Diff. between cis-trans isomers?

Answer 15

• Cis: Same side

- Trans: Different side

Question 16

Explain why transition metal complexes are coloured

Answer 16

• The electronic configuration of ___ is ___.
• In a transition metal complex, d orbital splitting occurs, when the d orbitals are split into 2 groups due to the ability of the ligands to split them into 2 different sets of energy levels.
• When a d-electron absorbs this light, it will be promoted from the lower enery level to the higher energy level termed, d-d electron transition.
• The colour of the complex is complementary to the colour of light absorbed.

Question 17

When is a complex colourless/white?

Answer 17

1. Empty d-orbitals or completely filled d-orbitals → No d-d electron transition available
2. Energy gap does not fall within visible light spectrum

Question 18

What are the 4 factors that affect the energy gap, and hence the colour of complexes?

Answer 18

1. Metal ion
   
   • Higher nuclear charge → More effective interaction with ligand → Larger energy gap → Smaller wavelength absorbed → Longer wavelength observed
2. Number of d electrons
   
   • More electrons → Greater strength of interaction → Smaller wavelength absorbed
3. Nature of ligand
   
   • Higher charge density → Larger energy gap → Smaller wavelength absorbed
4. Geometry of complex
   
   • Orientation of d orbitals and ligand