Chapter 24

Question 1

What are transition metals?

Answer 1

Elements with an incomplete d-subshell that can form at least one stable ion with an incomplete d-subshell.

Question 2

What two elements aren’t transition elements?

Answer 2

Scandium and Zinc.

Scandium only forms the ion Sc3+, configuration [Ar] 3d0

Zinc only forms the ion Zn2+, configuration [Ar] 3d10

Question 3

What fills or loses electrons first? 3d or 4s?

Answer 3

4s

Question 4

When writing them which is first 3d or 4s?

Answer 4

3d, 4s is always at the end.

Question 5

What is the electron configuration of Chromium?

Answer 5

Cr is [Ar] 3d5 4s1 not [Ar] 3d4 4s2

this is because its energetically more stable.

Question 6

What is the electron configuration of Copper?

Answer 6

Cu is [Ar] 3d10 4s1 not [Ar] 3d9 4s2

this is because its energetically more stable.

Question 7

What are some general properties of transition elements?

Answer 7

-Variable oxidation states
-Form complex ions
-Form coloured compounds
-Behave as catalysts

Question 8

What is a complex ion?

Answer 8

A molecule or ion, consisting of a central metal atom or ion, with a number of molecules or ions surrounding it

Question 9

What is a ligand?

Answer 9

A ligand is a molecule or ion that forms a co-ordinate bond with a transition metal by donating a pair of electrons to the bond.

A molecule or ion surrounding the central metal atom or ion.

Question 10

What colour is Cr3+

Answer 10

Green

Question 11

What colour is Cr 6+

Answer 11

Orange/yellow

Question 12

What colour is Mn2+

Answer 12

Pink

Question 13

What colour is Cu2+

Answer 13

Blue

Question 14

Why are transition metals good catalysts? How do they work?

Answer 14

Since transition elements can have variable oxidation states, they make excellent catalysts.

During catalysis, the transition element can change to various oxidation states by gaining electrons or donating electrons from reagents within the reaction.

Substances can also be adsorbed onto their surface and activated in the process.

Question 15

Examples of how transition metals are used as catalysts in industrial processes:

Answer 15

1- Haber process to manufacture ammonia. Catalysed by finely divided iron catalyst.
2- Contact process, producing sulphur triode. Catalysed by vanadium oxide (V2O5)
3- catalytic decomposition of hydrogen peroxide uses manganese (V1) oxide as the catalyst.

Question 16

Is a ligand like a nucleophile or electrophile?

Answer 16

Nucleophile

ligands have a negative charge or a lone pair of electrons capable of being donated

Question 17

What is the Co-ordination number?

Answer 17

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

Question 18

What are Monodentate ligands? give some examples

Answer 18

can form only one dative bond to the central metal ion.

eg. H20, NH3, CL-,CN-

Question 19

What are Bidentate ligands? Give some examples

Answer 19

can each form two dative bonds to the central metal ion, as each ligand contains 2 atoms with a lone pair.

eg. 1,2-diaminoethane (H2NCH2CH2NH2) which is also written as ‘en’ or Ethanedioate ion (C2O42- ) which is sometimes written as ‘ox’

Question 20

How many coordinate bonds are present in an octahedral complex?

Answer 20

six coordinate bonds
could be 6 monodentate bonds or 3 bidentate ligands.

Question 21

How many coordinate bonds are present in a tetrahedral shape?

Answer 21

4 coordinate bonds.

Question 22

How many coordinate bonds are present in a square planar?

Answer 22

4 coordinate bonds.

this is used instead of the tetrahedral most commonly when platinum is the central ion. (When the transition metal have 8 d-electrons in the highest energy d sub shell)

Question 23

How many coordinate bonds are present in a square planar?

Answer 23

4 coordinate bonds.

this is used instead of the tetrahedral most commonly when platinum is the central ion. (When the transition metal have 8 d-electrons in the highest energy d sub shell)

Question 24

What is cis isomerism?

Answer 24

Same side

Question 25

What is trans isomerism?

Answer 25

opposite sides

Question 26

What is optical isomerism?

Answer 26

the two forms are non-superimposable mirror images of each other. They have no plane of symmetry, and one image cannot be placed directly on top of the other.

They are mirror images of each other.

Question 27

What is cis-platin?

Answer 27

A drug used to treat cancer in chemotherapy.

Question 28

How does cis-platin work?

Answer 28

The cis-platin works by binding to the nitrogen atoms on the bases in DNA

The cis-platin passes through the cell membrane and undergoes ligand exchange where the chlorines are replaced by water molecules

The nitrogen is a better ligand than water and forms dative covalent bonds with the cis-platin

The cis-platin distorts the shape of the DNA and prevents the DNA from replicating

In short- it forms a platinum complex inside a cell which binds to DNA and prevents the DNA from replicating.

Question 29

Weaknesses to using cis-platin to fight cancer..?

Answer 29

Cis-platin binds to healthy cells as well as cancerous cells, but affects cancer cells more as they are replicating faster. Unfortunately, this means that other healthy cells which replicate quickly, such as hair follicles, are also affected by cis-platin.

Question 30

What is ligand substitution?

Answer 30

one ligand in a complex is replaced by another.
It forms a new complex that is more stable.

Question 31

Explain the substitution with copper II complexes in water with NaOH and NH3..

Answer 31

The [Cu(H2O)6]2+ (aq) complex ion is blue in colour.
Upon dropwise addition of sodium hydroxide (NaOH) solution, a light blue precipitate is formed.
Partial ligand substitution of two water ligands by two hydroxide ligands has occurred.
Upon addition of excess concentrated ammonia (NH3) solution, the pale blue precipitate dissolves to form a deep blue solution.

Partial ligand substitution has occurred and [Cu(NH3)4(H2O)2] is formed.

Question 32

What would happen if concentrated ammonia was added dropwise to [Cu(H2O)6] instead of NaOH?

Answer 32

The same light blue precipitate would have formed, and it will dissolve to form a dark blue solution if excess ammonia is added.

Question 33

Explain the substitution with copper II complexes in water with concentrated HCL..

Answer 33

The water ligands in [Cu(H2O)6]2+ can also be substituted by chloride ligands.

This forms [Cu(Cl)4]. There is a change in coordination number as the chloride ligands are larger in size so fewer fit around the central Cu2+ ion.

the blue solution turns yellow. With an intermediate of green due to the yellow and blue mixing

If you add water this will reverse.

Question 34

Explain the substitution with chromium II complexes in water with NaOH and NH3..

Answer 34

When chromium III potassium sulphate (KCr(SO4)2 12H2) is dissolved in water it forms [Cr(H20)6]. This is a pale purple solution.

When chromium III sulphate is dissolved in water its a green solution of [Cr(H2O)5SO4]+. One ligand of H2O has been replace.

When ammonia is added drop-wise to [Cr(H20)6] it first creates a grey-green precipitate of Cr(OH)3.

This precipitate dissolves in excess ammonia to form [Cr(NH3)6]3+ and it becomes purple.

Question 35

How does ligand substitution in haemoglobin work? (oxygen and carbon monoxide)

Answer 35

The haem molecule is a complex with iron(II) at its centre, Oxygen atoms form a dative covalent bond with the Fe(II) which enables oxygen molecules to be transported around the body in the blood.

Oxygen molecules are not very good ligands and bond weakly to the iron(II). The weak bonds allows them to break off easily and be transported into cells. (forms oxyhemoglobin).

Carbon monoxide is toxic because it is a better ligand than oxygen and binds strongly and irreversibly to the iron(II) preventing oxygen from being carried to the cells.