Transition Elements

Question 1

How do you work out the electronic configuration of atoms and ions in the d-block of the periodic table?

Answer 1

4s subshell fills before 3d subshell
From Sc-Zn, the 3d subshell is being filled
Exceptions are chromium, Cr which has (Ar)4s(1)3d(5) and copper, Cu which has (Ar)4s(1)3d(10)
When making ions, the 4s electrons are lost first

Question 2

Define transition elements

Answer 2

D-block elements that form a stable ion with an incomplete d sub-shell. Note: scandium and zinc are d block elements but are not transition elements

Question 3

What are the properties of transition metals?

Answer 3

Exist in more than 1 oxidation state for each element in its compounds
Form coloured ions
Act as catalysts as elements or in compounds

Question 4

How can transition elements exist in more than one oxidation state?

Answer 4

All form 2+ ions by losing the 4s electrons
As 4s and 3d subshells are so similar in energy level, the 3d electrons can also be lost and a stable ion formed. The highest oxidation states formed are +6 in Chromium and +7 in manganate. These are powerful oxidising agents.

Question 5

What colour are the oxidation states of Vanadium?

Answer 5

+2: lilac
+3: green
+4: blue
+5: yellow

Question 6

What colour are the oxidation states of Chromium?

Answer 6

+2: dark blue
+3: green
+4 and +5: colourless
+6: orange

Question 7

What colour are the oxidation states of Manganese?

Answer 7

+2: pale pink
+3 - +6: colourless
+7: purple

Question 8

What colour are the oxidation states of Iron?

Answer 8

+2: pale green
+3: pale yellow
+4 - +6: colourless

Question 9

What colour are the oxidation states of Cobalt?

Answer 9

+2: pink
+3: olive green
+4 and +5: colourless

Question 10

What colour are the oxidation states of Copper?

Answer 10

+2: blue

+3: colourless

Question 11

How do transition metals act as catalysts?

Answer 11

Either - provide a surface for the reaction to take place on: adsorbtion of reactants onto the surface of the metal and held in place while a reaction occurs
Or - change in oxidation states by gain/loss of electrons, forming intermediates as part of a chemical pathway with a lower activation energy

Question 12

What are the observations and the ionic equation for cobalt ions reacting with NaOH?

Answer 12

Observations: pink solution containing Co(2+) forms blue precipitate that turns beige in the presence of air
Equation: Co(2+)aq + 2OH(-)aq -> Co(OH)2s

Question 13

What are the observations and the ionic equation for copper ions reacting with NaOH?

Answer 13

Observations: pale blue solution containing Cu(2+) forms a pale blue precipitate
Equation: Cu(2+)aq + 2OH(-)aq -> Cu(OH)2s

Question 14

What are the observations and the ionic equation for iron (II) ions reacting with NaOH?

Answer 14

Observations: pale green solution containing Fe(2+) forms a green precipitate that turns rusty brown in presence of air (Fe(2+) oxidised to Fe(3+))
Equation: Fe(2+)aq + 2OH(-)aq -> Fe(OH)2s

Question 15

What are the observations and the ionic equation for iron (III) ions reacting with NaOH?

Answer 15

Observations: pale yellow solution containing Fe(3+) forms a rusty brown precipitate
Equation: Fe(3+)aq + 3OH(-)aq -> Fe(OH)3s

Question 16

Define ligand

Answer 16

A molecule or ion that can donate a pair of electrons with the transition metal ion to form a coordinate bond

Question 17

Define complex ion

Answer 17

A transition metal ion bonded to one or more ligands by coordinate bonds

Question 18

Define coordination number

Answer 18

The total number of coordinate bonds formed between a central metal ion and its ligands

Question 19

What shape does a transition metal that has formed 6 coordinate bonds take?

Answer 19

Octahedral, with 90* between each bond. An example of one like this would be (Fe(H2O)6)2+

Question 20

Define bidentate ligand

Answer 20

A ligand that can donate 2 lone pairs of electrons to the central metal ion, forming 2 coordinate bonds. An example is ethane-1,2-diamine (en) which is NH(2)CH(2)CH(2)NH(2), where each nitrogen atom donates a pair of electrons

Question 21

What kinds of stereoisomerism to transition metals show?

Answer 21

Cis-trans isomerism: when have 2 different ligands and they are either together or opposite each other
Optical isomers: can occur when have 3 bidentate ligands, or the cis version from above

Question 22

How is cis-platin work as an anticancer drug?

Answer 22

Its the cis version of (PtCl(2)NH3(2))
Cis-platin binds to DNA of fast growing cancer cells, altering the DNA, preventing the cells from reproducing due to changes in the DNA structure. The cell’s repair mechanism then destroys the cancerous cell.

Question 23

What is ligand substitution?

Answer 23

The process in which one ligand in a complex ion is replaced by another ligand

Question 24

What are the observations and the equation when (Cu(H2O)6)2+ is converted into (Cu(NH3)4(H2O)2)2+?

Answer 24

Observations: pale blue solution forms a pale blue precipitate on addition of a small amount of ammonia (Cu(OH)2) which dissolves on addition of excess ammonia forming a deep blue solution
Equation: [Cu(H2O)6]2+(aq) + 4NH3(aq) [Cu(NH3)4(H2O)2]2+(aq) + 4H2O (l) Note: equilibrium reaction

Question 25

What are the observations and the equation when [Cu(H2O)6]2+ is converted into [CuCl4]2-?

Answer 25

Observations: pale blue solution changes colour to a yellow solution, passing through a green solution
Equation: [Cu(H2O)6]2+(aq) + 4Cl-(aq) [CuCl4]2-(aq) + 6H2O(l) Note: equilibrium reaction

Question 26

What are the observations and the equation when [Co(H2O)6]2+ is converted into [CoCl4]2-?

Answer 26

Observations: pale pink solution goes to a dark blue solution
Equation: [Co(H2O)6]2+(aq) + 4Cl-(aq) [CoCl4]2-(aq) + 6H2O(l)

Question 27

What is the biochemical importance of iron in haemoglobin?

Answer 27

An Fe2+ ion is at the centre of the haemoglobin molecule, with 4 coordinate bonds to nitrogen atoms in the haem structure; 1 coordinate bond to the globin protein and a space available to allow oxygen molecules to form a coordinate bond. In this way, oxygen can be carried around the body.
Carbon monoxide can also form a coordinate bond to Fe2+ in the same place as oxygen, and a much stronger bond is formed (ligand substitution reaction), resulting in CO being transported permanently around the body and the tissues being starved of oxygen.

Question 28

Define the term stability constant

Answer 28

The stability constant, K(stab), is the equilibrium constant for an equilibrium existing between a transition metal ion surrounded by water ligands and the complex formed when the same ion has undergone a ligand substitution.

Question 29

How is the stability constant calculated?

Answer 29

For reaction: [M(H2O)6]2+ + 6X [MX6]2+ + 6H2O
K(stab) = [[MX6]2+]/[[M(H2O)6]2+][X]^6
Same as K(c), just leave out the water

Question 30

What does the value of K(stab) tell us?

Answer 30

How stable the complex ion formed is: a large value for K(stab) means a stable ion is formed.