A2- Transition Metals

Question 1

What are 4 general properties of transition metals?

Answer 1

• form coloured ions
• form complexes
• variable oxidation states
• act as catalysts

Question 2

What is a Ligand?

Answer 2

a central metal atom or ion surrounded by ligands

Question 3

What is meant by the term coordination number?

Answer 3

the number of co-ordinate binds to the central metal atom or ion

Question 4

What shape and bond angle does a complex with H2O ligands have?

Answer 4

Octahedral, 90

Question 5

What shape and bond angle does a complex made with Cl have?

Answer 5

tetrahedral, 109.5

Question 6

What is a bidentate ligand? give an example

Answer 6

a ligand that forms 2 coordinate bonds with the central metal atom
- diaminoethane
- ethanedioate

Question 7

Why do transition metals share the same 4 general properties?

Answer 7

incomplete d-subshell

Question 8

Why does Cl- form a tetrahedral complex?

Answer 8

larger ions

Question 9

Give 3 examples of monodentate ligands

Answer 9

H2O, NH3, Cl-

Question 10

What is a monodentate ligand?

Answer 10

a ligand that makes only one coordinate bond to the central metal ion or atom

Question 11

Give an example of a multidentate ligand

Answer 11

EDTA4-

Question 12

Why are some transition metals coloured?

Answer 12

some wavelengths of light are absorbed and the remaining are transmitted or reflected

Question 13

What do blue compounds absorb and reflect?

Answer 13

absorbs all parts of the spectrum except from blue light which it reflects

Question 14

What happens to d electrons when light is absorbed?

Answer 14

They gain energy and move from a ground state to an excited state

Question 15

How do d electrons relax back to the ground state?

Answer 15

releasing thermal energy

Question 16

What 2 equations give the energy difference between ground and excited states?

Answer 16

change in energy = hc/wavelength
change in energy = hv

Question 17

What factors change the difference in energy?

Answer 17

• oxidation state
• coordination number
• ligand

Question 18

Why are transition metal compounds coloured?

Answer 18

• incomplete d-subshells
• so electrons can move between orbitals
• in compounds, d-orbitals have slightly different energy levels

Question 19

What can colorimetry be used to determine?

Answer 19

concentration of coloured ions

Question 20

How is colorimetry carried out to find concentration of coloured ions?

Answer 20

1) series of dilutions, with known concentrations
2) find absorbance using colorimeter
3) plot graph of absorbance vs conc and draw line of best fit
4) find absorbance of unknown sample
5) use graph

Question 21

What are ligand substitution reactions?

Answer 21

reactions where ligands around a complex ion are substituted by other ligands

Question 22

What is a complete ligand substitution with no change in coordination number?

Answer 22

a reaction where all ligands are substituted by new ones. Ligands must be a similar size

Question 23

Why do complete ligand substitutions with no change in coordination number have small enthalpy changes?

Answer 23

small bond energies of ligands are similar

Question 24

What is a complete ligand substitution with a change in coordination number?

Answer 24

a reaction where all ligands are substituted by new ones, ligands are different size

Question 25

What is an incomplete ligand substitution with no change in coordination number?

Answer 25

only some ligands substituted but number of coordinate bonds stays the same

Question 26

Why do multidentate ligands form thermodynamically stable compounds?

Answer 26

• very small enthalpy change as 6 C-O are broken and 6 are formed
• large entropy change as more species are produced
• very negative free energy change