5.3.1 Transition Elements

Question 1

What is a transition element?

Answer 1

• a d-block element that forms at least one stable ion with an incomplete d-subshell

Question 2

What are the exception to the filling of sub shells for transition elements?

Answer 2

Chromium - 3d54s1 (instead of 3d44s2)
Copper - 3d104s1 (instead of 3d94s2)

Question 3

How do transition metals form ions?

Answer 3

• form positive ions and lose electrons
• lost from the 4s first and then the 3d
• 3d and 4s su shells are very close in energy and once they are occupied, repulsion between electrons causes the 4s to have a higher energy than the 3d

Question 4

Are scandium and zinc transition metals?

Answer 4

• Sc forms 3+ ion in which the d-sub shell is empty
• Zn forms a 2+ ion in which the d-sub shell is full
• don’t form ions with incomplete d sub shells - not transition metals

Question 5

What are the physical properties of transition metals?

Answer 5

• similar atomic radius, high densities and high melting points
• metallic bonding: a giant lattice of regularly arranged positive ions in a sea of delocalised electrons with strong electrostatic attractions between them

Question 6

What are the chemical properties of transition metals?

Answer 6

• form compounds in which the transition metal has variable oxidation states
• form coloured solutions when dissolved in water
• frequently catalyse chemical reactions
• form complex ions

Question 7

Examples of variable oxidation states

Answer 7

• copper +1 and +2
• iron +2 and +3

Question 8

Examples of coloured solutions

Answer 8

• copper sulphate is blue
• iron (II) sulphate is pale green

Question 9

Examples of catalysts

Answer 9

• iron in the Haber process
• manganese oxide in the decomposition of hydrogen peroxide

Question 10

What is a complex ion?

Answer 10

• a central transition metal bonded to one or more ligands by coordinate bonds

Question 11

What is a ligand?

Answer 11

• an ion or molecule with a lone pair of electrons that can be donated to a transition metal to form a co-ordinate bond

Question 12

What is the coordination number?

Answer 12

• the total number of coordinate bonds between a central metal ion and its ligands

Question 13

What is a monodentate ligand?

Answer 13

• a ligand that donates one pair of electrons to the central metal ion

Question 14

What is a bidentate ligand?

Answer 14

• a ligand that donates 2 lone pairs of electrons to the central transition metal ion, forming two coordinate bonds

Question 15

What shape are complex ions with 6 coordination number?

Answer 15

• octahedral
• 90*

Question 16

What shape are complex ions with 4 coordination number?

Answer 16

• tetrahedral or square planar
• 109.5* or 90*
• nickel, palladium and potassium are square planar

Question 17

What are stereoisomers?

Answer 17

• same molecular and structural formula and different arrangement of atoms in space

Question 18

What is the cis isomer?

Answer 18

A-M-A bond angle 90*

Question 19

What is the trans isomer?

Answer 19

A-M-A bond angle 180*

Question 20

What are optical isomers?

Answer 20

• non-superimposable mirror images (no plane of symmetry)

Question 21

What complex ions show optical isomerism?

Answer 21

• octahedral metal with 2 bi and 2 mono ligands
• octahedral metal with 3 bi ligands

Question 22

What is the use of cisplatin in medicine?

Answer 22

• anti-cancer drug
• binds to DNA and prevents cell division, killing cancer cells

Question 23

What is ligand substitution?

Answer 23

• a reaction in which one ligand in a complex is replaced by another ligand

Question 24

What is ligand substitution reaction from [Cu(H2O)6]2+?

Answer 24

[Cu(H2O)6]2+ + little NH3 -> Cu(OH)2
blue solution blue ppt

[Cu(H2O)6]2+ + excess NH3 -> [Cu(NH3)4(H2O)2]2+
blue solution deep blue solution

[Cu(H2O)6]2+ + Cl- -> [CuCl4]2-
blue solution yellow solution

Question 25

Why might the solution appear green?

Answer 25

• contains a mixture of complex ions in equilibrium
• position and colour can be changed by adding water or chlorine

Question 26

What is the ligand substitution reaction from [Cr(H2O)6]3+?

Answer 26

[Cr(H2O)6] + little NH3 -> Cr(OH)3
violet solution grey/green ppt

[Cr(H2O)6] + excess NH3 -> [Cr(NH3)6]2+
violet solution purple solution

Question 27

What is the biochemical importance of iron?

Answer 27

• haemoglobin contains haem groups which contain iron ion
• oxygen acts as a ligand and binds reversibly to Fe2+
• oxygen and CO both use same binding site
• CO ligands bind more strongly and irreversibly
• reduces ability of blood to transport oxygen around the body

Question 28

Copper colours

Answer 28

• Cu2+(aq) blue solution
• Cu(OH)2 blue precipitate

Question 29

Iron colours

Answer 29

• Fe2+(aq) pale green solution
• Fe(OH)2 dark green precipitate (standing red-brown)
• Fe3+(aq) yellow solution
• Fe(OH)3 orange-brown ppt

Question 30

Manganese colours

Answer 30

• Mn2+ (aq) pale pink (dilute colourless)
• Mn(OH)2 light brown ppt

Question 31

Chromium colours

Answer 31

• Cr3+(aq) violet solution
• Cr(OH)3 grey-green ppt
• with excess NaOH, ppt will dissolve into green solution