5.3 Transition Metals

Question 1

Define a transition metal

Answer 1

-d-block elements that have an ion with an incomplete d-sub shell

Question 2

Why are scandium and zinc not classed as transition metals?

Answer 2

-because they do not have any ions with partially filled d-orbitals
-scandium only forms Sc+3 ion in which d-orbitals are empty
-zinc forms only Zn2+ ion in which d-orbitals are full

Question 3

When writing electron configurations in what order should you write the 3d and 4s sub shell?

Answer 3

The 4s sub shell has a lower energy than the3d sub shell
This means that the 4s orbital fills before the orbitals in the 3D sub shell

Question 4

What are the two transition metals do not follow the rules for filling sub shells?

Answer 4

Chromium-the five 3d-orbitals and the 4s orbital all contain one electron with no orbital being completely filled.
Copper-the five 3d-orbitals are full but there is only one electron in the 4s-orbital

Question 5

Write out the electron configuration for chromium

Answer 5

1s2 2s2 2p6 3s2 3p6 4s1 3d5

Question 6

Write out the electron configuration for copper

Answer 6

1s2 2s2 2p6 3s2 3p6 4s1 3d10

Question 7

When forming positive ions from transition metals the ___ electrons are lost before the ____ electrons.

Answer 7

4s orbital
3d orbitals
As once the electrons occupy the orbitals the 4s electrons have a higher energy

(FIRST IN FIRST OUT)

Question 8

Transition elements exist in more than one …

Answer 8

-oxidation state
-e.g Fe2+ and Fe3+
-> Cr2+ and Cr3+ and Cr6+
->Mn2+ and Mn7+

Question 9

In what two ways to transition metals behave as catalysts?

Answer 9

->transition metals provide a surface on which a reaction can take place. Reactants are absorbed onto the surface of the metal and held in place while a reaction occurs. After the reaction, the products are desorbed and the metal remains unchanged
->transition metal ions have the ability to change their oxidation states by gaining or losing electrons. They then bind to reactants, forming intermediates as part of a chemical pathway, often with a lower activation energy which speeds up the reaction

Question 11

What are the benefits and risks of transition metals catalysts?

Answer 11

-they reduce the amount of energy needed to make a reaction occur
-transition metals compounds can be toxic, when substances bind to the active site and stop the transition metal catalysts from working, the catalysts can no longer be used and must be disposed of in a way that causes no pollution

Question 12

List two examples of the catalytic behaviour of transition metals

Answer 12

->hydrogen peroxide decomposes slowly at room temperature and pressure into water and oxygen
(2H2O2(aq) -> 2H2O(l) + O2(g) )
-manganese(IV) oxide, MnO2 is a suitable catalyst, in which manganese has a 4+ oxidation state
-this reaction is used as a way to prepare oxygen gas

->zinc granules will react with dilute sulfuric acid to form hydrogen and zinc sulfate, copper sulfate acts as a catalyst, copper has a 2+ oxidation state in copper sulfate
-this reaction is used to produce hydrogen gas

Question 13

Define the term ligand

Answer 13

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

Question 14

Define the term complex ion

Answer 14

-> a transition metal ion bonded to one or more ligands by coordinate bonds (dative covalent bonds)

Question 15

Define the term coordination number

Answer 15

-> the total number of COORDINATE bonds formed between a central metal ion and its ligands

Question 16

Ligands are _________ ________ as they are electrons donors

Answer 16

Lewis bases

Question 17

List 6 common ligands, state their formula and charge

Answer 17

Question 18

What are bidentate ligands?

Answer 18

-> they each form 2 coordinate bonds

Question 19

Explain why ethane-1,2-diamine can act as a bidentate ligand

Answer 19

-nitrogen atoms both have a lone pair of electrons which can be donated to a metal ion and form 2 coordinate bonds

Question 20

What is an example of a bidentate ligand?

Answer 20

-> NH2CH2CH2NH2 (‘en’)

Question 21

List three examples of monodentate ligands

Answer 21

• H2O
  -Cl-
  -NH3

Question 22

Draw out an example of a complex ion with an octahedral shape
What is its coordinate number

Answer 22

-many hexaaqua complexes form octahedral shape
-they have a coordinate number of six
E.g.

Question 23

Draw out [CuCl4]2- and [CoCl4]2-
What shape are they ?

Answer 23

Tetrahedral
->many tetrachloro complexes form tetrahedral shape as chloride ligands are so large only four can fit around the transition metal ion

Question 24

Draw out a complex ion with the square planar shape
What is an example of a complex ion with this shape?

Answer 24

-complexes of Pt often form this shape
E.g. cis-platin, Pt(NH3)2Cl2

Question 25

How is cis-platin used as an anti-cancer drug? What are the risks of chemotherapy?

Answer 25

-cis-platin is an anti-cancer drug -it binds to DNA preventing cell division, this is the basis for chemotherapy treatment -chemotherapy has risks of unpleasant side effects e.g. severe sickness, hair loss and fatigue

Question 26

What is a ligand substitution reaction?

Answer 26

-a reaction in which one ligand in a complex ion is replaced by another ligand

Question 27

Write the equation for the ligand substitution reaction that happens when an excess of aqueous ammonia solution is added to [Cu(H2O)6]^2+ include colour changes.

Answer 27

-on addition of a small amount of ammonia a pale blue precipitate of copper (II) hydroxide Cu(OH)2 forms, as ammonia acts as an alkali -on addition of EXCESS aqueous ammonia the pale blue precipitate dissolves and a deep blue solution is formed containing [Cu(NH3)4(H2O)2]^2+ ions

Question 28

Write the equation for the ligand substitution reaction that happens when concentrated hydrochloric acid is added to an aqueous solution containing copper (II) ions, [Cu(H2O)6]^2+ Include colour changes

Answer 28

When concentrated hydrochloric acid is added to an aqueous solution containing copper (II) ions, the pale blue solution initially forms a green solution before finally turning yellow This reaction exists in equilibrium and can be reversed by adding water to the yellow solution to return it to the original pale blue colour

Question 29

Write the equation for the ligand substitution reaction that occurs when ammonia is added to an aqueous solution of chromium(III) containing [Cr(H2O)6]^3+ Include colour changes

Answer 29

-an aqueous solution of chromium(III) contains [Cr(H2O)6]^3+ complex ions and has a grey-green or dark green colour -when a small amount of ammonia is added hydrogen ions are pulled off the water ligands this produces a green precipitate of [Cr(H2O)3(OH)3] -when EXCESS ammonia is added, some of the green precipitate re-dissolves to form a DARK GREEN solution. This is more noticeable when concentrated ammonia is used Balanced chemical equation [Cr(H2O)6]^3+ + 6NH3 ⇌ [Cr(NH3)6]^3+ + 6H2O

Question 30

Describe the biochemical importance of iron in heamoglobin

Answer 30

-heamoglobin is a complex protein composed of four polypeptide chains -each protein chain contains four non-protein components called haem groups, each haem group has an Fe^2+ ion at its centre- oxygen can reversibly bind to the Fe^2+ ion -this allows heamoglobin to carry out its function of transporting oxygen around the body Around the Fe2+ ion in a haem group they are: ->four coordinate bonds between the Fe2+ ion and the nitrogen atoms in the haem structure ->a coordinate bond is formed to the protein globin ->a coordinate bond can form to an oxygen molecule which is then transported

Question 31

Can carbon monoxide bond to haemoglobin?

Answer 31

-carbon monoxide and oxygen can both bind to haemoglobin at the same place -carbon monoxide binds more strongly to the haemoglobin than oxygen -if both carbon monoxide and oxygen are present carbon monoxide will bind to haemoglobin -leaving fewer haemoglobin molecules to bind to oxygen molecules- tissues can be starved of oxygen because less oxygen is carried around the body -this is an example of ligand substitution -the reaction is not reversible for carbon monoxide - low levels of carbon monoxide in blood can cause headaches, nausea and potential suffocation. High levels can cause death -carbon monoxide is odourless and colourless and formed during incomplete combustion of carbon containing fuels